DNVGL-OS-E402 Diving systems - Rules and standards - DNV

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DNV GL AS

OFFSHORE STANDARDS

DNVGL-OS-E402 Edition January 2017

Diving systems

FOREWORD

DNV GL offshore standards contain technical requirements, principles and acceptance criteriarelated to classification of offshore units.

© DNV GL AS January 2017

Any comments may be sent by e-mail to [email protected]

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of thisdocument. The use of this document by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibilityfor loss or damages resulting from any use of this document.

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Offshore standards, DNVGL-OS-E402. Edition January 2017 Diving systems

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CHANGES – CURRENT

This document supersedes DNV-OS-E402 Offshore standard for Diving systems, October 2010 and DNV-DS-E403 Standard for Surface Diving Systems, July 2012Changes in this document are highlighted in red colour. However, if the changes involve a whole chapter,section or sub-section, normally only the title will be in red colour.

January 2017, entering into force 1 July 2017• GeneralThe following main changes were implemented in this document:

— Combination of the content of the superseded documents referred above.— Updating of (design) references to DNV GL service documents incl. DNV GL rules for classification: Ships.— Focusing of the scope of the document on diving systems by removal of content related to diving support

vessels/unit arrangements and outer areas.— Removing procedural descriptions and requirements related to classification.

In addition to the above, the following detail changes were made:

• Ch.2 Sec.2 Life support systems including piping, hoses, valves, fittings, compressors,filters and umbilicals— Ch.2 Sec.2 [5.1.4]: Restrict the use of threaded pipe penetrations to max. thread size M30.— Ch.2 Sec.2 [8]: Restrict the use of detachable connections to max 25 mm (1”).

• Ch.3 Sec.1 Design philosophy and premises— Ch.3 Sec.1 [9.1.2]: Removed reference to specific parts of ISO 9001.

• Ch.3 Sec.2 Pressure vessels for human occupancy, gas storage and other purposes— Ch.3 Sec.2 [1.6.2], Ch.3 Sec.2 [2.3.10] Guidance note, Ch.3 Sec.2 [4.1.3] and Ch.3 Sec.2

[4.1.3]Guidance note, design life with respect to fatigue to be defined by the designer.— Ch.3 Sec.2 [5.1.5]: Added guidance note.

• Ch.3 Sec.3 Life support systems— Ch.3 Sec.3 [5.1.6]: Restrict the use of threaded pipe penetrations to max. thread size M30.

• Ch.3 Sec.6 Launch and recovery systems— Ch.3 Sec.6 [3.2.1]: Text related to safety factors revised to be in line with Ch.2 Sec.6 [3.2.1].

• Ch.3 Sec.7 Pipes, hoses, valves, fittings, compressors, filters and umbilicals— Ch.3 Sec.7 [4.1.1]: Restrict the use of detachable connections to max 25 mm (1”).— Ch.3 Sec.7 [5.1.4]: Updated and more specific requirements to the compressor/filter pack.

Editorial corrections

In addition to the above stated changes, editorial corrections may have been made.

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CONTENTS

Changes – current............................................................3

Chapter 1 Introduction..................................................... 8Section 1 General................................................................................................................ 8

1 Introduction......................................................................................................... 8

2 References........................................................................................................... 9

Chapter 2 Surface diving systems...................................25Section 1 Design philosophy and premises........................................................................25

1 Introduction....................................................................................................... 25

2 Documentation philosophy.................................................................................25

3 Safety philosophy...............................................................................................27

4 Surface diving system philosophy......................................................................29

5 External and internal environmental conditions.................................................31

Section 2 Pressure vessels for human occupancy, gas storage and other purposes...........35

1 Introduction....................................................................................................... 35

2 General principles for design of chambers.........................................................39

3 Welded pressure vessels, materials, fabrication and strength........................... 42

4 Gas cylinders......................................................................................................44

5 Acrylic plastic windows......................................................................................45

Section 3 Life support systems including piping, hoses, valves, fittings, compressors,filters and umbilicals.................................................................................................... 47

1 Introduction....................................................................................................... 47

2 Gas storage........................................................................................................52

3 Gas distribution and control system.................................................................. 53

4 Diver’s heating and environmental conditioning in chambers............................ 55

5 Piping systems...................................................................................................57

6 Hoses................................................................................................................. 57

7 Valves.................................................................................................................58

8 Fittings and pipe connections............................................................................ 59

9 Pressure regulators............................................................................................59

10 Compressors for breathing gas systems.......................................................... 59

11 Purification and filter systems......................................................................... 59

12 Umbilicals.........................................................................................................60

Section 4 Electrical systems.............................................................................................. 61

1 Introduction....................................................................................................... 61

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2 System design....................................................................................................63

3 Equipment in general.........................................................................................66

4 Miscellaneous equipment................................................................................... 67

5 Cables.................................................................................................................68

Section 5 Fire prevention, detection and extinction.......................................................... 69

1 Introduction....................................................................................................... 69

2 Fire protection................................................................................................... 70

3 Fire detection and alarm system....................................................................... 70

4 Fire extinguishing.............................................................................................. 71

5 Miscellaneous equipment................................................................................... 71

Section 6 Launch and recovery systems (LARS)................................................................72

1 Introduction....................................................................................................... 72

2 Design principles................................................................................................74

3 Strength............................................................................................................. 77

Section 7 Instrumentation and communication................................................................. 80

1 Introduction....................................................................................................... 80

2 Instrumentation................................................................................................. 81

3 Communication...................................................................................................85

Section 8 Evacuation systems........................................................................................... 87

1 Introduction....................................................................................................... 87

Chapter 3 Saturation diving systems.............................. 88Section 1 Design philosophy and premises........................................................................88

1 Introduction....................................................................................................... 88

2 Safety philosophy...............................................................................................88

3 General premises............................................................................................... 90

4 System design principles................................................................................... 91

5 Diving system arrangement and layout............................................................. 93

6 Environmental conditions...................................................................................93

7 External and internal system condition..............................................................96

8 Documentation................................................................................................... 97

9 Inspection and testing.......................................................................................99

10 Marking and signboards.................................................................................102

Section 2 Pressure vessels for human occupancy, gas storage and other purposes.........104

1 General.............................................................................................................104

2 General principles for design of chambers and bells........................................107

3 Welded pressure vessels, materials and fabrication........................................ 109

4 Strength of welded pressure vessels............................................................... 111

5 Gas cylinders....................................................................................................112

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6 Acrylic plastic windows....................................................................................114

Section 3 Life support systems........................................................................................116

1 General.............................................................................................................116

2 Gas storage......................................................................................................117

3 Gas distribution................................................................................................119

4 Oxygen systems...............................................................................................121

5 Piping systems.................................................................................................121

6 Environmental conditioning in bell and chambers............................................122

7 Gas control systems.........................................................................................124

8 Closed circuit breathing systems (CCBS)......................................................... 125

9 Diving crew facilities........................................................................................126

Section 4 Electrical, instrumentation and communication systems..................................127

1 General.............................................................................................................127

2 System design..................................................................................................129

3 Equipment selection and installation............................................................... 132

4 Communication.................................................................................................133

5 Instrumentation............................................................................................... 136

Section 5 Fire prevention, detection and extinction........................................................ 139

1 General.............................................................................................................139

2 Fire protection................................................................................................. 140

3 Fire detection and alarm system......................................................................140

4 Fire extinguishing............................................................................................ 140

Section 6 Launch and recovery systems..........................................................................142

1 General.............................................................................................................142

2 Design principles..............................................................................................143

3 Strength........................................................................................................... 145

Section 7 Pipes, hoses, valves, fittings, compressors, filters and umbilicals....................148

1 General.............................................................................................................148

2 Components and hoses for oxygen services.................................................... 149

3 Pipes and hoses............................................................................................... 150

4 Valves and pressure regulators....................................................................... 151

5 Fittings and pipe connections.......................................................................... 151

6 Compressors.....................................................................................................151

7 Purification and filter systems......................................................................... 151

8 Umbilicals.........................................................................................................152

Section 8 Hyperbaric evacuation systems....................................................................... 154

1 Introduction..................................................................................................... 154

Appendix A Selection of safety objective...................... 165

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1 Introduction........................................................................................ 1652 Trigger questions................................................................................ 1653 Systematic review/analysis................................................................ 167

Appendix B Dynamic loads in bell handling systems..... 1681 General................................................................................................1682 Loads on negative buoyant bell.......................................................... 1693 Loads on a positive buoyant bell (at surface)..................................... 1724 Design loads........................................................................................172

Changes – historic........................................................174

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CHAPTER 1 INTRODUCTION

SECTION 1 GENERAL

1 Introduction

1.1 Objectives

1.1.1 The objectives of this standard are to give criteria and guidance on design, fabrication, installation,testing and commissioning of diving systems.

1.1.2 Further objectives of this standard are to:

a) provide an internationally acceptable standard of safety for diving systems by defining minimumrequirements for the design, materials, fabrication, installation, testing, commissioning, operation, repair,and re-qualification

b) serve as a technical reference document for classification and verification servicesc) serve as a technical reference document in contractual matters between purchaser and contractord) serve as a guideline for designers, purchaser, and contractors.

1.1.3 General guidance is provided as to the use and interpretation of the standard and text from IMO codeof safety for diving systems, 1995 resolution A.831 (19) is included for reference. In the IMO text, this codeis referred to as the code.

1.1.4 The text from IMO code of safety for diving systems, 1995 resolution A.831 (19) is included asnormative reference.

1.2 Scope

1.2.1 The scope is defined in each section for the various disciplines and may refer to standards that applyto the discipline in general, such as for electrical systems. In these cases this document only containsrequirements that are particular to diving systems, whereas the generic requirements are given in thereferred rules, standard or code. The combined requirements shall then constitute the scope.

1.2.2 Requirements for the diving support vessels, such as the requirements for floatation and positioningability, are not given in this standard but provided in DNVGL-RU-SHIP Pt.5 Ch.10.

1.2.3 Where the code requires that a particular fitting, material, appliance, apparatus, item or type ofequipment should be fitted or carried in a system, or that any particular provision should be made, or anyprocedure or arrangement complied with, the administration may allow alternative arrangements in thatsystem, provided that the administration is satisfied that such alternatives are at least as effective as therequirements of the code.(See IMO code of safety for diving systems Ch.2 design, construction and survey 1.5 equivalents.)

1.2.4 This standard is not applicable to SCUBA diving, submersibles including atmospheric diving suits orsubmarines.

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1.3 Application

1.3.1 Where reference is made to codes other than DNV GL documents, the valid revision shall be taken asthe revision that was current at the date of issue of this standard.

1.3.2 In case of conflict between requirements of this standard and a reference document, the requirementsof this standard shall prevail.

1.3.3 For use of this standard as basis for classification including the relevant procedural requirements see DNVGL-RU-OU-0375 Rules for classification of diving systems

1.4 Document structure

1.4.1 Besides this introduction chapter, this standard consist of two technical chapters:

— Ch.2 Describing design philosophy and all technical and procedural requirements for surface divingsystems

— Ch.3 Describing design philosophy and all technical and procedural requirements for saturation divingsystems

1.4.2 General applicable procedural requirements, including documentation and survey and testing areincluded in the sub-section [1] of the relevant sections both chapters.

1.4.3 Ch.2 is completed with an appendix providing guidance on the selection of a safety objective.

1.4.4 Ch.3 is completed with an appendix providing guidance on dynamic loads in bell handling systems.

2 References

2.1 Normative referencesThe latest revisions of the following documents apply as normative references:

Table 1 Rules and standards for certification

Reference Title

DNVGL-RU-SHIP Rules for classification: ships

DNVGL-RU-OU Rules for classification: offshore units

DNVGL-ST-0378 Standard for offshore and platform lifting appliances

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Table 2 Offshore standards

Reference Title

DNVGL-OS-A101 Safety principles and arrangements

DNVGL-OS-D201 Electrical installations

DNVGL-OS-D202 Instrumentation, safety and telecommunication systems

DNVGL-OS-D301 Fire protection

Table 3 Class programme

Reference Title

Type approval DNVGL-CP-0183 Flexible hoses, non-metallic materials

Type approval DNVGL-CP-0184 Flexible hoses with permanently fitted couplings, metallic materials

Table 4 Class guidelines

Reference Title

DNVGL-CG-0169 Quality survey plan for offshore class new building surveys

Table 5 Recommended practices

Reference Title

DNVGL-RP-E403 Hyperbaric evacuation systems

Table 6 Other normative references

Reference Title

ASME VIII div.1 or div.2 ASME boiler and pressure vessel code rules for construction of pressurevessels

ASME PVHO-1 Safety standard for pressure vessels for human occupancy

ASME PVHO-2 Safety standard for pressure vessels for human occupancy: in serviceguidelines

ASTM G93-03 Standard practice for cleaning methods and cleanliness levels for materialsand equipment used in oxygen-enriched environments

API 17E Specification for subsea production control umbilicals

BS 4778 Quality vocabulary, part 2 quality concepts and related definitions, 1991,British standards institute, London

EN 13096 Transportable gas cylinders, condition for filling gases into receptacles,single component gases

EN 13099 Transportable gas cylinders, condition for filling gas mixtures intoreceptacles

EN ISO 10524-1 Pressure regulators for use with medical gases

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Reference Title

EN ISO 9809-1 Gas cylinders, refillable seamless steel gas cylinders, design, constructionand testing, part 1: quenced and tempered steel cylinders with tensilestrength less than 1100 MPa

EN ISO 9809-2 Gas cylinders, refillable seamless steel gas cylinders, design, constructionand testing, part 2: quenced and tempered steel cylinders with tensilestrength greater or equal to 1100 MPa

ISO 6406 Gas cylinders, seamless steel gas cylinders, periodic inspection and testing

EN 10204 Metallic products, types of inspection documents

EN ISO 11120 Gas cylinders, refillable seamless steel tubes for compressed gastransport, of water capacity between 150 l and 3000 l, design constructionand testing

EN 16753 Gas cylinders, periodic inspection and testing, in situ (without dismantling)of refillable seamless steel tubes of water capacity between 150 l and3000 l, used for compressed gases

EN 13445 Unfired pressure vessels

EN 12021 Respiratory equipment compressed gases for breathing apparatus

ISO/IEC/17065:2012 Conformity assessment, requirements for bodies certifying products,processes and services

EN 1708-1 Welding, basic weld joint details in steel, part 1 pressurized components

IMO resolution A.831 (19) Code of safety for diving Systems, 1995

IMO resolution A.692 (17) Guidelines and specifications for hyperbaric evacuation systems, 1991

IMO MSC/circ.645 of 6 June 1994 Guidelines for vessels with dynamic positioning systems

IMO Res. MSC 149 (77) See SOLAS reg. III/6.2.1

IMO Res. MSC 307 (88) (FTP code)

IMO Res. MSC337 (91) Code on noise levels on-board ships

IEC No.79-10 International Electro technical Commission's publication No.79-10, andIMO (MODU) code Ch.6

ISO 6385-2004 Ergonomic principles in the design of work systems

ISO 9000 Quality management

ISO 10013 Guidelines for quality management system documentation

ISO 10380, BS 6501 Pipework, corrugated metal hoses and hose assemblies

ISO 10474 Steel and steel products, inspection documents

ISO 13628-5 Petroleum and natural gas industries, design and operation of subseaproduction systems, part 5: subsea control umbilicals

PD 5500:2009 + latest amendments Specification for unfired fusion welded pressure vessels

Note: see also Appendix C list of sources to assist in obtaining reference documents

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2.2 Informative references

Table 7 Informative references

Reference Title

NORSOK Standard U-100 Manned underwater operations

ISO 10297 Gas cylinders, cylinder valves, specification and type testing

ISO 11114-3 Gas cylinders, compatibility of cylinder and valve materials with gascontents, part 3: autogenous ignition test in oxygen atmosphere

ISO 10524-1 Part 1: pressure regulators for use with medical gases, part 1: pressureregulators and pressure regulators with flow-metering devices

ISO 10297 Gas cylinders cylinder valves and type testing

(NFPA) Codes National fire protection agency

SOLAS 1974 , Consolidated edition International convention for the safety of life at sea

Guidance note:

The latest revision of the DNV GL documents may be found in the publication list at the DNV GL website www.dnvgl.com.

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2.3 Terminology and definitions

2.3.1 Verbal forms

Term Definition

shall verbal form used to indicate requirements strictly to be followed in order to conform to the document

should verbal form used to indicate that among several possibilities one is recommended as particularly suitable,without mentioning or excluding others, or that a certain course of action is preferred but not necessarilyrequired

may verbal form used to indicate a course of action permissible within the limits of the document

Note: in the cases where text from the IMO code of safety for diving systems Ch.2. design, construction and surveyis used, the IMO use of should shall be interpreted as shall.

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2.4 Definitions

Term Definition

Administration The government of the state whose flag a ship or floating structure which carries adiving system is entitled to fly or in which the ship or floating structure is registered

(see IMO code of safety for diving systems Ch.2 design, construction and survey1.3.1)

Agreement, by agreement Unless otherwise indicated, accepted/agreed in writing between manufacturer/contractor and purchaser. When the standard is applied as basis for certification orclassification by DNV GL, the terms shall mean approved upfront in writing by DNVGL.

As-built survey Survey of the installed and completed diving system, which is performed to verifythat the completed installation work meets the specified requirements, and todocument deviations from the original design, if any.

Basket A divers basket (sometimes known as a stage) is a frame and mesh constructiondesigned to accommodate divers whilst they are lifted in and out of the water

Bell A diving bell is a frame incorporating a dome, and including appendages, for transferof divers between the underwater work site and the deck or the surface chamber(TUP or DDC). In the context of this standard, bell is defined as an open bell/wet-bell. (See open bell, closed bell and wet bell)

Bottle A pressure container for the storage and transport of gases under pressure


Breathing gases All gases and gas mixtures which are used during diving missions respectivelyduring use of breathing apparatus. Depending on the grade of oxygen,complimentary rules may be taken into consideration. The most common breathinggases used for diving are air, nitrox, HeMix, Trimix and pure oxygen.

Builder Signifies the party contracted to build a diving system in compliance with thisstandard

Built in breathing system (BIBS) A system of gas delivery to masks, located in the decompression chambers, basketsand wet-bells. This system facilitates breathing in the event of a contaminatedatmosphere, and allows for the use of therapeutic gases during decompression.BIBS may in rare cases be closed circuit breathing systems (see CCBS definition)but are normally open circuit systems where the exhaled gas is dumped toatmosphere.

Category A machinery spaces Those spaces and trunks to such spaces as defined in the international conventionfor the safety of life at sea, 1974, as amended

(See IMO code of safety for diving systems Ch.2 design, construction and survey1.3.20)

Chamber Surface decompression, pressure or compression chambers (see also DDC),hereafter called the chambers, and are pressure vessels for human occupancy.

Closed bell A sealed submersible diving chamber (SDC) that locks on and off the chamberwhere the divers decompress (DDC). Pressure differentials are retained by way of aclosed door sealing the divers in at pressures, elevated or lowered compared to thesurrounding pressure.

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Term Definition

Closed circuit breathing system(CCBS)

A system for supply of breathing gas to the diver and saving of his exhaled gases forre-circulation after scrubbing and replenishing

Commissioning In relation to diving systems, refers to activities which take place after installationand prior to operation, comprising the tests and trials

Compact umbilical Umbilical consisting of composite bundles of hoses, cables and strength members ina braiding or sheathing

Compartment Part(s) of a chamber sufficiently large to contain at least one person and which mayhave an internal pressure different from adjacent compartments

Competent body/competentperson

In this context defined as a company, organisation or person recognised as fit tocarry out specified inspections or tests. The recognition may be by DNV GL or by astatutory agency.

Compressor A mechanical device that increases the pressure of a gas by reducing its volume.The increase of pressure may be carried out by pistons, screws or diaphragms. Acompressor designed with inlet (suction) pressure above atmospheric is defined asbooster. Depending on the application medium, purification and/or filter systemsmay be provided downstream.

Construction phase All phases during construction, including fabrication, installation, testing andcommissioning, up until the installation or system is safe and operable for intendeduse. In relation to diving systems, this includes procurements, manufactureassembly, rectification, installation, testing, commissioning and repair.

Contractor A party contractually appointed by the purchaser to fulfil all, or any of, the activitiesassociated with design, construction and operation

Control stations Normally as defined in reg.3 and referred to in regulation 20, Ch.II-2 of theInternational Convention for the Safety of Life at Sea. Control stand or controlstation is a control station in which one or more of the following control andindicator functions are centralized:

a) indication and operation of all vital life support conditions, including pressurecontrol

b) visual observation, communication systems including telephones, audio-recording and microphones to public address systems

c) disconnection of all electrical installations and Insulation monitoring.d) provisions for calibration of and comparison between gas analysinge) indication of temperature and humidity in the inner areaf) alarms for abnormal conditions of environmental control systemsg) fixed fire detection and fire alarm systemsh) ventilation fansi) automatic sprinkler, fire detection and fire alarm systemsj) launch and recovery systems, including interlock safety functionsk) operation and control of the hyperbaric evacuation system.

Corrosion allowance Extra wall thickness added during design to compensate for any reduction in wallthickness by corrosion (internally and externally) during operation

Demobilised Diving system is stored on shore and requires a full maintenance regime formobilisation

Deck decompression chamber(DDC)

Deck mounted pressure vessel for human occupancy used for decompression

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Term Definition

Depth The water depth or equivalent pressure to which the diver is exposed at any timeduring a dive or inside a surface compression chamber or a diving bell


Design All related engineering to design of the diving system

Design life The initially planned time period from initial installation or use until permanentdecommissioning of the equipment or system. The original design life may beextended after a re-qualification.

Design load For PVHOs see Ch.2 Sec.3, Ch.3 Sec.2. For LARS see Ch.2 Sec.6 and Ch.3 Sec.6.

Design phase An initial phase that takes a systematic approach to the production of specifications,drawings and other documents to ensure that the diving system meets specifiedrequirements (including design reviews to ensure that design output is verifiedagainst design input requirements). See ISO 9001.

Design temperature, minimum The lowest possible temperature to which the equipment or system may be exposedto during installation and operation, irrespective of the pressure. Environmental aswell as operational temperatures shall be considered.

Guidance note:

For LARS the design temperature is defined in DNVGL-ST-0378 standard for offshoreand platform lifting appliances.


Design temperature, maximum: The highest possible temperature to which the equipment or system may beexposed to during installation and operation. Environmental as well as operationaltemperatures shall be considered.

Diver heating A system for actively heating the divers in the water or in the inner area

Divers Personnel subjected to higher ambient pressure than one atmosphere

Diving bell A submersible compression chamber, including its fitted equipment, for transferof diving personnel under pressure between the work location and the surfacecompression chamber


Diving system The whole plant and equipment necessary for the conduct of diving operations


Diving system (in DNV GL terms) The whole plant and equipment necessary for safe conduct of diving operationswhere compression and decompression of divers are taking place

dmax Maximum operating depth of the surface diving system. This is the depthcorresponding to the maximum pressure for pressurizing divers. (For Classifiedsystems this may be specified in the certificate and data sheet).

ECU Environmental control unit. Maintains Temperature, reduces humidity and mayinclude removal of carbon dioxide.

Enriched Air Nitrogen oxygen mixtures with elevated oxygen content (see NITROX)

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Term Definition

Equipment lock A pressure tight independent lock mounted on the shell of the chamber providingthe means for locking in equipment necessary for the divers and the operation of thesystem (see also medical lock)

Evacuation system A system whereby divers under pressure can be safely evacuated from a ship orfloating structure to a position where decompression can be carried out


Fabrication Activities related to the assembly of objects with a defined purpose. In relation todiving systems, fabrication refers to e.g. deck decompression chambers, wet-bells,and pressure vessels for gas storage, environmental control systems, launch andrecovery systems etc.

Fabricator The party performing the fabrication (in this context, normally of windows forPVHOs)

Failure An event affecting a component or system and causing one or both of the followingeffects:

— loss of component or system function— deterioration of functional capability to such an extent that the safety of the

installation, personnel or environment is significantly reduced.

Fatigue Cyclic loading causing degradation of the material

Flag administration The maritime administration of a vessel's country of registry

Gas See breathing gas

Gas containers Cylinders, bottles and pressure vessels for storage of pressurized gas

Guidance notes Contain advice which is not mandatory for the assignment or retention of class, butwith which the Society, in light of general experience, advises compliance

Handling system The plant and equipment necessary for raising, lowering and transporting the divingbell between the work location and the surface compression chamber

(see IMO code of safety for diving systems Ch.2 design, construction and survey1.3.10) (see launch and recovery system (LARS))

Hazard A deviation (departure from the design and operating intention) which could causedamage, injury or other form of loss (chemical industries association HAZOP guide).

Hazardous areas Those locations in which an explosive gas-air mixture is continuously present, orpresent for long periods (zone O); in which an explosive gas-air mixture is likelyto occur in normal operation (zone 1); in which an explosive gas-air mixture it notlikely to occur, and if it does it will only exist for a short time (zone 2).


HAZOP (hazard and operabilitystudy)

The application of a formal systematic critical examination to the process andengineering intentions of new or existing facilities to assess the hazard potentialof inadvertent operation or malfunction of individual items of equipment and theirconsequential effects on the facility as a whole (chemical industries associationHAZOP guide)

Hydro-test or hydrostatic test See pressure test

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Term Definition

Hyperbaric evacuation system(HES)

System for evacuating divers under pressure. This includes the hyperbaricevacuation unit (HEU), the launch and recovery and control systems.

Hyperbaric rescue vessel (HRV) IMO uses the term hyperbaric evacuation unit (HEU) see above

Inner area The areas which are inside the chambers. Interconnecting trunks are consideredpart of the inner area when the door is opened into the chamber.

Inspection Activities such as measuring, examination, testing, gauging one or morecharacteristics of a product or service and comparing the results with specifiedrequirements for determine conformity

Installation (activity) The operations related to installing the equipment, diving system or supportstructure, e.g. mounting chambers and handling systems etc., including final testingand preparation for operation

Installation manual (IM) A document prepared by the contractor to describe and demonstrate that theinstallation method and equipment used by the contractor will meet the specifiedrequirements and that the results can be verified

Launch and recovery system(LARS)

The system and equipment necessary to launch and recover the divers, the diver’sbasket or wet-bell to the chambers as well as transport the divers between thesurface support unit and the underwater working site, including any guide ropesystems and cursor systems

Lay-up A terminology used for diving systems that are out of commission. In this state thediving system may be installed on board or permanently stored on shore.

Life support system The gas supply, breathing gas system, decompression equipment, environmentalcontrol system and equipment required to provide a safe environment for the divingcrew in the diving bell and the surface compression chamber under all ranges ofpressure and conditions they may be exposed to during diving operations


Life support systems (in DNV GLterms)

The systems comprising gas supply systems, breathing gas systems, pressureregulating systems, environmental control systems, and systems required toprovide a safe habitat for the divers, in the basket, the wet-bell and the chambercompartments under normal conditions during diving operation

Living compartment The part of the surface compression chamber which is intended to be used as themain habitation for the divers during diving operations and which is equipped forsuch purpose


Living compartment (in DNV GLterms)

A compartment which is intended to be used as the main habitation for the diversand which is equipped as such

Load Any action causing stress, strain, deformation, displacement, motion, etc. to theequipment or system

Load effect Effect of a single load or combination of loads on the equipment or system, such asstress, strain, deformation, displacement, motion, etc.

Load effect factor The partial safety factor by which the characteristic load effect is multiplied to obtainthe design load effect

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Term Definition

Lot A number of components from the same batch. E.g. same heat, the same heattreatment batch and with the same dimensions.

Main components Main components of a diving system include the surface compression chamber,diving bell, handling system and fixed gas storage facilities


Manufacture Making of articles or materials, sometimes in larger volumes. In relation to divingsystems, refers to activities for the production of pressure vessels, distributionpanels and other components, performed under contracts from one or morecontractors.

Manufacturer Signifies the entity that manufactures the material or product, or carries out partproduction that determines the quality of the material or product, or does the finalassembly of the product

Mating device The equipment necessary for the connection and a disconnection of a diving bell to asurface compression chamber


Maximum operating depth Maximum operating depth of the diving system is the depth in metres or feetof seawater equivalent to the maximum pressure for which the diving system isdesigned to operate


Medical lock A pressure tight independent lock mounted on the shell of the chamber providingthe means for locking in provisions, medicine and equipment necessary for thedivers and the operation of the system (see also equipment lock)

NDT level The extent and acceptance criteria for the NDT of the components

NITROX Nitrogen oxygen mixtures with elevated oxygen content (see enriched air)

Nominal outside diameter The specified outside diameter. This shall mean the actual outside diameter.

Nominal wall thickness The specified non-corroded wall thickness, which is equal to the minimum steel wallthickness plus the manufacturing tolerance

Normal cubic meters (Nm3) is taken as cubic meters of gas at standard conditions of 0°C and 1.013 bar.

Open bell (also known as wet bell) A suspended canopy chamber, open at the bottom like a moon pool structure thatis lowered underwater to operate as a stage for the divers with the advantage ofproviding an air pocket for refuge and a space for communication outside the mask/helmet

Operation, incidental Conditions that are not part of normal operation of the equipment or system. Inrelation to diving systems, incidental conditions may lead to incidental pressures.

Operation, normal Conditions that arise from the intended use and application of equipment or system,including associated condition and integrity monitoring, maintenance, repairs etc.In relation to diving systems, this should include, start and finish of dives (pre- andpost-dive checks), treatment of decompression-related incidents, gas transfer andchanging out of consumables.

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Term Definition

Operations (phase) The phase when the diving system is being used for the purpose for which it wasdesigned

Pressure, system test In relation to diving systems, this is the internal pressure applied to the componentor system during testing on completion of installation work to test the diving systemfor tightness (normally performed as hydrostatic testing)

Organization Organization means the International Maritime Organization (IMO)


Out of roundness The deviation of the perimeter from a circle. This can be stated as ovalisation (%),or as local out of roundness, e.g. flattening, (mm).

Outer area Those areas of the diving system that are exposed to atmospheric conditions duringoperation, i.e. outside the inner system and the room or area that surrounds orcontains the diving system.

Ovalisation The deviation of the perimeter from a circle. This has the form of an elliptic crosssection.

Owner Signifies the registered owner or manager of the diving system or any otherorganization or person who has assumed the responsibility for operation of thediving system and who on assuming such responsibility has agreed to take over allthe duties and responsibilities. See DNVGL-RU-OU-0101 Ch.1 Sec. 5 [1.2].

Oxygen systems Systems intended for a gas with a higher oxygen percentage than 25

Personal diving equipment Equipment carried by the diver on his person including his tools, diving suit, divinghelmet and self-contained breathing apparatus with gas bottles. This is normally notincluded in the diving system specified in the standard

Plan approval Signifies a systematic and independent examination of drawings, design documentsor records in order to verify compliance with the rules or statutory requirements.Plan approval will be carried out at the discretion of the Society, which also decidesthe extent and method of examination.

Planned maintenance system(PMS)

A system for planning and recording of maintenance activities

Pressure, collapse Characteristic resistance against external over-pressure

Pressure control system In relation to diving systems, this is the system for control of the pressure in thevarious systems, comprising the pressure regulating system, pressure safety systemand associated instrument and alarm systems

Pressure, design In relation to diving system assemblies, this is the maximum internal pressureduring normal operation, referred to a specified reference point, to which thecomponent or system section shall be designed. The design pressure shall takeaccount of the various pressurised components in the adjoining systems, and theirrelative design pressures.

Pressure regulating system In relation to diving systems, this is the system which ensures that, irrespectiveof the upstream pressure, a set pressure is maintained downstream (at a givenreference point) for the component

Pressure safety system The system which, independent of the pressure regulating system, ensures that theallowable set pressure is not exceeded

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Term Definition

Pressure test The hydrostatic pressure test initially performed at the manufacturer of the pressurevessel in accordance with requirements in the design code

Pressure vessel A container capable of withstanding an internal maximum working pressure greaterthan or equal to 1 bar


Purchaser The owner or another party acting on his behalf, who is responsible for procuringmaterials, components or services intended for the design, construction, installationor modification of a diving system

Purification and filter systems Purification and filter systems are used to remove contaminants from breathinggases after compression has taken place

Quality assurance (QA) Planned and systematic actions necessary to provide adequate confidence that aproduct or service will satisfy given requirements for quality

Quality plan (QP) The document setting out the specific quality practices, resources and sequence ofactivities relevant to a particular product, project or contract. A quality plan usuallymakes reference to the part of the quality manual applicable to the specific case.

Quality system Signifies both the quality management system and established production andcontrol procedures

Reliability The probability that a component or system will perform its required functionwithout failure, under stated conditions of operation and maintenance and during aspecified time interval

Re-qualification The re-assessment of a design due to modified design premises and or sustaineddamage

Resistance The capability of a structure, or part of a structure, to resist load effects

Risk The qualitative or quantitative likelihood of an accident or unplanned eventoccurring, considered in conjunction with the potential consequences of such afailure. In quantitative terms, risk is the quantified probability of a defined failuremode times its quantified consequence.

Risk reduction measures Those measures taken to reduce the risks to the operation of the diving system andto the health and safety of personnel associated with it or in its vicinity by:

a) reduction in the probability of failureb) mitigation of the consequences of failure.

Guidance note:

The usual order of preference of risk reduction measures is:

a) inherent safety

b) prevention

c) detection

d) control

e) mitigation

f) emergency response.


Safety objectives The safety goals for the construction, operation and decommissioning of the divingsystem including acceptance criteria for the level of risk acceptable to the owner

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Term Definition

Saturation diving Once a diver becomes saturated with the gases that make decompression necessary,the diver does not need additional decompression. When the blood and tissueshave absorbed all the gas they can hold at that depth, the time required fordecompression becomes constant. As long as the depth is not increased, additionaltime on the bottom is free of any additional decompression.

Self-propelled hyperbaric lifeboat(SPHL)

See HEU [2.3.55]

Significant wave height When selecting the third of the number of waves with the highest wave height, thesignificant wave height is calculated as the mean of the selection

Specified minimum tensilestrength

The minimum tensile strength prescribed by the specification or standard underwhich the material is purchased

Specified minimum yield stress The minimum yield stress prescribed by the specification or standard under whichthe material is purchased

Statement of compliance A statement or report signed by a qualified party affirming that, at the time ofassessment, the defined phase, or collection of activities, met the requirementsstated by the customer

Submersible decompressionchamber (SDC)

Closed bell

Suitable breathing gas A gas or gas mixture that is breathable to divers for the pressure and duration theyare exposed to it

Supplementary requirements Requirements for material properties of component that are additional to the basicrequirements, and that are intended to apply to components used for specificapplications

Surface compression chamber A pressure vessel for human occupancy with means of controlling the pressureinside the chamber


Survey planning document As described in Ch.3 Sec.1 [3.1] document describing the diving system and therequirements to survey and testing throughout the lifetime of the diving system

Top Maximum operation time, i.e. the time from start of pressurization of the diver, untilthe diver is back to atmospheric conditions

Transfer compartment Compartment that is intended to be used for a lock-in or -out operation of diversbetween other compartments or outer area. Also known as TUP (transfer underpressure).

The diving system should be capable of allowing the safe transfer of a person underpressure from the diving bell to the surface compression chamber (and vice versa).


Transferable diving system A diving system designed to be easily transferable in one or more units and whichmay be installed on-board a ship, barge or offshore platform for a short periodof time not exceeding one year. A transferable diving system may be assembledfrom different units into a particular configuration suitable for a specific workingoperation.

Ultimate tensile strength The measured ultimate tensile strength

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Term Definition

Umbilical The link between the diving support unit and the diving bell and may containsurveillance, communication and power supply cables, breathing gas and hot waterhoses. The hoisting and lowering strength member may be part of the umbilical.


Umbilical (in DNVGL terms) A link between support vessel and the divers, or the diving wet-bell, which maycontain gas hoses, hot water hose, power supply cables and communication cables

Verification A service that signifies a confirmation through the provision of objective evidence(analysis, observation, measurement, test, records or other evidence) that specifiedrequirements have been met

Wet bell See open bell

Work All activities to be performed within relevant contract(s) issued by owner, builder ormanufacturer

Working weight Of the basket or wet-bell shall be taken as the maximum weight of the fullyequipped basket or wet-bell, including each fully equipped diver (150 kg for SAT and200 kg for Surface). The load from this weight applies to:

a) launch and recovery in airb) launch and recovery submerged, combining the maximum negative buoyancy

of the wire rope, umbilical and basket or wet-bell at maximum operating depth.

Yield Stress The measured yield tensile stress

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2.5 Abbreviations and symbols

Abbreviation Definition

AE Acoustic emission testing

API American Petroleum Institute

ASME American Society of Mechanical Engineers

ASTM American Society for Testing and Materials

AUT Automatic ultrasonic testing

BS* British Standard

C-Mn Carbon manganese

CE Conformité Européene (European Conformity)

CRA Corrosion resistant alloy

DP Dynamic positioning

DSV Diving support vessel

EBW Electronic beam welded

ET Eddy current testing

FMEA Failure mode effect analysis

HAZ Heat affected zone

HAZOP Hazard and operability study

HFW High frequency welding

HPIC Hydrogen pressure induced cracking

IACS International Association of Class Societies

IM Installation manual

IMO International Maritime Organisation

ISO International Organisation for Standardisation

KV Charpy value

LBW Laser beam welded

MPQT Manufacturing procedure qualification test

MPS Manufacturing procedure specification

MSA Manufacturing survey arrangement

NACE National Association of Corrosion Engineers

NDT Non-destructive testing alternatively NDE is used with the same meaning

NPD Norwegian Petroleum Directorate

P production

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Abbreviation Definition

Q Qualification

QA Quality assurance

QC Quality control

QP Quality plan

QRA Quantitative risk analysis

ROV Remotely operated vehicle

UTS Ultimate tensile strength

WPS Welding procedure specification

YS Yield stress

*Note: now PD: public document

2.6 Symbols

A = cross section areaD = nominal outside diameterDmax = greatest measured inside or outside diameterDmin = smallest measured inside or outside diameterDi = D-2tnom = nominal internal diameterE = young’s modulusf0 = ovality,

H = wave heightHs = significant wave heightID = nominal inside diameterO = out of roundness, Dmax - Dmin

OD = nominal outside diameterT = operating temperatureTmax = maximum design temperatureTmin = minimum design temperatureTnom = nominal thickness

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CHAPTER 2 SURFACE DIVING SYSTEMS

SECTION 1 DESIGN PHILOSOPHY AND PREMISES

1 Introduction

1.1 Objectives

1.1.1 The objectives of this section are to present the safety philosophy applied in this chapter, to identifyand provide a basis for definition of relevant system design characteristics. These are, key issues required fordesign, construction, operation and re-qualification of surface diving systems.

1.1.2 This section also refers to minimum requirements for documentation for design, manufacture,installation and some operational aspects.

1.2 ScopeThe scope of this section is to outline the requirements for planning and documenting system philosophy,safety philosophy and quality management.

1.3 Marking and signboardsLabels (name plates) of flame retardant material bearing clear and indelible markings shall be placed so thatall equipment necessary for operation (valves, detachable connections, switches, warning lights etc.) can beeasily identified. The labels shall be permanently fixed.

2 Documentation philosophy

2.1 General

2.1.1 This sub-section specifies the general requirements for documentation during diving system design,manufacturing, fabrication, installation, commissioning and operation.

2.1.2 In accordance with quality system requirements, design output shall be documented and expressed interms that can be verified and validated against design input requirements.The supplier shall establish and maintain documented procedures to control all documents and data.

2.1.3 All documentation requirements shall be reflected in a document register. The documentation shallcover design, manufacturing, fabrication, installation and commissioning. As a minimum, the register shallreflect activities from the start of design to operation of the diving system.

2.1.4 The documentation shall be submitted to the relevant parties for acceptance, verification orinformation as agreed in ample time before start of fabrication. Documentation pertaining to the systemphilosophy, concept and manufacturing procedure specification, shall be submitted for approval andinformation at the start of the project to enable systematic review.

2.1.5 Verified documentation shall be available at the work site before manufacturing commences.

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2.2 Documentation of arrangementList and information stating the following particulars for the diving system shall be included in theManufacturing Procedure Specification that shall be submitted at the start of the project:

a) maximum operating depth dmaxb) maximum operation time Topc) maximum number of divers in the basket(s) or wet-bell(s)d) maximum number of divers in the chamber(s)e) maximum operational sea-statef) extract from the operation manual, stating the operational procedures, as basis for the design. Plans

showing general arrangement of the diving system, location and supporting arrangementg) plans showing the lay-out of control stand(s)h) proposed program for tests and trials of systems for normal operation and for emergency use.

2.3 Documentation of installationDetailed plans, drawings and procedures shall be prepared for all installation activities. The following shall asa minimum be covered:

a) diving system location overview (planned or existing)b) other vessel (or fixed location) functions and operationsc) list of diving system installation activitiesd) alignment rectificatione) installation of supporting structuref) installation of interconnecting servicesg) installation of protective devicesh) hook-up to support systemsi) as-built surveyj) final testing and preparation for operation.

2.4 Documentation for systems in operation

2.4.1 Plans for diving system operation, inspection, maintenance and repair shall be prepared in a SurveyPlanning Document prior to start of operation. All operational aspects shall be considered when selecting thediving system concept.

2.4.2 The diving system operational planning shall as a minimum cover:

a) organisation and managementb) start-up and shut-down (pre- and post-dive)c) operational limitationsd) emergency operationse) maintenancef) corrosion control, inspection and monitoringg) general inspectionh) special activities.

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2.4.3 In order to carry out periodical surveys, the minimum documentation shall include:

a) personnel responsible for the operation of diving systemb) history of diving system operation with reference to events which may have significance to design and

safetyc) a log of the total number of dives and hours of operation in the periods between annual surveysd) records of new equipment installed and old equipment removede) the originally approved viewports for the system shall be included in the operational documentationf) installation condition data as necessary for understanding diving system design and configuration, e.g.

previous survey reports, as-built installation drawings and test reportsg) inspection, testing and maintenance schedules and their records.

2.4.4 In case of mechanical damage or other abnormalities that might impair the safety, reliability, strengthand stability of the diving system, the following documentation shall, as a minimum, be prepared prior tostart-up of the diving system:

a) description of the damage to the diving system, its sub-systems or components with due reference tolocation, type, extent of damage and temporary measures, if any

b) plans and full particulars of repairs, modifications and replacements, including contingency measuresc) further documentation with respect to particular repair, modification and replacement, as agreed upon in

line with those for the manufacturing or installation phase.

2.5 Documentation for systems in demobilisationDemobilisation shall be planned and prepared and the evaluation shall include the following aspects:

a) safety aspects, during and after demobilisationb) environmental aspects, e.g. pollutionc) impact on other structuresd) possible reuse of equipment at a later stage (re-qualification and certification).

2.6 Filing of documentation

2.6.1 Maintenance of complete files of all relevant documentation during the life of the diving system is theresponsibility of the owner.

2.6.2 The engineering documentation shall be filed by the owner or by the engineering contractor for thelifetime of the system.

2.6.3 Design basis and key data for the diving system shall be filed for the lifetime of the system. Thisincludes documentation from design to start-up and also documentation from possible major repair ormodification of the diving system.

2.6.4 Files to be kept from the operational and maintenance phases of the diving system shall, as aminimum, include final in-service inspection reports from start-up, periodical and special inspections,condition monitoring records, and final reports of maintenance and repair.

3 Safety philosophy

3.1 GeneralThe integrity of a surface diving system constructed to this standard shall be ensured through a safetyphilosophy integrating the different parts.

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The objective of this standard is that the design, materials, fabrication, installation, commissioning,operation, repair, and re-qualification, of diving systems are safe and conducted with due regard to publicsafety and the protection of the environment.

3.2 Safety objectiveThe purchaser/owner shall define an overall safety objective; planned, established and implemented,covering all phases from conceptual development until demobilisation and scrapping. The safety objectiveshall address the main safety goals as well as establishing acceptance criteria for the level of risk acceptableto the owner.

3.3 Systematic review

3.3.1 All work associated with the design, construction and operation of the diving system shall be suchthat it ensures that the requirements in the safety philosophy are met. As a minimum, it shall ensure thatno single failure shall lead to life-threatening situations for any person or to unacceptable damage to thefacilities or the environment.

3.3.2 A systematic review or analysis shall be carried out at all phases in order to identify and evaluate theconsequences of single failures and series of failures in the diving system, such that necessary remedialmeasures can be taken. The extent of the review or analysis shall reflect the criticality of the diving system,the criticality of a planned operation and previous experience with similar systems or operations. Thisreview shall identify the risk to the operation of the diving system and to the health and safety of personnelassociated with it or in its vicinity.The scope of the review should be agreed upon.

3.3.3 Once the risks have been identified their extent can be reduced to a level as low as reasonablypracticable by means of one or both of:

a) reduction in the probability of failureb) mitigation of the consequences of failure.

The result of the systematic review of these risks is measured against the safety objectives.

3.3.4 Special attention shall be given to the risk of fire and launch and recovery operations.

3.4 Quality management systemsAdequate quality management systems shall be implemented according to requirements in DNVGL-RU-OU-0101 Ch.1 Sec.4 [1.2] to ensure that gross errors in the work for diving system design, construction andoperations are limited.

3.5 Inspection and test plansThe tabular description of the inspections and tests to be carried out during the work is frequently known asthe inspection and test plan (ITP).The following items shall be checked for inclusion within the inspection andtest plan:

a) each inspection and test point and its relative location in the production cycle shall be shownb) the characteristics to be inspected and tested at each point shall be identifiedc) the use of sub-contractors shall be indicated and details of how the verification of sub-contractor’s

quality shall be carried out shall be shownd) hold points established by the constructor, the operator or a third party, where witness or review of the

selected inspection or test is required, shall be shown.

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4 Surface diving system philosophy

4.1 GeneralAs far as reasonable and practicable, a diving system should be designed to minimize human error andconstructed so that the failure of any single component (determined, if necessary, by an appropriate riskassessment) should not lead to a dangerous situation.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.1.)

Guidance note:

Whereas this is a general requirement for the systems, it is recognised that certain components cannot fulfil this requirement inand of themselves. A typical example of this is the pressure vessel for human occupancy with acrylic windows and the umbilicals.

In these cases the applicable standards will specify stringent safety factors. For other cases a formal safety assessment may berequired.


4.2 System integrity

4.2.1 surface diving systems shall be designed, constructed and operated in such a manner that they:

a) fulfil the specified operational requirementsb) fulfil the defined safety objective and have the required support capabilities during planned operational

conditionsc) have sufficient safety margin against accidental loads or unplanned operational conditionsd) consider the possibility of changes in the operating conditions and criteria during the lifetime of the

system.

4.2.2 Any re-qualification deemed necessary due to changes in the design conditions shall take place inaccordance with provisions set out in each section of the standard.

4.3 Essential services

4.3.1 Essential services are herein defined as those services that need to be in continuous operation formaintaining the diving system's functionality with regard to sustaining the safety, health and environment ofthe divers in a hyperbaric environment. This includes services required by the crew monitoring the divers.

4.3.2 Essential services shall be maintained for the period required by safely terminating the surface divingoperation, including time for decompression of the divers.

4.3.3 For services supporting divers in the water, all services are essential. 20 minutes is considered to bethe minimum time required ensuring that the divers are safely recovered to the wet-bell, or to the surface.

4.3.4 For services supporting divers in a wet-bell, all services are essential. 20 minutes is considered to bethe minimum time required ensuring that the divers are safely recovered into the decompression chambersor to the surface.

4.3.5 For services supporting divers in the decompression chambers, all required services are essential. Thespecified maximum decompression schedule is considered to be the minimum time required ensuring that thedivers are safely brought to the surface.

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4.4 Emergency services

4.4.1 Emergency services are herein defined as those services that are essential for safety in an emergencycondition. Examples of equipment and systems for emergency services include:

a) emergency lighting, including external strobe lighting on basket/wet-bellb) emergency communicationc) emergency life support systems involving pressure containment, oxygen supplies and CO2 scrubbingd) emergency heating/cooling systemse) condition monitoring of emergency batteriesf) alarm systems for the above emergency servicesg) emergency launch and recovery of the wet-bell(s)/basket(s)/diver(s) (if electrical).

4.4.2 For services supporting divers in the water, all the above services may be considered emergencyservices and 20 minutes is considered to be the minimum time required to ensure that the divers are safelyrecovered in the wet-bell or basket or to the surface.

4.4.3 For services supporting divers in a wet-bell, all the above services may be considered emergencyservices and 20 minutes is considered to be the minimum time required to ensure that the divers are safelyrecovered in the decompression chambers or to the surface.

4.4.4 For services supporting divers in the decompression chambers, all the above services may beconsidered emergency services with the exception of launch and recovery systems.

4.4.5 Services supporting hyperbaric evacuation system are considered statutory scope and thereforereviewed on a case by case basis according to instructions from the applicable administration.

4.5 Non-important servicesNon-important services are those which are not essential/emergency according to the above.

4.6 Layout and arrangement of the surface diving system

4.6.1 All components in a diving system should be so designed, constructed and arranged as to permit easycleaning, disinfection, inspection and maintenance.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.6.)

4.6.2 The layout of the diving system shall ensure protection from accidental damage and accessibility forsafe operation, maintenance and inspection.The diving system shall be so designed that the divers and assisting personnel are provided with safe andcomfortable operating conditions. Ergonomic principles shall be applied in the design of working systems.(I.e. in accordance with DNVGL-OS-D202 Ch.2 Sec.5 and ISO 6385.)

4.6.3 The elements of the surface diving system shall be configured in such a way as to ensure that aclear access route is available from the LARS to the decompression chamber, with a distance as short aspracticable and not more than that which provides enough time according to the maximum allowable surfaceinterval stipulated in the applied decompression tables.

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4.7 Wet-bell – if installed

4.7.1 If wet-bells are employed, they shall meet the requirements for bells given in this standard.

4.7.2 A diving bell should provide a suitable environment and facilities for the persons who use it, havingregard to the type and duration of the diving operation.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.3.)

4.7.3 Diving bells should be so designed as to provide adequate space for the number of occupantsenvisaged, together with the equipment.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.5.)

5 External and internal environmental conditions

5.1 General

5.1.1 Diving systems and components thereof should be designed for the conditions under which they arecertificated to operate.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.2.)

5.1.2 Systems and components shall be designed for the environmental conditions given in the divingsystem specifications.Bells and baskets shall meet the environmental requirements for surface and submerged components.The specifications shall state the limitations on roll, maximum current etc. in order to avoid the basket/bellimpacting the ships side or getting trapped under bilge keel.

5.1.3 Environmental phenomena that might impair proper functioning of the system or cause a reductionof the reliability and safety of the system shall be considered in the MPS (including fixed and land-basedinstallations) as follows:

a) wind and tideb) waves and currentsc) air and sea temperatures and ice.

5.2 External operational conditions

5.2.1 Materials for diving system components should be suitable for their intended use.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.3.)

5.2.2 Design inclinations shall be assumed according to Table 1 unless otherwise specified in the systemspecifications.

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Table 1 Design inclinations

Location Roll Permanent list Pitch Trim

Chambers and other surface installations:

on a ship+/-22.5° +/-15° +/-10° +/-5°

On a mobile offshore unit +/-15° +/-15°

Components in a basket or wet-bell +/-45° +/-22.5°

Guidance note:

For launch and recovery systems the operational design sea-state is given in Sec.7.


5.2.3 Range of ambient temperature: -10°C to 55°C, unless otherwise specified. For greater temperatureranges, temperature protection shall be provided.

5.2.4 Humidity: 100%.

5.2.5 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at all relevant temperaturesand humidity conditions.

5.3 Internal operational conditions (inner area)

5.3.1 Range of ambient pressure is given by the design code or as a minimum range of 1 bar to 1.3 timesthe pressure corresponding to dmax with pressurisation and depressurisation rates as specified in Ch.2 Sec.3[3.1], whichever is the greater range. This shall be applicable to materials and components installed in thepressure vessels for human occupancy.

5.3.2 Range of ambient temperature: 5°C to 55°C, unless otherwise specified.Guidance note:

Ambient pressure and temperature is here understood to be the pressure and temperature of the environment surrounding theequipment or components utilised in the diving system.


5.3.3 Relative humidity: up to 100%.

5.3.4 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at relevant temperatures andhumidity conditions.

5.3.5 There shall be a limitation on maximum oxygen atmosphere content of 23.5% in manned divingchambers to ensure that the effects from fire-extinguishing systems/extinguishers have the intended effect.

5.3.6 A description of the internal conditions during storage, construction, installation, pressure testing andcommissioning shall be prepared. The duration of exposure to seawater or humid air, and the need for usingmeasures to control corrosion shall be considered.When choosing materials, paints etc. the potential for emission of hazardous compounds shall be considered.

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5.3.7 Statutory requirements apply for determination of exposure limits such as:

a) American Conference of Governmental Industrial Hygienists, documentation of the threshold limit valuesand biological exposure.

b) European Commission Directive on occupational exposure limit values.c) Health and safety executive occupational exposure limits.d) NASA. Spacecraft maximum allowable concentrations for airborne contaminants (SMAC), 1999.e) ACGIH. TLVs and BEIs. Ohio: American Conference of Governmental Industrial Hygienists.f) Segadal K, Djurhuus R, Roseth I. Implementation of a standard procedure for routine surveillance of

chemical contamination of diving atmosphere during diving operations in 1995. Bergen: NorwegianUnderwater Technology Centre AS, 1995; NUTEC report no. 27-95.

g) Djurhuus R, Jakobsen K, Sundland H, Lindrup AG, Solheim E. Procedure for testing for off gassing frommaterials used in diving systems. (In Norwegian). Bergen: Norwegian Underwater Technology Centre AS,1994; NUTEC report no. 5-94.

h) Ahlen C. Cleaning and disinfection of operational saturation diving systems. Recommendations for anindustrial standard. (In Norwegian). Trondheim: SINTEF, 1999; STF78 A99123.

i) Ahlen C, Zahlsen K. FUDT-Bacteriology 1991. Disinfecting in hyperbaric environments. (In Norwegian).Trondheim: SINTEF, 1992; STF23 F92015.

Note that the exposure limits need to be translated into a form relative to the depth exposure andatmosphere.

5.3.8 In order to assess the need for internal corrosion control, including corrosion allowance and provisionfor inspection and monitoring, the following conditions shall be considered:

a) maximum and average operating temperature and pressure profiles of the components, and expectedvariations during the design life

b) expected content of dissolved salts in fluids, residual oxygen and active chlorine in sea waterc) chemical additions and provisions for periodic cleaningd) provision for inspection of corrosion damage and expected capabilities of inspection tools (i.e. detection

limits and sizing capabilities for relevant forms of corrosion damage)e) the possibility of wear and tear, galvanic effects and effects in still water pools shall be considered.

5.4 Submerged components

5.4.1 Range of ambient temperature: -2°C to 30°C.Guidance note:

Ambient temperature may in this case fall outside the range stipulated. This shall be agreed on a case-by-case basis and stated inthe certificates.


5.4.2 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to maximum operatingdepth. Environmental requirements apply to submerged materials and components.

5.4.3 Salinity of ambient water: 35 parts per thousand.

5.4.4 The pressure equivalent to depth of seawater at 0°C with 3.5% salinity may be taken as 1.006 bar per10 msw (meter seawater), as a mean value.For saltwater, the density may be taken to vary as follows:

— 0.05% increase for each 100 m of depth increase— 0.4% increase for an increase in salinity from 3.5% to 4.0%

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— 0.3% decrease for an increase in temperature from 10°C to 20°C.

5.4.5 For the selection and detailed design for external corrosion control, the conditions relating to theenvironment shall be defined.

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SECTION 2 PRESSURE VESSELS FOR HUMAN OCCUPANCY, GASSTORAGE AND OTHER PURPOSES

1 Introduction

1.1 ObjectivesPressure vessels are designed and manufactured to internationally recognised codes and standards. Theobjectives of this section are to give additional requirements that relate to the function of these pressurevessels in a diving system.

1.2 Scope

1.2.1 The following scope of work is included in the requirements of this section:

a) conceptual and detailed design of pressure vessels for human occupancy, for gas storage and for otherpurposes

b) manufacturing of such pressure vesselsc) quality control during manufacturing and fabrication of such pressure vessels including documentation

requirementsd) load conditionse) interlock arrangements for doors and hatches.

1.2.2 ASME PVHO-1 safety standard for pressure vessels for human occupancy shall be used for design ofacrylic plastic windows, regardless of which standard is used for the design of the pressure vessel.

1.2.3 Welding of pressure vessels and general workmanship requirements are given in the relevant rules,codes and standards.

1.3 Application

1.3.1 This section applies to all pressure vessels in surface diving systems designed to comply withthis standard. Note that in addition to this standard, and the applied design standards, further nationalrequirements may apply.

1.3.2 Closed bells are not required for surface diving systems and consequently not included in theapplication of this standard. If closed bells are employed, the complete diving system shall comply with therelevant requirements given in Ch.3.

1.3.3 This section has impact upon [Sec. 8], insofar as it provides the basis for design of the pressurevessels in the hyperbaric evacuation system.

1.4 References

1.4.1 For quantitative design parameters and functional requirements, see relevant standards andguidelines, including normative references given in Ch.1 Sec.2 and DNVGL-RU-SHIP.

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1.4.2 All pressure vessels for human occupancy shall be designed, constructed and tested according to oneof the following codes and standards:

a) EN 13445 unfired pressure vessels.b) ASME PVHO-1, see ASME VIII div.1 or div.2 boiler and pressure vessel code.

1.4.3 Pressure vessels for human occupancy shall be classified in the highest category in the applied code orstandard.

1.4.4 All windows in pressure vessels for human occupancy shall be certified in accordance with ASME-PVHO-1.

1.4.5 Gas cylinders shall be designed, constructed and tested according to one of the following standards,norms or directives:

a) EN ISO 9809-1 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing,part 1: quenched and tempered steel cylinders with tensile strength less than 1100 MPa.

b) EN ISO 9809-2 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing,part 1: quenched and tempered steel cylinders with tensile strength greater or equal to 1100 MPa.

c) EN ISO 11120 gas cylinders, refillable seamless steel tubes for compressed gas transport, of watercapacity between 150 l and 3000 l, design construction and testing.

1.5 DocumentationPressure vessels shall be documented as follows:Plans showing structural arrangement, dimensions, welding seams, attachments and foundations of thechamber and other pressure vessels, with details of doors, locks (medical locks and equipment locks), viewports, penetrations, flanged and welded connections.Plans showing expansion allowances under working conditions for interconnected multi-vessel systems, ifapplicable.Documents stating:

a) grade of materialb) welding methods, type and size of filler metalc) design pressured) particulars of heat treatmente) fabrication tolerancesf) extent and type of non-destructive testing of welded connectionsg) type of thermal insulation materials and particulars, i.e.: flammability and specific heat conductivityh) Drawings and specifications of all windows with detailed drawings and specifications of the penetration

the appropriate window fitting. It shall be determined that the tolerances are sufficient including gaskets,O-rings and retainer rings

i) calculations of thicknesses and or stressesj) fatigue evaluation and if necessary fatigue analysis.

For seamless steel gas cylinders and vessels:

a) plans showing proposed dimensions and details such as valves and safety devices shall be made for eachtype and size of vessel.

Details shall include:

a) production methodb) heat treatment.

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Material specifications for the completed vessel with information on the following:

a) chemical compositionb) tensile strengthc) yield strengthd) elongatione) impact test valuesf) brinell hardness.

The following particulars shall be provided for information:

a) type of gasb) filling pressure at 15°Cc) safety relief valve settingd) weight of empty vessel and volumetric capacitye) material protection.

1.6 Survey and testing requirements during and after manufacture

1.6.1 For welded pressure vessels the following tests have to be carried out in addition to the tests specifiedin the applied design code or standard:

a) all butt welds in diving chambers shall be radiographed over their full lengthb) branches and reinforcement of openings, including all weld connections to the shell, shall be subjected to

100% magnetic particle testing.

1.6.2 When the applied code or standard for welded pressure vessels requires heat treatment of dished endsafter hot or cold forming, mechanical testing may be required after the final heat treatment.

1.6.3 The details between intermediate heads and cylindrical shells of chambers may be done in accordancewith requirements given in:

a) EN 1708-1 welding, basic weld joint details in steel Table 9: internal diaphragms and separatorsb) ASME Sec.VIII div.I Fig.UW-13.1.

1.6.4 Welded pressure vessels and seamless steel gas containers for internal pressure shall be hydrostatictested to an internal pressure in accordance with the design code. Each compartment in chambers shallbe tested separately. In addition pressure test shall be performed with test pressure in each chambersimultaneously.

1.6.5 Pressure vessels for external pressure shall, in addition to the internal pressure testing, be hydrostatictested to an external pressure in accordance with the design code.

1.6.6 Acrylic plastic windows shall be tested in accordance with ASME PVHO-1 Sec.2 [2.7].

1.6.7 For seamless gas cylinders production tests shall be carried out in accordance with the requirementsgiven in the applied code or standard. Further production tests, and required attendance during testing, maybe given in the specifications.

1.6.8 Gas cylinders shall be cleaned and sealed according to accepted industry standards.

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1.7 Survey and testing requirements during and after assemblyThe gas storage and chambers shall be tested for leakage at low pressures and the maximum workingpressure.

1.8 Marking and signboards

1.8.1 All gas containers shall be marked with a consistent colour code visible from the valve end, showingthe name, chemical formula of the gas it contains and the percentage of each gas. Piping systems shall bemarked with a colour code, and there shall be a chart posted in the control room explaining the code.

Table 1 For piping systems and gas storage bottles/pressure vessels the following colour codeshould be used:

Name (Symbol) Colour code

Oxygen (O2) White

Nitrogen (N2) Black

Air (Air) White and black

Carbon dioxide (CO2) Grey

In addition, each bottle/pressure vessel should be marked with the name and symbol given above of the gases itcontains. The marking and colour coding of the gas storage bottles should be visible from the valve end.

(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.9.)

1.8.2 Each gas container shall be permanently and legibly marked on the collar or neck ring (where thethickness of the material is greater than the design minimum) as follows:

a) the design codeb) the manufacturer's mark or namec) the manufacturer's serial numberd) the test pressure (bar) and date of hydrostatic teste) surveyor's mark and identificationf) settled pressure (bar) at 15°Cg) volumetric capacity of the container, in litresh) tare weight, i.e. the mass of the container including valve, in kg.

In addition marking of gas content shall be carried out according to Table 1.

1.8.3 Other pressure vessels shall be permanently and legibly marked at a suitable location in accordancewith the requirements in the design code. As a minimum the following information shall be present:

a) the design codeb) the manufacturer's mark or namec) the manufacturer's serial numberd) the test pressure (bar) and date of hydrostatic teste) the maximum working pressuref) the inspection body’s mark and identificationg) the maximum set pressure of the safety relief valves.

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1.9 Materials

1.9.1 Material specifications and selection associated with the production of pressure vessels are given in theapplied codes and standards (EN/ASME).

1.9.2 Areas of steel pressure vessels that can be subjected to corrosion shall be protected by approvedmeans. The surface of the window seats cavity shall be protected against corrosion.

1.9.3 Windows mounted on chambers shall be protected to avoid damage by impact and to preventchemicals, which can deteriorate the acrylic plastic, to come in contact with the window from the outside.

Guidance note:

Many solvents for paints, acetone and other agents will deteriorate the acrylic plastic and reduce the strength significantly.


1.9.4 All penetrators in pressure vessels for human occupancy shall be designed to minimise corrosion fromany fluid passing through them.

Guidance note:

In some cases this requirement may best be met by the use of a sleeve passing through the hull penetration.


1.9.5 Paints, cabling and other materials shall be considered for toxic or noxious properties.

2 General principles for design of chambers

2.1 General

2.1.1 A diving system should, as a minimum, include either one surface compression chamber with twoseparate compartments, or two interconnected separate chambers so designed as to permit ingress or egressof personnel while one compartment or chamber remains pressurized. All doors should be designed so thatlocking mechanisms, if provided, can be operated from both sides.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.1.)

2.1.2 Where a surface compression chamber is to be used (-omitted, non-applicable text-), it should be soarranged as to allow most divers to stand upright and to stretch out comfortably on their bunks. The smallerof the two compartments should be large enough for at least two persons. One of these compartmentsshould be a living compartment.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.2.)For SURFACE diving systems the minimum inner dimensions measured as free height above the deck platesin the middle of the chamber, shall be 170 cm This may be less if the chamber is only used for stand-bypurposes and if national regulations allow it.

Guidance note:

Statutory requirements may require larger dimensions.


2.1.3 A surface compression chamber should provide a suitable environment and facilities for the personswho use it, having regard to the type and duration of the diving operation. (-Omitted, non-applicable text-).(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.6.)

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2.1.4 All pressure vessels for human occupancy shall be certified.

2.1.5 Wet-bells, if employed, and surface diving baskets shall be of adequate size, be equipped to cater forthe number of divers intended to man them and be equipped for handling unconscious or injured divers.

2.2 Design loads

2.2.1 The design pressure for pressure vessels shall not be less than that corresponding to the maximumoperating pressure as defined in the specifications given in the MPS.

2.2.2 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of fullpressure cycles as defined by the designer. The evvaluation and analysis shall be carried ut according to theapplied design code.

Guidance note:

NDT of the surface of the external weld of the large openings such as windows and locks to detect surface breaking defects shall becarried out at the renewal survey.


2.2.3 The effects of the following loads shall be considered and shall be taken into account, if significant. SeeDNVGL-RU-SHIP Pt.3 Ch.1 Sec.3 Principles and Sec.4:

a) dynamic loads due to movements of the support vesselb) local loadsc) loads due to restrictions in expansionsd) loads due to weight of content during normal operation and pressure testinge) loads due to rough handlingf) the stress evaluation shall apply the distortion theory (von Mises’ criterion).

Guidance note:

Multipurpose vessels may carry relatively heavy deck loads, which can cause stresses and strains on the mountings of the divingsystem components. If this cannot be avoided through design of the installed diving system, it should be monitored during suchoperations.


2.3 Foundations for pressure vessels for human occupancy and for gas storage

2.3.1 The pressure vessels with foundations shall be designed for a static inclination of 30° in any directionwithout exceeding the allowable stresses as specified in the design code.

2.3.2 Suitable foundations and supporting structures shall be provided to withstand a collision force actingon the pressure vessels corresponding to one half the weights of the pressure vessels in the forward directionand one quarter the weight of the pressure vessels in the aft direction.

Guidance note:

The loads mentioned in [2.3.1] and [2.3.2] need not to be combined with each other or with wave-induced loads.


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2.4 Doors, hatches, windows, branches etc.

2.4.1 The living compartment and other compartments intended to be used for decompression should have alock through which provisions, medicine and equipment may be passed into the chamber while its occupantsremain under pressure.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.3.)

2.4.2 Doors and hatches for human transportation shall in general be a minimum diameter of 600 mm.Guidance note:

For doors and hatches in between chambers, standard pipe with nominal bore 24" may be acceptable.


2.4.3 The medical locks shall be large enough to allow lock-in and lock-out of CO2 absorption material andnecessary supplies for the divers.

Guidance note:

National rules and requirements may be more stringent and thereby take precedence (i.e. Norwegian Petroleum Directorate).


2.4.4 Means enabling the doors to be opened from either side shall be provided.Guidance note:

As the above requirement also applies to the internal doors in chambers, it does follow that locking devises are not allowed onthe pressurised side of these doors unless they can be operated from the other side. Clip locks are frequently used on these doorsto prevent slamming due to the vessels movement in the sea. However, the clip setting should be such that they can be pushed/pulled open from either side without the use of excessive force.


2.4.5 Locks should be designed to prevent accidental opening under pressure and, where necessary,interlocks should be provided for this purpose.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.4.)

2.4.6 For:

a) doorsb) hatchesc) mating arrangementsd) pressurised locks and trunkse) pressurised containersf) accompanying equipment under pressure

where opening or unintentional pressure drop may entail danger or cause injury, the closing mechanismsshall be physically secured by locking mechanisms (interlocks).This applies to units which do not seal by pressure and includes, but is not limited to:

a) equipment locksb) medical locksc) soda lime (CO2 scrubber) containers for external regeneration of the chamber environments (if fitted)d) mating arrangements between hyperbaric evacuation units and escape trunks where these are installed.

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2.4.7 The closing mechanisms with accompanying locking mechanisms shall be arranged so that:

a) opening cannot take place unless the pressures are equal on both sides or unless the pressures in theunits are at ambient level

b) correct position of the closing mechanisms and the locking mechanisms shall be ensured before it ispossible to apply pressure

c) the pressures in the units, shall directly control the locking mechanisms, andd) the penetrators and piping for pressure sensing shall be arranged so that blockage is avoided.

Guidance note:

See ASME PVHO-1 with sub reference to ASME VIII D1 UG-35.2(b)(1) and EN 13445-5 C.5.7.3.2.


2.4.8 Trunks between doors shall be equipped with pressure equalising valves. Penetrators for pressureequalising shall be arranged so that blockage is avoided.

2.4.9 Each pressure compartment should have view ports to allow observation of all occupants from theoutside.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.5.)

2.4.10 Windows shall be protected against impact. Impact protection may be provided by:

a) recessing the external surface of the window at least 50 mm below the surrounding structureb) one or more external bumpers extending across the window

2.4.11 Where mountings are secured by studs, these shall have full thread holding in the shell for a length ofat least one diameter. Holes for studs shall not penetrate the shell.

2.4.12 Damage control plugs may be provided to enable the divers to seal off windows to prevent damage orleakage developing.

2.4.13 For pressure vessels where fatigue can be a possible mode of failure, attention shall be given to thepossible adverse effects of the following design features:

a) pad type reinforcement of openingsb) set-on branchesc) partial penetration welds of branches.

2.4.14 For structures that are not covered by the pressure vessel design code, the butt weld and filled weldshall be designed to take shear based on 1.5 times the maximum differential pressure that can exist. Theallowable stress value for the butt weld shall be 70% of the nominal design stress for the shell material andthat of the fillet weld 50%. The area of the butt weld in shear shall be taken as the width at the root of theweld times the length of the weld. The area of the fillet weld shall be taken as the minimum leg dimensiontimes the length of the weld.

3 Welded pressure vessels, materials, fabrication and strength

3.1 Materials

3.1.1 Steel grades shall comply with the applied design code and standard.

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3.1.2 Other material grades may be acceptable after special consideration. In such cases, additional testingmay be required and qualification procedures shall be reconsidered.

3.1.3 Materials for main pressure retaining parts shall be certified.

3.1.4 Stainless steel cladding, stainless steel tubes, fittings etc. which are welded to pressure vessels ofnon-stainless steel shall be of a stabilised or low-carbon grade. Acceptable grades are given in the applicablestandards or in DNVGL-RU-SHIP Pt.2 Ch.2 Sec.4.

3.2 Fabrication

3.2.1 Pressure vessels for diving systems shall be manufactured by works approved by a recognised body,for the production of the type of pressure vessels being delivered.

3.2.2 Welding shall be carried out according to approved drawings.Qualification of welders, welding procedure specifications, welding procedures and testing shall be accordingto the applied design code or standard.

3.2.3 The outside diameter of the head skirt shall have a close fit to the cylinders.

3.2.4 The surface dimensions and finish of seals for hatches and windows are generally to comply with thetolerances specified by the manufacturers of the windows and the sealing systems. The fitting and installationof the window to the flange shall be according to the requirements given in ASME PVHO-1.

3.3 Fabrication tolerances

3.3.1 Fabrication tolerances shall meet the requirements in the applied codes and standards.

3.3.2 Local tolerance requirements for ring frames are given in Ch.3 Sec.2 [3.3.2] for vessels subject toexternal pressure, if applicable.

3.4 Structural analysis to determine strength

3.4.1 In the design of pressure vessels including accessories such as doors, hinges, closing mechanismsand penetrators, the effects of rough handling and accidents should be considered in addition to designparameters such as pressure, temperature, vibration, operating and environmental conditions.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.5.)

3.4.2 Pressure vessels shall be documented by structural analysis for specified design conditions according tothe applied codes and standards.

3.4.3 For details not covered by the applied codes and standards, finite element analysis may be acceptableif properly planned, modelled and documented.Alternatively, by applying strain gauges, stress measurements may be carried out according to an approvedprogramme and shall be properly documented. The tests shall be planned, and carried out during the firstpressure test.

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3.4.4 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of fullpressure cycles and non-pressure loads given in the specification. The evaluation and analysis shall becarried out according to the applied design code and standard. See DNVGL-RU-SHIP Pt.3 Ch.1 Sec.3 andDNVGL-RU-SHIP Pt.3 Ch.1 Sec.4.

3.5 Strength of vessels subjected to external pressureIf applicable Ch.3 Sec.2 [4.2] applies.

4 Gas cylinders

4.1 General

4.1.1 Gas cylinders shall be produced by manufacturers authorised for such production and certified by acompetent inspection body when:

where:p = design pressure in bar.V = volume in m3.The certification level shall as a minimum be manufacturer's works certificates (W). Other levels ofcertification may be required by the terms of delivery.Smaller gas cylinders shall be certified if they provide an essential function in the system.

Guidance note:

Cylinders on-line in a system providing breathing gas to the divers will be considered essential.


4.1.2 The materials applied in the manufacture of gas cylinders shall be certified.

4.1.3 Special attention should be paid to the design and choice of material for the construction of pressurevessels containing oxygen.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.4.1.)

4.1.4 Shell thickness shall meet the criteria given in the applied code or standard for test pressure. Theworking pressure for a given geographical area is given by reference to a standard such as EN 13096transportable gas cylinders, conditins for silling gas into receptacles, single component gases and En 13099transportable gas cylinders, conditions for filling gas mixtures into receptacles.

4.1.5 Corrosion allowance shall be specified in the terms of delivery reflecting the intended use of the gascylinder, but shall not be less than 1 mm.

4.2 Heat treatmentHeat treatment shall follow the requirements given in the applied code or standard, and shall bedocumented.

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4.3 Tolerances and surface conditionsTolerances and surface condition shall meet the criteria given in the applied code or standard, and shall bedocumented in the design documentation. If the applied code or standard does not specify requirementsfor tolerances and surface conditions, then it may be necessary to specify this in the diving systemsspecifications.

5 Acrylic plastic windows

5.1 GeneralThe following requirements apply to windows made from cast stock of unlaminated polymethyl methacrylateplastics, in the following denoted acrylic plastic, with a design life of 10 years, suitable for:

a) 10.000 load cyclesb) sustained temperatures in the range specified by the end user and not less than specified by ASME

PVHO-1c) pressurisation or depressurisation rates not exceeding 10 bar/secondd) use in environments that cannot cause chemical or physical deterioration of the acrylic plastic (i.e.

resistant against saltwater and gases used in life support systems).

5.2 MaterialsMaterials for acrylic plastic windows shall be manufactured and tested in accordance with ASME PVHO-1safety standard for pressure vessels for human occupancy.

5.3 Manufacturers of cast materialManufacturers wishing to supply cast acrylic plastic for diving systems, shall be approved for such production.The material shall have an approved chemical composition and to be produced, heat treated and testedaccording to the ASME PVHO-1 safety standard for pressure vessels for human occupancy. Approval shall begranted on the basis of a thorough test of material from the current production and a report after inspectingthe works, and verification of QA and QC against requirements given in ASME PVHO-1.

5.4 Certification of cast material

5.4.1 Each delivery of cast material shall be accompanied by a certificate issued by the manufacturer(PVHO-1 forms VP-3 and VP-4). The certificate shall (as a minimum) contain the following:

a) name and address of manufacturerb) certificate number and datec) designation of productd) numbers and dimensions of the pieces covered by the certificatee) material test results and propertiesf) signature.

5.4.2 The following text shall be printed in the right uppermost corner of the certificate:This certificate will be accepted by (approval body) on the basis of completed approval tests and the(approval body’s) surveillance of production control and products. The manufacturer guarantees that theproduct meets the requirements of (approval body) and that inspection and tests have been carried out inaccordance with (code or standard).

5.4.3 The cast material shall be marked with the manufacturer's name and with the number and date of thecertificate.

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5.4.4 If a later edition of the ASME standard requires further documentation and markings, the ASMErequirements shall be met.

5.5 Certification of windows

5.5.1 Each batch of acrylic plastic windows used in diving systems shall have a certificate issued by theapproval body, showing the test results and the annealing conditions according to the applicable forms givenin ASME PVHO-1.

5.5.2 Each window shall have an identification marked on it for traceability. Identification of each windowshall include; design pressure, maximum temperature, initials for P.V.H.O., window fabricator's identificationmark, fabricators serial number and year of fabrication.

5.5.3 For ease of viewing, the above information shall be located on the windows seating surface with anindelible marker. Acceptable marking methods are given in ASME PVHO-1.

5.5.4 Stamping or marking that can cause crack propagation is not permitted.

5.6 Geometry and thickness

5.6.1 Windows shall be of the standard designs according to the ASME PVHO-1 safety standard for pressurevessels for human occupancy.

5.6.2 O-ring grooves shall not be located in window bearing surfaces serving primarily as support or in theacrylic window itself.

5.7 Fabrication

5.7.1 The included conical angle of the seating surface of a window shall be within +0.25/-0,00 degrees ofthe nominal value.

5.7.2 The deviation of a spherical window from an ideal sphere shall be less than 0.5% of the specifiednominal external radius of the spherical section.

5.7.3 Each window shall be annealed after all forming and polishing operations are completed. The annealingprocess shall be according to the annealing schedule in ASME PVHO-1.

5.7.4 During the manufacturing process each window shall be equipped with identification and amanufacture process rider for recording of all pertinent data.

5.8 In service inspectionIn service inspection and testing shall be carried out in accordance with requirements given in ASME PVHO-2guidelines.

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SECTION 3 LIFE SUPPORT SYSTEMS INCLUDING PIPING, HOSES,VALVES, FITTINGS, COMPRESSORS, FILTERS AND UMBILICALS

1 Introduction

1.1 ObjectivesThe objectives of this section are to specify requirements for life support systems, including pipes hosesvalves, fittings, compressors and umbilicals, serving surface diving systems. General requirements for pipingsystems are given in DNVGL-RU-SHIP Pt.4 Ch.6.

1.2 Scope

1.2.1 This section is giving guidance on:

a) conceptual and detailed design of life support systemsb) manufacturing of life support systemsc) quality control during manufacturing and fabrication of components and subsystems for life support

systems.

1.2.2 Key issue requirements for gas distribution capacities, environmental conditioning and oxygensystems.

1.2.3 Design and acceptance criteria including capacities for gas storage, choice of valves and fittings forcertain applications, environmental control parameters and breathing resistance for CCBS (if fitted).

1.2.4 Requirements for the design of oxygen systems aimed at reducing the hazards posed by flash fires.

1.2.5 Limitations on the use of hoses except hoses used in umbilicals are given.

1.2.6 Requirements to ensure safe arrangements in pressurised systems and control stations andrequirements for pipes, hoses, valves and fittings are given.

1.2.7 Requirements for shut off valves, pressure relief and drainage aimed at ensuring the safeguard ofpersonnel and plant, as are the requirements for alarm systems.

1.3 ApplicationThis section applies to all systems essential for the safe operation of the diving system.

1.4 References

1.4.1 Manufacturing standards applicable to individual components shall be supplementary to this standard.

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1.4.2 Further references are given to:

a) DNVGL-RU-SHIP Pt.4 Ch.6b) DNVGL-RU-SHIP Pt.5 Ch.10c) ISO 10524-1, Pressure regulators for use with medical gases, pressure regulators and pressure

regulators with flow metering devicesd) EN 10297-1, EN ISO 11114-3 and EN ISO 10297 (informative)e) EN ISO 4126-1 safety devices for protection against excesive pressure Part 1: Safety valvesf) ASTM G93-03 standard practice for cleaning methods and cleanliness levels for materials and equipment

used in oxygen-enriched environments.

1.5 Documentation requirementsLife support systems shall be documented as follows:

a) Plans showing schematic arrangement of all piping systems.b) Documents stating:

i) material specificationsii) maximum working pressureiii) dimensions and thicknessiv) contained fluidsv) type of valves and fittingsvi) specifications of flexible hoses.

c) Component lists, with specifications on make and type and documentation on any tests carried out onall equipment used in the life support system. Plans showing cross-section and giving particulars onmaterials and dimensions of umbilical.

d) Plans (diagrams) showing arrangement and giving specifications of the gas storage and supply (gasbanks, compressors, boosters etc.).

e) Plans showing the arrangement and giving specifications on environmental control systems andequipment (heating, CO2-absorption, circulation), diving crew facilities and drainage systems.

f) Determination showing the heat and cooling consumption for the system under specified environmentaltemperatures.

g) Description of proposed cleaning procedure for breathing gas system. Pipes, hoses, valves, fittings,compressors and umbilicals shall be documented as follows:

i) Plans and specifications showing suitability of the flexible hose in relation to its intended use. Forinformation, documentation of tests which have been carried out, as required.

ii) Plans and specifications giving particulars of umbilical conductors, minimum breaking load andminimum diameter of pulley and drums. For information, specification of max. design loads, elasticproperties and weight per unit length.

iii) Documentation of tests verifying the properties listed above and as required by K.


1.6.1 In addition to the test requirements here, detailed requirements are found in DNVGL-RU-OU-0375.

1.6.2 Testing during manufacture shall be in accordance with applicable manufacturing codes for theparticular component.

1.6.3 In systems conducting oxygen, all materials in contact with this gas shall be oxygen shock testedaccording to ISO 10524-1, pressure regulators for use with medical gases, pressure regulators and pressure

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regulators with flow-metering devices or equivalent standard applicable to the particular component. (See EN10297-1, EN ISO 11114-3 and EN ISO 10297 in informative references.)

1.6.4 For piping systems of copper, copper alloys and austenitic steels with chromium-nickel content above22%, the test can be waived.

1.6.5 Compressors shall be tested for the gas types and pressure intended. The tests shall incorporatemeasurements of humidity and possible, contaminants in the gas delivered.

1.6.6 Compressor components subjected to pressure shall be hydrostatic tested in accordance with thedesign code.

1.6.7 Closed circuit breathing system (CCBS, if fitted) shall be tested according to DNVGL-RU-OU-0375.

1.6.8 Flexible hoses shall be tested as specified in [6].

1.6.9 Umbilicals shall be tested as specified and as follows:

a) Each hose for use in umbilical shall be pressure tested to 1.5 times the design pressure before fitting inthe umbilical. After hose end fittings have been mounted, a gas leakage test to design pressure shall beperformed.

b) A pressure test to the design pressure of all hoses simultaneously and verification of the specifiedproperties by insulation tests of electrical conductors as well as impedance measurements of signalcables to specified properties shall be carried out.

c) Samples of the completed umbilicals shall be tested according to a manufacturer’s test programmecomplying with relevant requirements in the design code.

d) The test programme shall as a minimum include tensile testing and fatigue testing to 5000 load cycleswithout the umbilical showing any sign of permanent deformation of electrical conductors and orsignificant permanent deformations of other parts.

1.7 Survey and testing requirements during and after assembly

1.7.1 Hydrostatic testing of piping systems shall be in accordance with the technical requirements and as forcorresponding pipe class in breathing gas systems pertaining to class I piping systems.

1.7.2 Piping for the life support systems shall be pressure tested to 1.5 times the maximum workingpressure. Hydraulic systems may, however, be tested to the smaller of 1.5 times the maximum workingpressure, or 70 bar in excess of the maximum working pressure.

1.7.3 Piping systems conducting gas in life support systems shall be cleaned in accordance with an approvedcleaning procedure conforming to requirements given in ASTM G93-96 standard practice for cleaningmethods and cleanliness levels for materials and equipment used in oxygen-enriched environments.

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1.7.4 Piping systems intended to be used in breathing gas and oxygen systems shall be tested for purity inaccordance with requirements given in ASTM G93-96.The tests shall comprise:

a) measurement of contamination of the cleaning agent used at the last stage of the cleaningb) tests for possible traces of cleaning agents left in the piping system.

1.7.5 The gas storage and life support systems for gas shall be tested for leakage at low pressures and themaximum working pressure.

1.7.6 Life support systems for normal and emergency operation shall be tested for proper functioning.This includes:

a) sanitaryb) diver heating and cooling.

1.7.7 For the environmental control and monitoring system the failure conditions shall be simulated asrealistically as possible, if practicable by letting the monitored parameters pass the alarm and safety limits.Alarm and safety limits shall be checked.

1.7.8 For the automatic control systems the normal alterations of the parameters shall be imposed and thefunctions of the system tested. A copy of the approved test program shall be completed with final set pointsand endorsed by the surveyor.

1.8 Survey and testing requirements during and after installation

1.8.1 Support systems on-board the surface installations, significant for the safety of the diving system, arealso to be tested.

1.8.2 During the sea trials the normal launch and recovery system will be tested to the maximum depth. Forsurface diving systems employing a wet-bell the life support systems shall be checked for leakage.

1.9 Materials, including components for gases containing elevated oxygen levels

1.9.1 Piping systems containing gases with more than 25 per cent oxygen should be treated as systemscontaining pure oxygen.(See IMO code Of safety for diving systems Ch.2 design, construction and survey 2.5.15.)

1.9.2 The use of high-pressure oxygen piping should be minimized by the fitting of pressure reducingdevices, as close as practicable to the storage bottles.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.8.)The pressure in the oxygen systems shall be reduced at storage to the minimum pressure necessary forproper operation.

Guidance note:

A maximum pressure of 40 bar will normally be accepted.


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1.9.3 All materials used in oxygen systems should be compatible with oxygen at the working pressure andflow rate.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.7.)Materials and components fitted in oxygen systems shall be of types especially designed and tested for thispurpose.

1.9.4 Materials used in the breathing gas system shall not produce noxious, toxic or flammable products.

1.9.5 Oxygen and gases with an oxygen volume percentage higher than 25 per cent should be stored inbottles or pressure vessels exclusively intended for such gases.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.4.2.)

1.9.6 All components used in oxygen system shall be designed and oxygen shock tested based on EN ISO10297 (internal diameter of the test equipment shall be in line with the internal diameter of the test object)or other another acceptable international standard.

1.9.7 The minimum acceptable cleanliness level for components used in oxygen systems shall be ASTM LevelB (33 mg/m2) for nonvolatile residue (see DNVGL-RU-SHIP-Pt.5 Ch.10 Sec.6).

1.9.8 The metallic materials used in oxygen system shall be copper, copper alloys with copper content above55% and austenitic steels with chromium-nickel content above 22%.

1.9.9 The nonmetallic materials used in oxygen systems shall be oxygen shock tested for the applicablepressure range acc. EN ISO 15001.

1.9.10 Shut of valves shall be of the types which need several turns to close. On chamber penetrators, ballvalves may be accepted for emergency use only.

1.9.11 Pressure gauges in oxygen systems shall be designed and cleaned in accordance with EN 837-1.

1.9.12 Flexible metallic hoses made of austenitic steels with chromium-nickel content above 22% can beused for oxygen systems needs to be type approved. The oxygen shock test can be waived.

1.9.13 Flexible synthetic hoses can be used in systems with maximum pressure of 40 bar.Guidance note:

The material of the inner liner of the hose should be oxygen shock tested (as required in [1.9.6]) to the applicable workingpressure of 40 bar. The length of the flexible hose installed in the system may be longer than the length of the tested hose


1.9.14 If a lubricant is necessary to permit assembly operations or the functioning of a component, it shallbe selected from lubricants that have been found acceptable for use with oxygen and breathing gases forapplicable pressure range.

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2 Gas storage

2.1 Capacity

2.1.1 There shall be a permanently installed gas storage plant or suitable space for portable gas containers.The size of the containers or space shall be sufficient to provide the divers with adequate quantities of gasesfor operation at maximum operating depth for both normal and emergency modes.

2.1.2 The minimum gas storage capacity of fixed installed gas containers or space for portable gascontainers intended for emergency operations shall be sufficient to:

a) Pressurise the inner area twice and the transfer compartments once more to maximum depth, dmax, withsuitable breathing gas, and ventilate the chamber as required.

b) maintain a proper oxygen partial pressure in the inner area and supply for masks for at least 24 hours.For pure oxygen, the minimum volume may be taken as 2 Nm3 for each diver where 1 Nm3 is given as 1cubic metre of the gas at 0°C and 1.013 bar standard condition.

c) Conduct two emergency dives to dmax.

2.1.3 For emergency use of masks required by [2.1.2] b) there shall be sufficient facilities to supplyadequate quantities of gases. The facilities shall be capable of providing a relevant delivery rate both atmaximum depth and during decompression. Adequate quantities shall be determined for the applicableoperation, but not less than 2 m3 at the pressure of the inner area with an oxygen partial pressure between0.18 and 1.25 bar for each diver.

2.1.4 The storage capacity for emergency gas shall be provided in separate containers, and shall not beincluded in the containers for current gas supply.

2.1.5 If applicable, the wet-bell shall have self-contained emergency gas storage with a minimum capacity tosupply the divers for the duration of their in-water stops prior to surfacing.

2.2 Shut-off, pressure relief and drainage

2.2.1 All surface compression chambers and diving bells which may be pressurized separately should befitted with overpressure alarms or pressure relief valves. If pressure relief valves are fitted, a quick-operatingmanual shut off valve should be installed between the chamber and the pressure relief valve and should bewired opened with a frangible wire. This valve should be readily accessible to the attendant monitoring theoperation of the chamber. All other pressure vessels and bottles should be fitted with a pressure relief device.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.5.)

2.2.2 Pressure vessels shall be fitted with over pressure relief devices and shut off valves.

2.2.3 Pressure vessels without individual shut-off valves and with:pV < 50, installed in groups with a totalpV < 100, can have a common overpressure relief device and shut-off valve.p = design pressure in barV = volume in m3 (standard conditions)

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2.2.4 For gas storage of breathing gases and oxygen, the pressure relief device shall be a safety valve.Safety valves shall be set to open at a pressure approx. 3% above the developed pressure at 55°C, basedon filling the cylinders at 15°C to maximum filling pressure. The total relieving capacity shall be sufficient tomaintain the system pressure at not more than 110% of design pressure. Developed pressure under above-mentioned conditions may be taken as given in reference to a standard such as EN 13096 transportable gascylinders conditions for filling gases into receptacles single component gases or EN 13099 transportable gascylinders conditions for filling of gas mixtures into receptacles.

2.2.5 Containers where water can accumulate shall be provided with drainage devices. (E.g. volume tanksand filters).

3 Gas distribution and control system

3.1 General

3.1.1 Each surface compression chamber and diving bell should be fitted with adequate equipment forsupplying and maintaining the appropriate breathing mixtures to its occupants at all depths down tomaximum operating depth. When adding pure oxygen to the chamber, a separate piping system should beprovided.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.1.)

3.1.2 In addition to the system mentioned in [2.6.1] each surface compression chamber (-omitted, non-applicable text-) should contain a separately controlled built-in breathing system for oxygen, therapeuticgas or bottom mix gas with at least one mask per occupant stored inside each separately pressurizedcompartment and means should be provided to prevent any dangerous accumulation of gases.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.2.)In addition to the above stipulated masks, there shall be one spare mask installed in each compartment.

3.1.3 The gas distribution system consists of all components and piping necessary for distribution of gas fornormal and emergency operations.

3.1.4 Piping for gas and electrical cables shall be separated.

3.1.5 Filters and automatic pressure reducers shall be so arranged that they can be isolated withoutinterrupting vital gas supplies.

3.1.6 Valves in piping systems to masks, and divers in water shall be so arranged that:

a) leaking valves cannot cause unintentional gas mixturesb) oxygen cannot unintentionally be supplied to other piping systems than that intended for oxygen.

3.1.7 Gases vented from the diving system should be vented to the open air away from sources of ignition,personnel or any area where the presence of those gases could be hazardous.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.13.)

3.2 Control stands

3.2.1 Requirements for instrumentation are given in Sec.7.

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3.2.2 The control stands shall have means for:

a) choice between gas storage containersb) pressurising and pressure regulation of each compartment independentlyc) decompression of each compartment independentlyd) equalising the pressure between compartmentse) controlling oxygen and mix gas supply to masks in each individual compartmentf) controlling gas supply to the divers and the wet-bell if applicable.

3.3 Basket and wet-bell (if wet-bell is employed)

3.3.1 The diving bell should be designed with a self-contained breathing gas system capable of maintaining asatisfactory concentration of breathing gas for the occupants for a period (-omitted, non-applicable text-) atits maximum operating depth.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.3.)

3.3.2 There shall be two independent supplies of gas to the divers and, if applicable, the wet-bell umbilical.

3.3.3 The diver(s) shall have, in addition to their normal umbilical supply, an independent self-containedemergency supply from the basket or wet-bell. The emergency supply in a basket may be by means ofreduced air from a cylinder mounted in the basket.

3.3.4 The breathing gas system supplying the personal umbilical to the stand-by diver in the wet-bell, whenwet-bell is employed, shall be arranged for an alternative supply, independent of the lock-out diver(s)'snormal supply. The wet-bell’s on-board gas supply may be accepted for this purpose.

3.3.5 The wet-bell, if employed, shall be equipped with a valve operated exhausts and shall be fitted with aspring-loaded valve that closes when the valve handle is released.

3.3.6 The wet-bell shall be equipped with masks corresponding to the number of divers plus one. The masksshall be arranged for supply from normal and emergency supply alternatively. Diving masks and divinghelmets with gas supply are accepted as masks.

3.4 Chambers

3.4.1 The distribution system to each compartment shall facilitate:

a) two independent alternatives for pressurisation with a minimum pressurisation rate of 2 bar/minute to 2bar and at 1 bar/minute thereafter

b) depressurisation with a decompression rate in accordance with specified decompression tables (e.g. USNAVY diving tables)

c) maintenance of a suitable breathing atmosphere in the inner aread) supply of suitable breathing gas for maskse) exhaust from masks intended for oxygen if a closed circuit breathing gas system is not used.

3.4.2 Each compartment shall be equipped with breathing masks corresponding to the maximum number ofdivers for which the chamber is rated plus one. Other compartments shall have at least 2 masks.

3.4.3 The masks shall be permanently connected or easily connectable to piping systems for supply of thegases according to [2.1.3].

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3.4.4 The exhaust sides of the masks intended for oxygen shall be connected to external dump, or to be of aclosed circuit type.

3.4.5 The mask systems shall be secured against inadmissible pressure drop on the exhaust side.

3.4.6 The gas supply system shall be arranged to ensure homogenous gas content in the inner area.

3.5 Stand-by diver at surfaceA system for supply of life support to a stand-by diver at surface shall be arranged independent from thedivers' supply, and shall meet the requirements for the normal diver’s supply.

3.6 Nitrogen/oxygen mixing systems for direct supply for breathing

3.6.1 Systems for mixing of nitrogen and oxygen for subsequent direct supply for breathing shall beautomatic, to have an automatic control system, an automatic alarm system and an automatic safetysystem.

3.6.2 The safety system shall be independent of the control system and shall incorporate changing of thesupply automatically to a premixed suitable breathing gas if tolerances are exceeded. The safety system shallensure a constant delivery of suitable breathing gas to the diver during all operating conditions, taking intoaccount the characteristics of components in the systems such as response time for gas analysers etc.

3.6.3 As an alternative to [3.6.2], the inclusion of a large volume tank is considered to provide an equivalentlevel of safety as that prescribed by the requirements for 'automation' and 'independence'. The remainingrequirements shall be met. The volume tank shall be such that the prescribed tolerances for partial pressuresdownstream are not deviated from within the first hour after the analysers have alerted the operator that theupstream mixture is out of the tolerated range. The Alarm shall be audio-visual at a manned control station.

3.6.4 The control system shall keep the mixture at a pre-set value within prescribed tolerances. Maximumtolerances: +/- 0.03 bar, partial pressure O2.

3.6.5 If the mixing system is arranged as a closed circuit breathing system (CCBS), it shall meet therequirements for such systems given in Ch.3 Sec.3.

4 Diver’s heating and environmental conditioning in chambers

4.1 GeneralA diving system should include adequate plant and equipment to maintain the divers in safe thermal balanceduring normal operations.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.7.)

4.2 Heating of divers in the water

4.2.1 Divers may employ insulated suits and not require active heating. In this case, calculations, or vendorinformation, shall be submitted for information.

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4.2.2 When required, the divers shall have a normal heating system with controls and capacity sufficientto maintain given temperatures for the divers in the water according to specified diving tables. The heatingsystem shall be fitted with a temperature indicator.

4.3 Heating and cooling of chambers

4.3.1 Systems for heating and cooling of the living compartments shall be arranged when required accordingto environmental criteria given in the specifications.

4.3.2 Heating/cooling coils on the outside of the chambers shall have a minimum of two independenttemperature controls of the power circuit.

4.4 Noise reduction

4.4.1 Pipe systems should be so designed as to minimize the noise inside the diving bell and surfacecompression chamber during normal operation.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.1.)

4.4.2 Silencers shall be fitted and the system shall be so designed that the divers cannot be exposed toharmful noise levels.

Guidance note:

IMO resolution A.468 (XII) code on noise levels on-board ships.


4.4.3 Silencers shall be fitted with shields which provide protection against possible fragmentation but whichdo not affect the gas flow.

4.5 Gas circulation systems for chambers

4.5.1 Internal circulation systems for gas in the chambers shall be such that homogeneous gas content isensured.

4.5.2 Pressurising and exhaust systems shall be arranged to ensure an even mixing of gas.

4.5.3 The circulation system shall have sufficient capacity to maintain a homogenous gas mix at the setoperational parameters.

4.5.4 Materials shall be considered for toxic or noxious properties.

4.6 Removal of carbon dioxideCarbon dioxide removal systems shall be arranged for each living compartment and shall have the capacityto maintain the partial pressure of carbon dioxide below 0.005 bar continuously based on a production rateof 0.05 Nm3 per hour per diver. For two divers’ occupancy, this requirement may be met by flushing thechamber atmosphere providing the maximum noise levels are not exceeded.

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5 Piping systems

5.1 General

5.1.1 All high-pressure piping should be well protected against mechanical damage.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.14.)

5.1.2 Piping systems shall comply with the technical requirements for class I piping systems in DNVGL-RU-SHIP Pt.4 Ch.6.

5.1.3 Welding of joints shall be carried out by qualified welders using approved welding procedures andwelding consumables. Technical requirements are given in DNVGL-RU-SHIP Pt.2 Ch.2.

5.1.4 Threaded pipe penetrations are only acceptable for internal diameters less than 20 mm.

5.1.5 Where applicable the following requirements given in DNVGL-RU-SHIP Pt.4 Ch.6, shall be followed:

a) bending and welding proceduresb) welding joint particularsc) preheatingd) heat treatment after welding and forminge) non-destructive testing and production weld testingf) bracing of copper and copper alloys.

5.1.6 Piping systems which may be subjected to a higher pressure than designed for should be fitted with apressure relief device.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.6.)

5.1.7 Low-pressure systems supplied from high-pressure system shall be provided with pressure reliefvalves. The total relieving capacity shall be sufficient to maintain the system pressure at not more than110% of design pressure. The relief device shall be located adjoining, or as close as possible, to the reducingvalve.

5.1.8 All systems shall be provided with means of manually relieving the pressure.

5.1.9 Filters shall be provided on the high-pressure side of gas systems.

6 Hoses

6.1 General

6.1.1 Flexible hoses, except for umbilicals, should be reduced to a minimum.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.9.)

6.1.2 Flexible hoses shall not replace fixed piping.

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6.1.3 In addition to umbilicals, short lengths (up to 2 m) of flexible hose may be used when necessaryto admit relative movements between machinery and fixed piping systems. For assemblies incorporatingspecially approved hoses and securing arrangements, lengths up to 5m may be permitted if fixed piping isnot practicable. In such cases, securing arrangements shall be in place at 1m intervals of the length of thehose. In addition to the couplings, the hoses shall be secured in such a way as to prevent the hose from whiplashing in the event that the coupling fails. When applicable, couplings shall incorporate bends so that kinksin the hoses are avoided.

6.1.4 Flexible hoses with couplings shall be certified.

6.1.5 Flexible metallic hoses with permanently fitted couplings shall be certified.

6.1.6 Bursting pressure of synthetic hoses shall be at least:

a) Hoses for fluids: 4 times the maximum working pressure.b) Hoses for gases: 5 times the maximum working pressure.

6.1.7 Hot water hoses shall be designed for conveyance of fluids of temperatures not less than 100°C.

6.1.8 Flexible metallic hoses shall not be installed in systems subject to excessive vibrations or movements.

7 Valves

7.1 Valve design

7.1.1 Pressure ratings for valves shall be in accordance with a recognised national standard.

7.1.2 Design and arrangement of valves shall be such that open and closed positions are clearly indicated.

7.1.3 Valves are normally to be closed by clockwise rotation.

7.2 Chamber valves

7.2.1 Exhaust lines should be fitted with an anti-suction device on the inlet side.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.12.)

7.2.2 All pipe penetrations on chambers should be fitted with two shut off devices as close to the penetrationas practicable. Where appropriate, one device should be a non-return valve.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.4.)

7.2.3 All pipe penetrations in the chambers shall be fitted with external and internal shut-off valves mounteddirectly on the shell plating. Valves may be mounted close to chamber shells, provided that the pipingbetween the chamber and valve is well protected and has a minimum thickness according to DNVGL-RU-SHIP.

7.2.4 In addition to the requirements in [7.2.3] all penetrations for lines designed for gas distribution (e.g.supply, exhaust and equalisation) shall be fitted with non-return valves or flow fuses as appropriate for thedirection of gas flow. Lines specifically designed for non-distribution purposes (e.g. analysis) shall be kept tothe minimum internal diameter possible and limited to a maximum of 5 mm.

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7.2.5 The piping between externally mounted non-return valve or flow-fuse and the external shut-off valveshall be well protected and have minimum thickness according to [5].

7.2.6 The compartments shall be fitted with a safety relief valve or a visual and audible overpressurealarm alerting the operators at the control station. National standards and/or regulations may stipulaterequirements for safety relief valves, and shall be followed in these cases.

7.2.7 Penetrations for safety valves shall be provided with shut-off valves on both sides of the shell plating.These shut off valves shall be sealed in the open position. Any safety valves shall be set to open at apressure of approx. 3% above the design pressure.

7.2.8 Valves in chambers designed for holding water (i.e. hyperbaric training centres) shall be considered ineach case.

8 Fittings and pipe connectionsBite and compression type couplings and couplings with brazing, flared fittings, welding cones and flangeconnections are only allowed for piping up to 25 mm (1") and shall be designed according to a recognisedstandard.

9 Pressure regulators

9.1 General

9.1.1 Pressure regulators shall have more than one full rotation from fully closed to fully opened position.

9.1.2 Automatic pressure reducers for breathing apparatuses shall be fitted.

10 Compressors for breathing gas systems

10.1 General

10.1.1 Compressors shall be certified.

10.1.2 Compressors shall be equipped with all the accessories and instrumentation which are necessary foreffective and dependable operation.

10.1.3 Compressors shall be designed for the gas types and pressure rating as specified by the operationand so designed that the gas is protected against contamination by lubricants.

10.1.4 Suitable protection shall be provided around moving parts, and the safety relief valves shall exhaustto a safe place.

11 Purification and filter systems

11.1 General

11.1.1 Purification and filter systems shall be certified.

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11.1.2 The content of contaminants in the breathing gas after the filter system shall not exceed theacceptance criteria given in EN 12021 or equivalent standards. National requirements remain unaffectedhereby.

11.1.3 Where breathing gas is supplied directly from running compressors, an automatic shut off devicefor the compressor shall be installed to shut it down when the purification/filter system have reached anunacceptable level of contamination.

11.1.4 Where breathing gas is supplied directly from running compressors, a mean of analysing thebreathing gas for carbo monoxide shall be provided for continuos monitoring, incorporating an audio/visualalarm.

11.1.5 Filter housings, casings, breathing gas receivers and other parts subject to pressure shall behydrostatically tested in accordance with national and international design codes.

11.1.6 Additional requirements to external environment in terms of toxic (H2S and hydro carbon) gas (seeDNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [1.9]).

12 Umbilicals

12.1 GeneralUmbilicals shall be designed, tested and certified in accordance with relevant sections of the most recentedition of ISO 13628-5 petroleum and natural gas industries, design and operation of subsea productionsystems, part 5: subsea control umbilicals. The relevant sections of the standard shall be agreed in acompliance matrix when the signed request for certification of the umbilicals is received by DNV GL.

12.2 HosesHoses for umbilicals shall comply with the requirements given in [6]. Hoses intended for operation witha larger external pressure than the internal pressure, shall be able to withstand 1.5 times this pressuredifference without collapsing or shall be able to collapse without signs of permanent deformation.

12.3 Electrical cables

12.3.1 Electrical cables for umbilicals shall comply with requirements given for umbilicals in Sec.4.

12.3.2 The minimum average thickness of insulating walls and temperature classes shall be in accordancewith DNVGL-RU-SHIP Pt.4 Ch.8.

12.4 SheathingAny sheathing of a compact umbilical shall be of a design which avoids build-up of an inside gas pressure inthe event of a small leakage from a hose.

12.5 Strength membersThe strength members of umbilicals shall have sufficient stiffness to avoid plastic yielding of electricalconductors at design load, and shall be properly secured.

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SECTION 4 ELECTRICAL SYSTEMS

1 Introduction

1.1 ObjectivesThe objectives of this section are to emphasise the special needs associated with the design and manufactureof surface diving systems. General requirements for electrical systems and components are given in DNVGL-OS-D201.

1.2 Scope

1.2.1 The key issues are identified in:

a) the service definitions by defining essential, emergency and non-important services in Sec.1 [4]b) the power supply systems and capacity by specifications for emergency supplyc) cables and penetratorsd) documentation requirements.

1.2.2 Material specification is included for insulation of cables in the inner area.

1.2.3 Design criteria for electrical penetrators are outlined. Philosophy on earthing is specified, in that hullreturn is not allowed.

1.3 Application

1.3.1 This section applies to all surface diving systems.

1.3.2 This section bears impact on Sec.3, Sec.5, Sec.6, Sec.7 and Sec.8.

1.4 References

1.4.1 Recognised production standards include those provided by the International Electro technicalCommission (IEC).

1.4.2 The following codes and standards are applicable:

a) DNVGL-OS-D201b) relevant IEC equipment construction and design standards referred toc) IMCA code of practice for the safe use of electricity underwater.

1.5 Documentation

1.5.1 A system philosophy with general arrangement and where the equipment is placed shall be submittedearly on in the project.

1.5.2 Single line distribution system diagrams for the whole installation. The diagrams shall give informationon full load, cable types and cross sections, and make, type and rating of fuse- and switchgear for alldistribution circuits.

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1.5.3 Calculations on load balance, including emergency consumption and battery capacities.

1.5.4 Complete multi-wire diagrams, preferably key diagrams, of control and alarm circuits for all motors orother consumers.

1.5.5 A list of ALARMS and monitoring parameters shall be submitted for information.

1.5.6 Plans showing arrangements of batteries with information about their make, type and capacity.

1.5.7 Plans showing arrangement and single line diagrams of the communication system.

1.5.8 Complete list of components and documentation on any tests carried out on all electrical equipment tobe permanently installed within the chamber, and the wet-bell (if applicable).


1.6.1 A test for insulation resistance shall be applied to every circuit between all insulated poles and earth,and between individual insulated poles. A minimum value of 1 mega-ohm shall be attainable.

1.6.2 Main and emergency power supplies shall be tested.

1.6.3 Electrical penetrators shall be tested at the manufacturers as specified below. Tests shall be madebetween each conductor and screen and tests shall be carried out on penetrators from the same productionbatch. The tests shall be carried out in the sequence they are listed. The penetrators shall show no sign ofdeficiency during and after the testing.

1.6.4 Tests to be carried out include:

a) a voltage test, by applying 1 kV plus twice the design voltage for 1 minute between each conductor andscreen separately

b) a hydrostatic test to a pressure of twice the design pressure, repeated 5 timesc) a gas leakage test with the cables cut and open with air to twice the design pressured) an insulation test to 5 Megaohms at the design pressure, applying saltwater.

1.7 Survey and testing requirements during and after assemblySurvey and testing during and after assembly shall be carried out according to an approved inspection andtest procedure proposed by the builder in compliance with applicable requirements in DNVGL-OS-D201 Ch.2Sec.10 [4] inspection and testing.


1.8.1 Survey and testing during and after installation shall be carried out according to an approvedinspection and test procedure proposed by the builder in compliance with applicable requirements in DNVGL-OS-D201 Ch.2 Sec.10 [4] inspection and testing.

1.8.2 During the sea trials the normal launch and recovery system will be tested to the maximum depth. Forsurface diving systems employing a wet-bell the electrical systems shall be checked for proper function.

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1.9 Markings and signboardsMarkings and signboards according to DNVGL-OS-D201 Ch.2 Sec.3 [5].

1.10 MaterialsMaterials shall comply with DNVGL-OS-D201.

2 System design

2.1 Design principles

2.1.1 The electrical systems and installations supplying essential, emergency and normal services related tothe divers and or the diving operation, shall meet the requirements for such services as defined in Ch.1 Sec.1[5],

2.1.2 Electrical circuits and equipment used in water shall be considered in each separate case and inaccordance with IMCA D 045, R015 code of practice for the safe use of electricity underwater. Provisions shallbe made to reduce the possible fault currents, to which a diver can be exposed, to a harmless level.

2.1.3 The location of rechargeable battery installations are considered a hazardous area and shall becarefully considered during the conceptual design of the diving system lay-out early in the project, incompliance with DNVGL-OS-D201 Ch.2 Sec.2 [9.4].

2.2 System voltagesFor installations within the inner area (see definitions under Ch.1 Sec.1 [2.3]), the following maximumsystem voltages are permitted:

a) The chamber:

i) For power and heating equipment: max. 250 V A.C. if protected against accidental touching orinsulation failures and fitted with a trip device.

ii) For lighting, socket outlets, portable appliances and other consumers supplied by flexible cables andfor communication and instrumentation equipment: max. 30 V D.C. These systems shall be suppliedby isolating transformers.

b) The wet-bell (when applicable):

i) For all electrical equipment, voltages will be accepted up to max 30 V D.C., and shall be supplied byisolating transformers.

ii) Higher voltages than specified above may be acceptable upon special consideration, providedadditional precautions are taken in order to obtain an equivalent safety standard, e.g.: by use ofearth fault circuit breakers.

2.3 Main electric power supply systemThe electrical systems and installations supplying essential services related to the divers and or the divingoperation as defined in Sec.1 [4], shall be supplied from a main and an emergency or transitional source ofpower as required by DNVGL-OS-D201.

2.4 System functionality and design

2.4.1 The distribution system shall be such that, the failure of any single component cannot influence or setother services out of function for longer periods.

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The capacity of the main source of power shall be able to provide power to all normal and essential servicesaccording to Ch.1 Sec.1 [5], and shall be included in the services to be supplied by the main source of poweras described in DNVGL-OS-D201 Ch.2 Sec.2 [2] and interpreting SOLAS reg. II-1/40.1.1.

2.4.2 The capacity of emergency source of power shall be able to provide power to all emergency servicesaccording to [5], and shall be included in the services to be supplied by the emergency source of power asdescribed in DNVGL-OS-D201 Sec2 [3] and interpreting SOLAS reg. II-1/43.2.

2.4.3 The emergency source of power and the emergency power distribution shall be capable of handlingpeak loads.

2.4.4 Power supplies required for the operation of life support systems and other essential services shall besufficient for the life-support duration in order to cater for safe termination of the diving operation.

2.4.5 Each compression chamber shall be provided with a main and emergency source of lighting sufficientfor the life-support time and of sufficient luminosity to allow the occupants to read gauges and operateessential systems within the chamber. Ingress of adequate light through the windows may be accepted asemergency lighting when appropriate.

2.5 Emergency power supply system

2.5.1 In the event of failure of the main source of electrical power supply to the diving system anindependent source of electrical power should be available for the safe termination of the diving operation.It is admissible to use the ship's emergency source of electrical power as an emergency source of electricalpower if it has sufficient electrical power capacity to supply the diving system and the emergency load for thevessel at the same time.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.2.)

2.5.2 The alternative source of electrical power should be located outside the machinery casings to ensure itsfunctioning in the event of fire or other casualty causing failure to the main electrical installation.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.3.)

2.5.3 The diving system shall have a source of emergency power and an emergency power supply systemindependent of the main source of power and the main power supply system, as required by DNVGL-OS-D201 that outlines the SOLAS reg. II-1/43 part D requirements.

2.5.4 The emergency source of power shall be a self-contained, independent source of power. It shallimmediately supply at least those services specified as emergency consumers in Sec.1 [4] and shall beeither:

a) a generator, driven by a suitable prime mover, orb) an accumulator battery, orc) the ship's emergency switchboard, ord) a combination of the above.

2.5.5 Where this source of power is a generator, it shall be started automatically upon failure of theelectrical supply from the main source and shall be automatically connected within 45 sec., thereby providingemergency services.

2.5.6 Where this source of power is an accumulator battery, it shall be automatically connected to anemergency power supply system in the event of failure of the main source of electrical power. It shall be

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capable of carrying the maximum emergency load for a time specified under [5] without excessive voltagedrop, carrying the emergency electrical load without recharging while maintaining the voltage of the batterythroughout the discharge period within 12% above or below its nominal voltage.

2.6 Transitional source

2.6.1 The following consumers shall be provided with transitional power (oninterrupted power supplies):

a) condition monitoring of emergency batteriesb) emergency lighting, including external strobe lighting on basket/wet-bellc) emergency communicationd) alarm systems for the emergency services.

2.6.2 If other emergency consumers must be available in the switchover period from main to emergencypower, either for operational reasons or to avoid malfunction of the service, a transitional power source(battery backup) for these consumers shall be provided. The capacity of this transitional power shall beminimum 30 minutes. (See SOLAS reg. II-1/43 part D para.4.)

2.7 Battery systems

2.7.1 Batteries shall not normally be installed within the inner areas in the chambers.

2.7.2 Battery housings shall be provided with adequate and unobstructed ventilation to open air inaccordance with DNVGL-OS-D201 Ch.2 Sec.2 [9.4], so that an accumulation of generated flammable gasesis avoided. The ventilation intake shall be fed into the lower parts and the outlet arranged in the uppermostpart of the housing.

2.8 Electric power distribution

2.8.1 All switchboards shall be designed, constructed, tested and certified in accordance with therequirements given in DNVGL-OS-D201.

2.8.2 If the main power to the diving system is supplied from a distribution board, this board shall have twoindependent supply circuits from different sections of the main switchboard or separate power supplies.

2.8.3 Control gear in the inner area shall normally not be fitted. However, special arrangement may beacceptable after consideration in each case, based on special precautions.

2.8.4 Devices for easy disconnection of all electrical installations in the decompression chambers in anemergency situation shall be fitted. These devices shall be located on the control stand. It shall be possible todisconnect each chamber separately.

2.8.5 Emergency circuits wiring is considered to be an essential component in the diving system and shalltherefore be fire proofed in accordance with the requirements in Sec.1 [6.4] when supplies are sourced fromoutside the outer area.

Guidance note:

Allowances are given to IEC 60331 cables protected by A0 division trays or piping.


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2.8.6 Fuses or circuit breakers shall not be installed within chambers and wet-bells, except for emergencybattery powered supply circuits.

Guidance note:

Installation inside may be arranged as mentioned above, however, fuse-gear shall not be operable by divers


2.9 LightingEach surface compression chamber and diving bell should have adequate means of normal and emergencylighting to allow an occupant to read gauges and operate the system within each compartment.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.4.)

3 Equipment in general

3.1 General requirements

3.1.1 All electrical equipment and assemblies shall be designed and arranged in order to minimise the riskof fire, explosion, electrical shock, emission of toxic gases to personnel, and galvanic action of the surfacecompression chamber or wet-bell.

3.1.2 The electric power supply arrangement shall be designed to minimise the risk of electrical capacitydepletion as a result of a fault.

3.2 Environmental requirements

3.2.1 All electrical equipment and installation, including power supply arrangements, should be designedfor the environment in which they will operate to minimize the risk of fire, explosion, electrical shock andemission of toxic gases to personnel, and galvanic action of the surface compression chamber or diving bell.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.1.)

3.2.2 The electrical equipment and installations, including power supply arrangements, shall be constructedand installed to operate satisfactorily under all environmental conditions for which the diving system isdesigned. See DNVGL-OS-D201 Ch.2 Sec.2.

3.2.3 Electrical equipment within the compression chamber shall be designed for hyperbaric use, oxygen-enriched atmospheres, high humidity levels and marine application. See:

a) DNVGL-OS-D201b) NFPA53M (National Fire Protection Agency) manual on fire hazards in oxygen-enriched atmospheres

1990c) IMCA D 045 code of practice for the safe use of electricity underwaterd) IMCA D 041 use of battery operated equipment in hyperbaric conditions.

3.2.4 All materials of submerged systems shall be such that their electrical and mechanical properties arenot influenced by water absorption.

3.3 Termination and cable penetrations

3.3.1 All electrical penetrators in pressure containing structures shall be purpose designed, certified and shallbe arranged with separate fittings.

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3.3.2 Penetrators in pressure vessels shall be of the sleeve passing hull penetration types. They shall be gasand water-tight even in the event of damage to the connecting cables.

3.4 Earthing

3.4.1 Electrical systems with hull return shall not be applied. Electrical distribution systems shall haveinsulated neutral (IT).

3.4.2 All pressure vessels for human occupancy (PVHOs) shall be provided with earthing connection devicesfor external main protective earth bonding.

3.4.3 In the water, all metal enclosures shall be earthed by means of a copper earth conductor incorporatedin the supply cable, with cross-section at least of the same size as the supply conductors and not less than1 mm2. For cables having metal wire braid or armour this may alternatively be used as earth conductor,provided that the braiding cross section is sufficient.

3.5 Insulation

3.5.1 Each insulated supply system, including the secondary side of step-down or isolating transformers (orconverters) shall be provided with an automatic insulation monitoring device, actuating switch-off and alarmby insulation faults. Alarm only may be used if a sudden switch-off of the equipment may cause danger forthe divers. This insulation monitoring shall be continuous.

3.5.2 The indicator shall be located at the control stand.Guidance note:

Protection against insulation failures may be achieved by double insulated apparatus or earth fault circuit breakers.


4 Miscellaneous equipment

4.1 General

4.1.1 Electric motors placed in the inner area shall be provided with overload alarms or be inherently safe.The alarms may be initiated by over current, or by temperature detector in the motor itself. The normal overcurrent protections (short circuit protection) on the motors shall also be in place.

Guidance note:

The requirement provides safety against overheating, with the possible development of toxic gasses, and or danger of flash firein oxygen enriched environments. In special cases there may be other risks involved in overheating of the motors. However, ifthe motor is considered inherently safe, the requirement for the overload alarms may be revoked. This is considered preferable incases where the number of alarms should be kept at a minimum so as to avoid stressful operating conditions and or confusion.


4.1.2 Pressure resistant enclosures in the inner area or on the wet-bell shall be designed for 1.3 times thedesign pressure of the diving system. Tests shall be carried out with gas or water as applicable.

4.2 Lighting equipment – inner areaProtection against possible bursting of electrical bulbs shall be in place.

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5 Cables

5.1 Application

5.1.1 Cables for use in the outer area shall comply with DNVGL-RU-SHIP Pt.4 Ch.8. All cables shall have anearthed braiding or screen around the conductors and be equipped with an insulating outer sheet.

5.1.2 Cables for use in the inner area shall comply with the requirements in [5.1.1] above, with exceptionto the materials used. The materials shall be designed for the purpose of being installed into a hyperbaricatmosphere. The cables in the inner area shall be halogen free and shall not give off toxic, noxious orflammable gases even when overheated. Dismantled ends of insulated conductors shall be protected withsleeves of a non-combustible material (e.g. glass fibre weave). Ordinary ship cables with insulation of ahalogenated material (e.g. P.V.C.) shall not be accepted. Synthetic insulation materials based on P.T.F.E.(Polytetrafluoroethylene) may be accepted.

5.1.3 Flexible cables for transmission of electrical power and signals from the surface support to the divers inthe water and the wet-bell shall be constructed as dry-core cable (i.e. water shall not reach the insulation ofthe individual conductors).

5.1.4 The submerged cables shall be able to withstand an external hydrostatic pressure of 1.3 times theactual external pressure.

5.1.5 Unless installed in pipes, electrical cables shall be readily accessible for visual inspection.

5.1.6 Tensile loads shall not be transferred to the electrical cables.

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SECTION 5 FIRE PREVENTION, DETECTION AND EXTINCTION

1 Introduction

1.1 ObjectiveThe objectives of this section are to specify additional requirements for fire protection serving surface divingsystems. General requirements for fire protection are given in DNVGL-OS-D301.

1.2 ScopeKey issues are identified through requirements for materials, insulation and separation from adjacent spaces,sprinkler systems and extinction agents. Reductions of hazards are ensured through these issues.

1.3 Application

1.3.1 These requirements apply to all surface diving systems. However, some systems may be located onopen deck. In these cases the requirements for insulation against adjacent spaces and requirements forsprinkler systems may be more lenient.

1.3.2 This section bears impact on Sec.4 (build-up of static electricity, degree of protection provided byenclosure IP for equipment on chambers covered by sprinkler systems, power to alarms) and Sec.8.

1.4 References

1.4.1 For quantitative design parameters and functional requirements,see relevant standards and guidelines,including DNVGL-OS-D301.

1.4.2 In addition supplementary information is found in the National Fire Protection Agency codes' chapterson hyperbaric systems and oxygen enriched environments.

1.4.3 Requirements applicable to the support vessel are given in SOLAS.

1.4.4 See:

a) IMO res. MSC.61(67) (FTP code)b) DNVGL-ST-OS-A101 Ch.2 Sec.3 safety principles and arrangementsc) IMO res. MSC/Circ.848 MSC.98(73) (FSS code).

1.5 Documentation requirementsFire prevention, detection and extinction shall be documented as follows:

a) A List of all materials to be installed in the inner area, where possible with data on and or evaluation offlammability in conditions under which the materials can be used.

b) Plans and specifications of fire detection, fire alarm and fire extinction equipment for both the inner andouter area.

1.6 Survey and testing requirements during and after assemblyThe fire detection, fire alarm and fire extinction systems in the inner areas shall be tested for proper functionaccording to specifications.

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1.7 Materials

1.7.1 All materials and equipment used in connection with the diving system should be, as far as isreasonably practicable, of fire-retardant type in order to minimize the risk of fire and sources of ignition.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.1.)

1.7.2 The use of combustible materials shall be avoided wherever possible. Combustible materials includematerials which may be brought to explode, or burn independently in the resulting gas environment,applicable to the outer area air at a pressure of 1 bar or the inner area at applicable gas mixtures andmaximum pressure.

1.7.3 Structural components, furniture and knobs, paints, varnishes and adhesives applied to these,shall be of non-hazardous materials., i.e. they shall be tested in accordance with relevant parts of IMOres.MSC.61(67) (FTP code) or other acknowledged standard.

Guidance note:

In order to comply with [1.5], materials for use in inner area should be tested at an elevated pressure. Where such materials arenot available, fitting a fixed fire extinguishing system in the inner area may be considered as an alternative.


1.7.4 Materials and arrangements shall, wherever possible, be made so as to avoid build-up of staticelectricity and to minimise the rise of spark production due to electrical failures or combination of materials.In inner areas without electrical equipment, the furniture and floors of electrically conductor materials maybe used. For inner areas where electrical equipment is used, the materials and arrangements shall be madeso as to minimise faulty contact with earthed metalwork.

2 Fire protection

2.1 ArrangementWhen applicable, control rooms for surface diving systems located in hazardous zone 2 shall comply with therequirements given in DNVGL-OS-A101 Ch.2 Sec.3 safety principles and arrangements.Other control stands, essential to the function of the diving system, shall be protected such that the controlsmay be maintained whilst the divers are being evacuated in the event of a fire.

3 Fire detection and alarm system

3.1 Outer area

3.1.1 Interior spaces containing diving equipment such as surface compression chambers, diving bells,gas storage, compressors and control stands should be covered with an automatic fire detection and alarmsystem and a suitable fixed fire-extinguishing system.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.3.)

3.2 Inner areaThe inner area shall be equipped with automatic fire detection and alarm system complying with DNVGL-OS-D301. The section or loop of detectors covering the inner area shall not cover other spaces.

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3.3 Fault detectionProvisions shall be made for warning of faults, e.g. voltage failure, broken line, earth fault, etc., in the firealarm and detection system.

4 Fire extinguishing

4.1 Inner area

4.1.1 Each compartment in a surface compression chamber should have a suitable means of extinguishing afire in the interior which would provide rapid and efficient distribution of the extinguishing agent to any partof the chamber.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.6.)

4.1.2 The inner area shall be equipped with a fixed, manually actuated fire extinguishing system with sucha layout as to cover the compartments. It shall be possible to actuate the extinguisher both from within thecompartments and from outside.

4.1.3 The extinguishing agent for the inner area shall be rechargeable without depressurising, and provisionsshall be made for possible discharge of less than the total supply of extinguishing agent

4.1.4 The extinguishing agent shall be water, unless an approved alternative exists.

4.1.5 Fixed water-mist systems for inner area shall have minimum capacity of 2 shots of 2 min. durationwith the required application rate. Response time upon activation shall follow NFPA99, maximum 3 sec.

5 Miscellaneous equipment

5.1 Portable fire extinguishers

5.1.1 Portable fire extinguishers of approved types and designs should be distributed throughout the spacecontaining the diving system. One of the portable fire-extinguishers should be stowed near the entrance tothat space.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.4.)

5.1.2 Portable fire extinguishers shall be of approved type and comply with FSS code Ch.4. For inner areahyperbaric extinguishers shall be of approved type, containing non-toxic medium and certified for themaximum depth rating of the chamber in which they are placed.

5.1.3 Spare charges or extinguishers shall be provided on-board, 100% for the first 10, and 50% forremaining extinguishers.

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SECTION 6 LAUNCH AND RECOVERY SYSTEMS (LARS)

1 Introduction

1.1 ObjectivesThe objectives of this section are to specify additional requirements for lifting appliances serving surfacediving systems. General requirements for lifting appliances are given in DNVGL-ST-0378 Sec.12 standard foroffshore lifting appliances, incorporating specific requirements for lifting of personnel.

1.2 Scope

1.2.1 Key issues are identified through requirements for alternative recovery of divers.

1.2.2 Limitations are given in the rating of the launch and recovery systems with respect to a given,specified, sea-state.

1.3 Application

1.3.1 These requirements apply to all surface diving systems.

1.3.2 This section applies to all launch and recovery systems. However, requirements for launch andrecovery of diver’s baskets may be more lenient with respect to emergency recovery, if it is possible for thesurface supplied divers to ascend independent of the diver’s basket.

1.3.3 This section has impact on the requirements for strength with respect to deck loading on the supportvessel and to the services from the support vessel.

1.4 ReferencesFor quantitative design parameters and functional requirements, see relevant standards and guidelines,including DNVGL-ST-0378 Standard for offshore lifting appliances.See:

a) App.B or equivalentb) DNVGL-RU-SHIP Pt.5 Ch.10c) ILO Convention No. 152.

1.5 DocumentationLaunch and recovery systems shall be documented as a lifting appliance in accordance with DNVGL-ST-0378standard for offshore lifting appliances. In addition, plans and supplementary documentation shall be madeavailable as follows:

a) Plans showing the arrangement of the launch and recovery system with specifications of loads, anddimensions of strength members.

b) Plans showing the function of the systems, and giving particulars of the systems. The plans shall showa schematic arrangement of the hydraulic or pneumatic piping systems and specification of controls andpower supply.

c) Calculation of the design load according to [3].d) Calculation of necessary design load for umbilical and guide ropes.

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e) Plans and specification of structural parts, ropes, sockets, blocks, sheaves, winches, and emergencyascent arrangement for the basket or wet-bell.

f) Specifications of materials and welds, and extent of non-destructive testing.g) Specifications of wire ropes and their end connections.h) Specification of safety devices (limit switches, automatic stop of operating handle, automatic locking of

winch in case of power failure, etc.).i) Plans and specifications for systems used for emergency ascent of the divers and retrieval of the basket

or wet-bell.j) Information on specification of working weight, displacement and stability of the basket or wet-bell, with

all hydrostatic properties accounted for.


1.6.1 Basket/wet-bell

a) The working weight shall be ascertained.b) The stability in normal and emergency modes shall be tested.

1.6.2 Launch and recovery systems shall be subjected to tests for structural strength and for function andpower.

1.6.3 A static load test to a load equal to the design load shall be carried out.

1.6.4 Functional and power testing of normal and emergency systems shall be carried out with a functionaltest load of 1.25 times the working weight in the most unfavourable position. It shall be demonstrated thatthe systems are capable of carrying out all motions in a safe and smooth manner.

1.6.5 Monitoring of functional parameters during the tests, e.g. pressure peaks in hydraulic systems may berequired.


1.7.1 During the sea trials the normal launch and recovery system shall be tested with the working weight ofthe basket or wet-bell to the maximum depth.

1.7.2 A recovery test of the basket or wet-bell shall be carried out simulating emergency operationsconditions.

1.8 Marking and signposts

1.8.1 The launch and recovery system shall, in an easily visible place, be fitted with a nameplate giving thefollowing particulars:

a) identification numberb) static test loadc) functional test loadd) working weighte) surveyor's mark and identification.

1.8.2 The above loads shall be specified for each subsystem involved.

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1.9 MaterialsMaterials shall be compliant with the requirements given in DNVGL-ST-0378 standard for offshore liftingappliances.

2 Design principles

2.1 General

2.1.1 Where the following IMO requirements refer to bell they shall also apply to divers’ baskets in thecontext of this standard.

2.1.2 A diving system should be equipped with a main handling system to ensure safe transportation of thediving bell between the work location and the surface compression chamber.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.1.)

2.1.3 Connection of the main lift wire to basket (or wet bell) shall have two retaining means for theremovable pin.

2.1.4 For diving operations where there are no hull obstructions near the diving site, and the freeboard isless than 2 metres, one of the following options shall be utilised:

a) wet bell or diving basket(s) including equipment for the deployment of a surface standby diverb) ladder which extends at least 2 metres below the surface in calm water. The ladder shall have sufficient

holds under and above water and on deck level to allow the diver to step easily onto the deck. Inaddition a dedicated arrangement e.g. a crane, A-frame or davit, certified for lifting of personnel, withsufficient reach shall be present to recover an incapacitated diver from the water by a safety harnessonto the deck.

2.1.5 For diving operations where there are obstructions at the diving site, and/or a freeboard of more than2 metres, one of the following options shall be utilised:

a) wet bell including equipment for the deployment of a surface standby diverb) two diving baskets, one for the diver(s) and one for the standby diver.

2.2 Divers basket and wet-bell (when installed)

2.2.1 A diving bell should:.1 be provided with adequate protection against mechanical damage during handling operation.2 be equipped with one extra lifting point designed to take the entire dry weight of the bell including ballastand equipment as well as the weight of the divers staying on in the bell..3 be equipped with means whereby each diver using the bell is able to enter and leave it safely as well aswith means for taking an unconscious diver up into a dry bell..4 (Omitted text not applicable for surface diving).(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.1.)

Guidance note:

The above IMO requirements for bells shall also apply to divers’ baskets in this case.

Note that the design and location of the extra lifting fastening needs to be considered in view of the need to bring a basket or wet-bell close to the surface decompression chamber.


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2.2.2 Internally there shall be an attachment for lifting of divers into the wet-bell or basket, if assistedrecovery is required in the particular design.

2.2.3 Each diving bell should have view ports that as far as practicable allow an occupant to observe diversoutside the bell.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.4.)The canopy of wet bells, if employed, shall be provided with windows that as far as practicable allow theoccupants to observe diving and lifting operations outside the wet-bell.

2.3 Function

2.3.1 The handling system should enable smooth and easily controllable handling of the diving bell.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.3.)The normal launch and recovery system shall be designed for a safe, smooth and easily controllabletransportation of the divers in the design sea-state.

2.3.2 The lowering of diving bells under normal conditions should not be controlled by brakes, but by thedrive system of the winches.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.4.)

2.3.3 If the energy supply to the handling system fails, brakes should be engaged automatically.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.5.)Manoeuvring systems shall be arranged for automatic stop when the operating handle is not operated (deadman’s handle).

2.3.4 Hoisting systems shall be fitted with a mechanical brake, which shall be engaged automatically whenthe hoisting motor stops. In the event of failure of the automatic brake a secondary means shall be providedto prevent the load from falling. This may be manual in operation and should be simple in design.

2.3.5 The launch and recovery system shall be designed so that the systems are locked in place if the energysupply fails or is switched off.

2.3.6 If the hoisting rope can enter the drum with an angle exceeding 2° from the right angle to the drumaxis (the fleet angle), a spooling arrangement shall be fitted. The rope launch and recovery system shall notpermit ropes to squeeze in between, or introduce permanent deformation to ropes in underlying layers on thedrum.

2.3.7 The hoisting system shall be equipped with a line-out device showing the amount of wire that isspooled off the drum and a device which stops the basket or wet-bell at its lowermost and uppermostpositions.

Guidance note:

Line-out monitoring is also needed when diving in certain adverse conditions, such as zero visibility. In such conditions it will benecessary to monitor line-out in order to safely carry out surface diving operations. When the diver is out of the stage, it should bepossible to match the diver’s depth with the depth of the stage.


2.3.8 Travelling cranes and trolleys shall be equipped with mechanical stops at their end positions. Thesystem shall be equipped with limit switches preventing the launch and recovery of the wet-bell or basket

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outside of the launch and recovery area. A-frames shall be arranged with stops to prevent luffing-out beyondthe maximum design angle.

2.3.9 Precautions shall be taken to avoid exceeding the design load in any part of the launch and recoverysystem including hoisting ropes and umbilical due to:

a) large capacity of the power unitb) motions of the supporting vessel when the basket/wet-bell or weights are caught or held by suction to

the sea floorc) failure on umbilical winch during launching of wet-bell.

2.3.10 Structural members of the launch and recovery system might be subjected to forces imposed byseparate units of a power system (e.g. A-frame tilted by hydraulic actuator on each leg.). The structuralmembers are therefore either to be strong enough to sustain the resulting forces when one of the powerunits fails, or the power units shall be synchronised and an automatic alarm and stop system shall beactivated when the synchronising is out of set limits.

2.3.11 Hydraulic power units shall be dedicated to the lifting appliance and not shared with other consumers,such as hydraulic driven tools.

2.3.12 Where direct visual monitoring of the winch drums from the winch control station is not practical, TVmonitoring shall be fitted.

2.3.13 Primary and emergency lighting in all critical launch and recovery areas shall be provided.

2.4 Recovery

2.4.1 In the event of single component failure of the main handling system, an alternative means shouldbe provided whereby the bell can be returned to the surface compression chamber. In addition, provisionsshould be made for emergency retrieval of the bell if the main and alternative means fail. (-omitted, non-applicable text-).(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.6.)There shall be at least one normal system (primary) and two (secondary and tertiary) mutually independentemergency means for recovery of the divers with return to the chambers. The alternative means shallcomply with the same requirements for load strength as the main system if the basket/wet-bell is part of therecovery.

2.4.2 The two emergency means shall be arranged as follows:

a) One emergency system (secondary) may be made for recovery by aid of the normal hoisting or guiderope(s). This system shall be independently powered from the normal system, and shall incorporate alltransportation necessary to transport the divers to the surface chamber.

b) One system (considered secondary) shall also provide an arrangement for stopping the basket or wet-bell from falling or descending, in the event of failure in the primary lifting wire.

2.4.3 Another emergency system, (tertiary), may be that the diving system is equipped with a separatelaunch and recovery system and a second basket or wet-bell. Provisions shall be available for recovery of thedivers to the chambers.Alternatively this other emergency system (tertiary) may consist of an arrangement that permits thedivers free ascend and shall incorporate all means necessary to transport the divers to the chamber. Whereappropriate, the emergency recovery may incorporate a ladder if the freeboard and distance to the chamberallows for this.

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2.4.4 The time taken to bring the diver(s) from 10 msw in the water until 10 msw equivalent in the chambershould not exceed 5 minutes in any of the three modes of recovery.

2.4.5 Guide wire equipment may, in addition to ensuring controlled movements of the basket or wet-bell inthe water, function as a secondary means of recovery.

2.5 Power

2.5.1 The hoisting power system shall be designed and tested to lift and manoeuvre a load of 1.25 times theworking weight of the basket or wet-bell.

Guidance note:

This requirement is to ensure there is enough power to handle the basket or wet-bell under normal wave conditions.


2.5.2 Handling systems and mating devices should enable easy and firm connection or disconnection ofa diving bell (-omitted, non-applicable text-), even under conditions where the support ship or floatingstructure is rolling, pitching or listing to predetermined degrees.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.7.)

2.5.3 The power of horizontal transportation systems shall be designed and tested for safe launch andrecovery at list and trim as specified in [3.1.4] and Sec.1 [5.2].

2.5.4 The strength of the mechanical brake for the hoisting system shall be based on holding of the designload. After the static test, however, the brake may be adjusted to the working weight of the basket or wet-bell plus 40%.

2.6 Umbilical

2.6.1 The length of the umbilicals, shall, as a minimum, allow an excursion of the basket or wet-bell to:

a) dmax plus 5%, orb) actual bottom depth plus 5%.

2.6.2 The termination points, where the umbilicals enter connectors and/or penetrators, shall not besubjected to significant loads or flexing.

2.6.3 The ultimate tensile strength of the umbilicals shall not be less than twice the maximum load expectedduring normal and emergency operations.

3 Strength

3.1 Design loads

3.1.1 The handling system should be designed with adequate safety factors considering the environmentaland operating conditions, including the dynamic loads which are encountered while handling the diving bellthrough the air-water interface.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.2.)See DNVGL-RU-SHIP Pt.3 Ch.1 Sec.3 (principles) and Sec.4.

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3.1.2 The minimum design load shall be taken as 2.0 times the working weight of the basket or wet-bellin air. For exposed launching, typically over the side or stern of vessels, the design load shall be estimatedas the largest most probable, resultant load over 24 hours in the operational design sea-state due to thefollowing:

a) working weight of basket or wet-bell and structural members of the launch and recovery systemb) dynamical amplification due to list, trim and motion of the vesselc) roll angles up to +/- 22.5 degreesd) operation and response of the launch and recovery systeme) hydrodynamic forcesf) jerks in the hoisting ropes and impact on the system.

3.1.3 The working weight of the basket or wet-bell shall be taken as the maximum weight of the fullyequipped basket or wet-bell, including each fully equipped diver of 200 kg. The load from this weight appliesto:

a) launch and recovery in air, andb) launch and recovery submerged, combining the maximum negative buoyancy of the wire rope, umbilical

and basket or wet-bell at maximum operating depth.

3.1.4 In locked positions on a vessel, the launch and recovery system shall have a structural strengthat least sufficient for the environmental conditions described in Sec.2. In addition to the motions andaccelerations in the operational design sea-state, the minimum inclinations given in Table 1 shall be takeninto account:

Table 1 Permanent inclinations

Vessel type Permanent list Permanent trim

Ship 5° 2°

Semi-submersible 3° 3°

3.1.5 Dynamic loads due to start, stop, or a slack wire rope followed by a jerk, and hydrodynamic loads shallbe estimated. Approximate estimates of expected dynamic loads during launch and recovery of diving basketor wet-bell and any connected cursor from a vessel which is stationary and heading in the main direction ofincoming waves in the design sea-state are given in App.B .

Guidance note:

In the case of transferable systems, there will be a wide variety of potential support vessels and installation options. It stands toreason that these diving systems are delivered with a set design load and owners need to apply the App.B calculations to set theparameters for operating capability so that this may be entered into a certificate appendix for the particular installation. In practicethe allowable operational loads may be regulated by load monitoring, as is done on modern diving systems. The App.A tool forestimating design loads, entered in a simple spread sheet, may be used to estimate sea states where the design load is given as aset value. The ship related variables can be altered when the estimation is carried out for a new installation on a different location.


3.2 Dimensions

3.2.1 The minimum safety factor for steel wire ropes shall be 4 compared to design load defined in [3.1].Minimum safety factor for synthetic fibre wire ropes shall be 5 compared to design load defined in [3.1].

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Guidance note:

Note that a SF of 4 times the minimum design load of 2.0 gives a SF of 8.0.


3.2.2 Blocks, sheaves, shackles etc. shall comply with recognised national codes. Drums and pulleydiameters shall correspond to the type of rope. For steel wire ropes this diameter shall not be taken less thanspecified by the rope manufacturer, and normally not less than 18 times the rope diameter. In the case ofcross hauling, such equipment shall fulfil the same requirements for strength as the rest of the launch andrecovery system.

3.2.3 Structural members shall be fabricated from certified materials and shall be designed with safetyagainst:

a) excessive yieldingb) bucklingc) fatigue fracture, andd) shall be in accordance with technical requirements in DNVGL-ST-0378 or equivalent accepted standards.

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SECTION 7 INSTRUMENTATION AND COMMUNICATION

1 Introduction

1.1 ObjectiveThe objectives of this section are to emphasise the special needs associated with the design and manufactureof diving systems. General requirements for instrumentation and communication systems and componentsare given in DNVGL-RU-SHIP Pt.4 Ch.9.

1.2 Scope

1.2.1 Recognised production standards include those provided by the International Electro TechnicalCommission (IEC).


1.3 Application

1.3.1 These requirements apply to all surface diving systems.

1.3.2 This section bears impact on Ch.2 Sec.1 (location of surface diving system in hazardous zones), Sec.3,Sec.5, Sec.6 and Sec.8.

1.4 ReferencesThe following codes and standards are applicable:

— DNVGL-OS-D202 Automation, safety and telecommunication systems— DNVGL-OS-D201 Ch.2 Sec.2 [6.3] electrical power requirements for control and monitoring systems— relevant IEC equipment construction and design standards.

1.5 Documentation

1.5.1 The following document requirements assume a non-complex system. For complex instrumentationand/or communication systems, scope shall be agreed on a case by case basis at the start of the project.

1.5.2 For instrumentation and communication systems the following shall be documented:

a) Complete key diagrams, of control and alarm circuits for all motors or other consumers.b) Plans showing arrangements of batteries with information about their make, type and capacity.c) Plans showing arrangement and single line diagrams of the communication system.d) Complete list of components and documentation on any tests carried out on all equipment to be

permanently installed within the chamber and the wet-bell.

1.6 Survey and testing requirements during and after manufactureThe correct calibration of all essential instrumentation (compartment pressure gauges, gas analysisinstruments etc.) shall be checked.

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1.7.1 Communication shall be tested after assembly, for proper function.

1.7.2 Control and monitoring system shall be tested according to an approved test procedure.

1.8 Survey and testing requirements during and after installationDuring the sea trials the normal launch and recovery system will be tested to the maximum depth. Forsurface diving systems employing a wet-bell the communication system shall be tested.

1.9 Markings and signboardsMarkings and signboards shall be posted according to the relevant requirements in DNVGL-OS-D201 Ch.2Sec.3 [5] and DNVGL-OS-D202 Ch.2 Sec.4 [1.5].

1.10 MaterialsEquipment, including enclosures, shall meet the environmental requirements given in DNVGL-RU-SHIP Pt.4Ch.9 Sec.5.

2 Instrumentation

2.1 General

2.1.1 A diving system should include the control equipment necessary for safe performance of divingoperations.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.7.)

2.1.2 In general, instrumentation shall comply with the relevant requirements in DNVGL-OS-D202.

2.2 Power supply to control and monitoring systems

2.2.1 Power supply requirements for control and monitoring systems shall comply with the principles given inDNVGL-OS-D202.

2.2.2 Where instrumentation requires power supplies, this shall be designed on the basis of the systemphilosophy and redundancy philosophy as applicable. Requirements for essential, emergency and normalservices are given in Sec.1 [4].

2.3 Monitoring and inspection during operation

2.3.1 Parameters that could jeopardise the safety of the divers, and or violate the integrity of a divingsystem, shall be monitored and evaluated with a frequency that enables remedial actions to be carried outbefore personal harm is done or the system is damaged.

Guidance note:

As a minimum the monitoring and inspection frequency should be such that the diving system, and consequently the surface divingoperation, shall not be endangered due to any realistic degradation or deterioration that may occur between two consecutiveinspection intervals.


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2.3.2 Instrumentation may be required when visual inspection or simple measurements are not consideredpractical or reliable, and available design methods and previous experience are not sufficient for a reliableprediction of the performance of the system.

2.3.3 The various pressures in a diving system shall not exceed the design pressures of the componentsduring normal steady-state operation.

2.4 Pressure control system

2.4.1 The set pressures of the pressure regulating system shall be such that the local operational pressuresare not exceeded at any point in the diving system. Due account shall be given to the tolerances of thepressure regulating system and the associated instrumentation.

Guidance note:

A pressure control system is used to prevent the internal pressures at any point in the diving system rising to excessive levels, orfalling below prescribed levels. The pressure control system comprises the pressure regulating systems, pressure safety systemsand associated instrumentation and alarm systems. The purpose of the pressure regulating system is to maintain the operatingpressures within acceptable limits during normal operation. The purpose of the pressure safety systems is to protect the systemsduring abnormal conditions, e.g. in the event of failure of the pressure regulating systems.


2.4.2 The pressure safety systems shall operate automatically in accordance with the fail safe principles andwith set pressures such that there is a low probability for:

a) the internal pressure at any point in the diving system to exceed the design pressure (maximumoperating pressure), and for

b) the unintentional loss of pressure at any point in the diving system to fall below set values.

2.4.3 The diving system may be divided into sections with different design pressures provided the pressurecontrol system ensures that for each section, the local operational pressure cannot be exceeded duringnormal operations and that the design pressure cannot be exceeded during abnormal operation.The pressure control shall also ensure that unwanted loss of pressure in one section does not occur as aresult of an abnormal condition in another section.

2.5 Control stands

2.5.1 With reference to requirements in Sec.4 and DNVGL-OS-D202 Ch.2 Sec.5, the design of control roomsshall consider ergonomics such as communication and a systematic arrangement of equipment, accordingto a documented traffic flow chart. Further, it shall be ensured that noise or other disturbance when workingdoes not occur. Control stands for diving operations shall therefore be separated from the control stationsassociated with the other operations on board.

2.5.2 The diving system should be so arranged as to ensure that centralized control of the safe operation ofthe system can be maintained under all weather conditions.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.11.1.)

2.5.3 Indication and operation of all vital life support conditions to and from the divers, the chamber(s)and the wet-bell(s) shall be arranged at a single control stand. The control stand shall be equipped for easyoperation and control of the diving system. There shall be schematic indication of gas flow lines.

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2.5.4 A surface compression chamber should be equipped with such valves, gauges and other fittings asare necessary to control and indicate the internal pressure and safe environment of each compartment fromoutside the chamber at a centralized position.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.2.)

Table 1 As a minimum, facilities should be provided at the central control position to monitor thevalues of the following parameters for each occupied compartment:

CompartmentsParameters

Surface compression chamber Diving bell

CO2 partial pressure Yes Yes

Humidity Yes

Oxygen partial pressure *1 Yes Yes

Pressure or depth *1 Yes Yes *2

Temperature *1 Yes

*1/ These parameters should be indicated continuously.

*2/ Pressure or depth (omitted non-applicable text) outside bell should be indicated.


2.5.5 The control stands shall also have indicators showing continuously:

— the pressure in the surface mounted gas containers connected— the pressure after all pressure reducers— the pressure in each chamber compartment— the pressure (depth) at each divers location— the pressure at the wet-bell (if employed).

2.5.6 Pressure indicators on the control stand for the divers, the wet-bell and chamber compartments shallbe arranged for a possible comparison between each other or with a permanently installed master indicator.If cross-connections are incorporated, these shall be arranged in such a way as to give the operators anindication when cross-connection is being conducted.

2.5.7 Instrumentation for pressure measuring for the divers, the wet-bell and chamber compartmentsshall have an accuracy of +/-0.3% of full scale. In addition, to facilitate accurate decompression, pressureindicators for the chambers shall facilitate depth measurements with an accuracy of +/-0.25 msw. in thedepth range from 30 msw. to 0. The accuracy of other instruments for pressure measuring shall be +/-1% offull scale.

2.5.8 The control stands shall also have a system for continuous indication of:

a) oxygen content in each compartment individuallyb) oxygen content in the supply to the:

i) umbilicalsii) compartmentsiii) masks in compartments.

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2.5.9 The monitoring systems shall be fitted with audible and visual high and low level alarm.

2.5.10 A list of the essential gauges in the system shall be posted at the control stand.

2.5.11 Permanent provisions for calibration of, and comparison and back-up between, oxygen analysinginstruments shall be arranged on the control stand.

2.5.12 There shall be an audio-visual gas flow indicator in the oxygen supply to the chambers, whenapplicable.

2.5.13 The control stands shall have a system for regular indication of carbon dioxide content in eachcompartment individually.

2.5.14 There shall be systems for indication of temperature and humidity in the inner area displayed at thecontrol stand.

2.5.15 Alarms for abnormal conditions are required at the control stand, if automatic environmental controlsystems are arranged for regulation of gas composition, pressure and temperature in the inner area.

2.6 Pressure indicators in wet-bell and chambers

2.6.1 Valves, gauges and other fittings should be provided outside the bell as necessary to control andindicate the pressure and safe environment within the diving bell.(omitted text)(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.3.)

2.6.2 A wet-bell shall contain local equipment to monitor important parameters in all situations, such asdepth, pressure of gas supply from surface, pressure of on-board emergency gas supply

2.6.3 The chamber compartments shall be fitted with indicators visible to the divers inside, showing internalpressure.

2.6.4 Means shall be provided for isolating all pressure indicators without interrupting vital functions in thegas distribution system. If isolation is incorporated, these shall be arranged in such a way as to give theoperators an indication when isolation is being conducted.

2.7 Oxygen and carbon dioxide analysing systems in wet-bell and chambers

2.7.1 Provision should be made within the bell for an independent means of monitoring oxygen and carbondioxide levels.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.11.3.)In the case of diving in a wet-bell, this is only required when risk evaluation according to given locations andoperations reveal a need for monitoring these parameters locally in the wet-bell.

2.7.2 Oxygen analysing systems shall have an accuracy of at least +/-0.015 bar partial pressure oxygen.

2.7.3 The chamber compartments shall have independent oxygen analysers inside.

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2.7.4 Carbon dioxide analysing systems shall have an accuracy of +/-0.001 bar partial pressure.

2.7.5 Carbon dioxide gas mixture for calibration shall be available.

2.8 Other gases

2.8.1 Where breathing gas is supplied directly from running compressors, a means of analysing the air forCarbon Monoxide shall be provided for continuous monitoring - incorporating audio/visual alarm.

2.8.2 The instrumentation for systems intended for other gases than air and oxygen mixes shall beconsidered in each case, including hydrogen sulphide.

2.8.3 Diving shall not take place if CO and/or H2S are present, and there shall be a system for shutting downintakes of air into the diving system in cases where these gases may be present.

Guidance note:

Operations in connection with exploration of oil may require instrumentation for the analysis of hydrocarbon gases and H2S.


2.8.4 Calibration gases shall be available for each relevant gas mix.

2.9 Automatic environmental control systems (if employed)

2.9.1 The following requirements apply when systems for automatic regulation of gas composition, pressureand temperature in the inner area are installed.

2.9.2 The design principles given in DNVGL-OS-D202, apply on a general basis.

2.9.3 The most probable failure in the systems shall result in the least critical of any possible new conditions(fail to safety).

2.9.4 Automatic control systems shall keep process variables within the limits specified during normalworking conditions and the alarm systems shall be activated when the limits are exceeded.

2.9.5 Alarm at the control stand is required for abnormal conditions. The alarm system is also to be activatedby failures in the alarm system circuitry. The alarm system shall be independent of the automatic controlsystem so that failure in one of the systems cannot inhibit operation of the other system.

2.9.6 A manual back-up system for the automatic control system is required.

3 Communication

3.1 GeneralCommunications systems shall comply with the relevant requirements given in DNVGL-RU-SHIP Pt.5 Ch.10.

3.2 Visual observation of diversVisual observation of divers in each compartment shall be possible.

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3.3 Voice communication systems

3.3.1 Voice communication should be hard-wired, especially when critical operations are coordinated.

3.3.2 The communication system should be arranged for direct two-way communication between the controlstand and:

— diver in water— diving bell— each compartment of the chambers— diving system handling positions— dynamic positioning room— bridge, ship's command centre or drilling floor.


3.3.3 Communication systems shall be arranged for direct voice communication between the control standand other control stations as needed. If a crane is employed during diving operations, there shall be directcommunications with the crane operator.

3.3.4 Alternative means of communication with divers in the surface compression chamber and diving bellshould be available in emergency.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.12.2.)

3.3.5 The control stand for the divers in the water shall be provided with equipment for audio-recording of allcommunications with the divers.

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SECTION 8 EVACUATION SYSTEMS

1 Introduction

1.1 ObjectivesThe objective of this section is to inform on requirements for evacuation systems as regulated by themaritime administrations and/or shelf state authorities.

1.2 ScopeThe scope of work is according to instructions from the maritime administration.

1.3 ApplicationThis section applies to all surface diving systems where SOLAS requirements may be applied if practicablypossible. These requirements may also be applicable as flag state, or shelf state, requirements. Theauthorities are then contacted as part of the ISM audits or the safety case.

1.4 Referencesa) SOLASb) IMO guidelines for hyperbaric evacuationc) DNVGL-RP-E403 hyperbaric evacuation systems.

1.5 DocumentationContingency plans with details of responsibilities, equipment, systems and escape routes.

1.6 Survey and testing requirementsSee DNVGL-RP-E403.

1.7 Marking and signboardsSee DNVGL-RP-E403.

1.8 MaterialsSee DNVGL-RP-E403.

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CHAPTER 3 SATURATION DIVING SYSTEMS

SECTION 1 DESIGN PHILOSOPHY AND PREMISES

1 IntroductionThis section presents the safety philosophy applied in this chapter. It also identifies and provides a basis fordefinition of relevant system design characteristics. Further, key issues required for design, construction,operation and re-qualification of diving systems are identified. In addition, it list minimum requirementsfor documentation for design, manufacture, installation and some operational aspects. Conclusively somegeneral guidance is given, such as safety philosophy and design premises.

2 Safety philosophy

2.1 GeneralThe integrity of a diving system constructed to this standard is ensured through a safety philosophyintegrating different parts as illustrated in Figure 1.

Guidance note:

Safety of the diving system may be ensured by use of a safety class methodology. The diving system is then classified into oneor more safety classes based on failure consequences, normally given by the particular operation. For each safety class, a set ofpartial safety factors is assigned to each limit state.


2.2 Safety objectiveAn overall safety objective shall be established, planned and implemented, covering all phases fromconceptual development until demobilisation and scrapping.

Guidance note:

All companies have some sort of policy regarding human aspects, environment and financial issues. These are typically on anoverall level, but more detailed objectives and requirements in specific areas may follow them. These policies should be used as abasis for defining the safety objective for a specific diving system. Typical statements can be:

— There shall be no serious accidents or loss of life during the construction period.

Statements such as the above may have implications for all or individual phases only. They are typically more relevant for the workexecution (i.e. how the contractor executes his job) and specific design solutions. Having defined the safety objective, it can bea point of discussion as to whether this is being accomplished in the actual project. It is therefore recommended that the overallsafety objective be followed up by more specific, measurable requirements.

If no policy is available, or if it is difficult to define the safety objective, one could also start with a risk assessment. The riskassessment could identify all hazards and their consequences, and then enable back-extrapolation to define acceptance criteria andareas that need to be followed up more closely.


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Figure 1 Safety philosophy structure

2.3 Systematic review

2.3.1 As far as practical, all work associated with the design, construction and operation of the diving systemshall be such as to ensure that no single failure shall lead to life-threatening situations for any person, or tounacceptable damage to the facilities or the environment.

2.3.2 A systematic review or analysis shall be carried out at all phases in order to identify and evaluate theconsequences of single failures and series of failures in the diving system, such that necessary remedialmeasures can be taken. The extent of the review or analysis shall reflect the criticality of the diving system,the criticality of a planned operation and previous experience with similar systems or operations.

Guidance note:

A methodology for such a systematic review is quantitative risk analysis (QRA). This may provide an estimation of the overall riskto human health and safety, environment and assets and comprises:

— hazard identification

— assessment of probabilities of failure events

— accident developments

— consequence and risk assessment.

It should be noted that legislation in some countries requires risk analysis to be performed, at least at an overall level to identifycritical scenarios that might jeopardise safety and reliability. Other methodologies for identification of potential hazards are failuremode and effect analysis (FMEA) and hazard and operability studies (HAZOP).


2.3.3 Special attention shall be given to the risk of bell handling, fire and evacuation.

2.4 Quality assurance

2.4.1 The safety format within this standard requires that gross errors (human errors) shall be controlled by:

a) requirements for organisation of the workb) competence of persons performing the work

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c) verification of the designd) quality assurance during all relevant phases.

2.4.2 For the purpose of this standard, it is assumed that the owner of a diving system has established aquality objective. The owner shall, in both internal and external quality related aspects, seek to achievethe quality level of products and services intended in the quality objective. Further, the owner shall provideassurance that intended quality is being, or shall be, achieved.

2.4.3 A quality system shall be applied to assist compliance with the requirements of this standard.Guidance note:

ISO 9000 gives guidance on the selection and use of quality systems, and ISO 10013 gives guidance on developing qualitymanuals.


3 General premises

3.1 Concept development

3.1.1 Data and description of system development and general arrangement of the diving system shall beestablished.

3.1.2 The data and description shall include the following, as applicable:

a) safety objectiveb) locations, foundations and interface conditionsc) diving system description with general arrangement and system limitsd) functional requirements including system development restrictions, e.g. significant wave height,

hazardous areas, fire protectione) installation, repair and replacement of system elements and fittingsf) project plans and schedule, including planned period for installationg) design life including specification for start of design life, e.g. final commissioning, installationh) data of contained liquids and gasesi) capacity and sizing dataj) geometrical restrictions such as specifications of diameter, requirement for fittings, valves, flanges and

the use of flexible hosesk) second and third party activities.

3.2 Execution planAn execution plan shall be developed, including the following topics:

a) general information, including project organisation, scope of work, interfaces, project developmentphases and production phases

b) contacts with purchaser, authorities, third party, engineering, verification and construction contractorsc) legal aspects, e.g. insurance, contracts, statutory requirements.

3.3 Plan for manufacture, installation and operation

3.3.1 The design and planning for a diving system shall cover all development phases including manufacture,installation and operation.

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3.3.2 ManufactureFor a documentation overview, see [8] documentation.

3.3.3 InstallationDetailed plans, drawings and procedures shall be prepared for all installation activities. The following shall asa minimum be covered:

a) diving system location overview (planned or existing)b) other vessel (or fixed location) functions and operationsc) list of diving system installation activitiesd) alignment rectificatione) installation of foundation structuresf) installation of interconnecting servicesg) installation of protective devicesh) hook-up to support systemsi) as-built surveyj) final testing and preparation for operation.

3.3.4 OperationPlans for diving system operation, inspection, maintenance and repair shall be prepared prior to start ofoperation.All operational aspects shall be considered when selecting the diving system concept.The diving system operational planning shall as a minimum cover:

a) organisation and managementb) start-up and shut-down (pre and post dive)c) operational limitationsd) emergency operationse) maintenancef) corrosion control, inspection and monitoringg) general inspectionh) special activities.

3.3.5 DemobilisationDemobilisation shall be planned and prepared.Evaluation shall include the following aspects:

a) safety aspects, during and after demobilisationb) environmental aspects, e.g. pollutionc) impact on other structuresd) possible reuse of equipment at a later stage (re-qualification and certification).

4 System design principles

4.1 System integrity

4.1.1 Diving systems shall be designed, constructed and operated in such a manner that they:

a) fulfil the specified operational requirementsb) fulfil the defined safety objective and have the required support capabilities during planned operational

conditions

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c) have sufficient safety margin against accidental loads or unplanned operational conditions.

4.1.2 The possibility of changes in the operating conditions and criteria during the lifetime of the system.

4.1.3 Any re-qualification deemed necessary due to changes in the design conditions shall take place inaccordance with provisions set out in each section of the standard.

4.2 Monitoring and inspection during operation

4.2.1 Parameters that could jeopardise the safety of the divers, and or violate the integrity of a divingsystem, shall be monitored and evaluated with a frequency that enables remedial actions to be carried outbefore personal harm is done or the system is damaged.

Guidance note:

As a minimum the monitoring and inspection frequency should be such that the diving system, and consequently the divingoperation, should not be endangered due to any realistic degradation or deterioration that may occur between two consecutiveinspection intervals.


4.2.2 Instrumentation may be required when visual inspection or simple measurements are not consideredpractical or reliable, and available design methods and previous experience are not sufficient for a reliableprediction of the performance of the system.

4.2.3 The various pressures in a diving system shall not exceed the design pressures of the componentsduring normal steady-state operation.

4.3 Pressure control system

4.3.1 A pressure control system is be used to prevent the internal pressures at any point in the divingsystem rising to excessive levels, or falling below prescribed levels. The pressure control system comprisesthe pressure regulating systems, pressure safety systems and associated instrumentation and alarmsystems.

4.3.2 The purpose of the pressure regulating system is to maintain the operating pressures within acceptablelimits during normal operation. The set pressures of the pressure regulating system shall be such that thelocal operational pressures are not exceeded at any point in the diving system. Due account shall be given tothe tolerances of the pressure regulating system and the associated instrumentation.

4.3.3 The purpose of the pressure safety systems is to protect the systems during abnormal conditions,e.g. in the event of failure of the pressure regulating systems. The pressure safety systems shall operateautomatically in accordance with the fail safe principles and with set pressures such that there is a lowprobability for:

a) The internal pressure at any point in the diving system to exceed the design pressure (maximumoperating pressure) (see Sec.3 [2.2]).

b) The unintentional loss of pressure at any point in the diving system to exceed set values (see Sec.3[5.3]).

4.3.4 The diving system may be divided into sections with different design pressures provided the pressurecontrol system ensures that; for each section, the local operational pressure cannot be exceeded duringnormal operations and that the design pressure cannot be exceeded during abnormal operation.

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The pressure control shall also ensure that unwanted loss of pressure in one section does not occur as aresult of an abnormal condition in another section.

5 Diving system arrangement and layout

5.1 General

5.1.1 The systems shall be so designed that the effect of a single failure cannot develop into hazardoussituations for the divers.

Guidance note:

Whereas this is a general requirement for the systems, it is recognised that certain components cannot fulfil this requirement inand of themselves. A typical example of this is the pressure vessel for human occupancy with acrylic windows.

In these cases the applicable standards will specify stringent safety factors. For other cases a formal safety assessment may berequired.


5.1.2 The diving system shall be so designed that the divers and assisting personnel are provided with safeand comfortable operating conditions. Ergonomic principles shall be applied in the design of working systems.(i.e. in accordance with ISO 6385.)

5.1.3 The diving system shall contain a minimum of two compartments. The smaller of the twocompartments shall be large enough for two persons. One of the compartments shall be a livingcompartment. For saturation diving systems, a minimum of two compartments shall be designed for keepingthe pressure independent of the pressure in the other compartment(s).

5.1.4 When the diving system is taken onboard and mobilised for use, equipment related to the divingsystem shall be permanently attached to the hull structure (e.g. by welding, screwed connection or similar).Fitting by means of lashing is not considered as permanent fitting.

5.2 Layout of the diving systemThe layout of the diving system on board shall ensure protection from accidental damage and accessibilityfor:

a) safe operationb) maintenancec) inspection.

6 Environmental conditions

6.1 General

6.1.1 Systems and components shall be designed for the environmental conditions expected at their installedlocation (on the vessel or otherwise) and their geographic site of operation.

6.1.2 All systems and components shall be able to operate satisfactorily and safe in accordance with theirspecifications at the environmental conditions stated in [7].

6.1.3 Additional requirements for various systems and components may, however, be given elsewhere in theStandard.

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6.1.4 The effects of environmental phenomena relevant for the particular location and operation in questionshall be taken into account.

6.1.5 Environmental phenomena that might impair proper functioning of the system or cause a reduction ofthe reliability and safety of the system shall be considered, (including fixed and land-based installations):

— temperature— wind, tide, waves, current— ice, earthquake, soil conditions— marine growth and fouling.

6.2 Collection of environmental dataThe environmental data shall be representative for the geographical areas in which diving systems may beoperated. Estimates based on data from relevant locations may be used.

Guidance note:

Environmental parameters may be described using characteristic values based on statistical data or long-term observations.

Statistical data may be utilised to describe environmental parameters of a random nature (e.g. wind, waves). The parametersshould be derived in a statistically valid manner using recognised methods.


6.3 Wind

6.3.1 Where appropriate, wind effects shall be considered in the design of handling systems, including thepossibility of wind induced vibrations of exposed free spans.

6.3.2 For spans adjacent to other structural parts, possible effects due to disturbance of the flow field shallbe considered when determining the wind actions. Such effects may cause an increased or reduced windspeed, or a dynamic excitation by vortices being shed from adjacent structural parts.

6.4 Tide

6.4.1 Tide effects shall be considered when this is a significant parameter, e.g. handling systems on shorebased installations.

6.4.2 The assumed maximum tide shall include both astronomic tide and storm surge. Minimum tideestimates should be based upon the astronomic tide and possible negative storm surge.

6.5 Waves

6.5.1 Maximum sea-state, defined by maximum significant wave height, shall be specified and used in thedesign calculations. Calculations may be done in accordance with specifications in App.B.

6.5.2 The wave data to be used in the design of handling systems are in principle the same as the wave dataused in the design of the structure supporting the system.

6.5.3 Direct and indirect wave effects shall be taken into consideration.

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6.5.4 When appropriate, consideration shall be given to wave refraction and shoaling, shielding, andreflecting effects.

6.5.5 Where the handling system is positioned adjacent to other structural parts, possible effects due todisturbance of the flow field should be considered when determining the wave actions. Such effects maycause an increased or reduced velocity, or dynamic excitation by vortices being shed from the adjacentstructural parts.

6.5.6 Where appropriate, consideration should be given to wave direction and short crested waveform.

6.6 Current

6.6.1 The effect of current shall be taken into consideration.

6.6.2 Current velocities shall include contributions from positioning systems, tidal current, wind-inducedcurrent, storm surge current, and other possible current phenomena. For near-shore fixed installations, long-shore current due to wave breaking shall be considered.

6.6.3 The variations in current velocity magnitude and direction as a function of water depth may need to beconsidered. For fixed installations, the current velocity distribution shall be the same as the one used in thedesign of the offshore structure supporting the system.

6.7 IceFor areas where ice may develop or drift, consideration shall be given to possible effects, including:

a) ice forces on the system (added loads may be due to increased diameters or surface area)b) impacts from drifting icec) icing problems during construction and installation.

6.8 Air and sea temperatures

6.8.1 Air and sea temperature statistics may be provided giving representative design values specified in theterms of delivery.

6.8.2 Monitoring of temperature may be required during construction, installation and commissioning phasesif the effect of temperature or temperature variations has a significant impact on the safety of the divingsystem.

6.8.3 The interactive effects of temperature and humidity shall be considered.

6.9 Marine growth

6.9.1 The effect of marine growth on diving systems shall be considered, taking into account both biologicaland other environmental phenomena relevant for the location.

6.9.2 The estimation of hydrodynamic loads shall be considered in the cases where marine growth mighthave an impact on the effective surface area or surface roughness.

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7 External and internal system condition

7.1 External operational conditions and outer area

7.1.1 Design inclinations shall be according to Table I.

Table 1 Design inclinations

Location Roll Permanentlist

Pitch Trim

Chambers and other surface installations:

on a ship+/-22.5° +/-15° +/-10° +/-5°

On a mobile offshore unit +/-15° +/-15°

Components in a bell +/-45° +/-22.5°

Guidance note:

For handling systems the operational design sea-state is given in Sec.7 [3.1].


7.1.2 Range of ambient temperature: -10°C to 55°C, unless otherwise specified. For greater temperatureranges, temperature protection shall be provided.

7.1.3 Humidity: 100%.

7.1.4 Atmosphere contaminated by salt (NaCl):up to 1 mg salt per 1 m3 of air, at all relevant temperatures and humidity conditions.

7.2 Submerged components

7.2.1 Range of ambient temperature: -2°C to 30°C.

7.2.2 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to maximum operatingdepth.

7.2.3 Salinity of ambient water: 35 parts per thousand.

7.2.4 The pressure equivalent to depth of seawater at 0°C with 3.5% salinity may be taken as 1.006 bar per10 msw (meter seawater), as a mean value between 0 and 200 m depth.For saltwater, the density may be taken to vary as follows:

— 0.05% increase for each 100 m of depth increase— 0.4% increase for an increase in salinity from 3.5% to 4.0%— 0.3% decrease for an increase in temperature from 10°C to 20°C.

7.2.5 For the selection and detailed design for external corrosion control, the conditions relating to theenvironment shall be defined.

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7.3 Internal conditions

7.3.1 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to dmax with pressurisationand depressurisation rates as specified in Sec.3 [3.1].

7.3.2 Range of ambient temperature: 5°C to 55°C, unless otherwise specified.

7.3.3 Relative humidity: up to 100%.

7.3.4 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at relevant temperatures andhumidity conditions.

7.3.5 A description of the internal conditions during storage, construction, installation, pressure testing andcommissioning shall be prepared. The duration of exposure to seawater or humid air, and the need for usingmeasures to control corrosion shall be considered.When choosing materials, paints etc. the potential for emission of hazardous compounds shall be considered.Statutory requirements apply for determination of exposure limits such as:

a) American Conference of Governmental Industrial Hygienists, documentation of the threshold limit valuesand biological exposure

b) European Commission Directive on occupational exposure limit valuesc) health and safety executive occupational exposure limits.

7.4 Internal operational conditionsIn order to assess the need for internal corrosion control, including corrosion allowance and provision forinspection and monitoring, the following conditions shall be defined:

a) maximum and average operating temperature and pressure profiles of the components, and expectedvariations during the design life

b) expected content of dissolved salts in fluids, residual oxygen and active chlorine in sea water)c) chemical additions and provisions for periodic cleaningd) provision for inspection of corrosion damage and expected capabilities of inspection tools (i.e. detection

limits and sizing capabilities for relevant forms of corrosion damage)e) the possibility of wear and tear, galvanic effects and effects in still water pools shall be considered.

8 Documentation

8.1 General

8.1.1 This section specifies the requirements for documentation during diving system design, manufacturing,fabrication, installation, commissioning and operation.

8.1.2 In accordance with quality system requirements, design output shall be documented and expressed interms that can be verified and validated against design input requirements.The supplier shall establish and maintain documented procedures to control all documents and data.This may in part be done in accordance with the DNV GL document requirements lists (DOCREQ).

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8.1.3 All documentation requirements shall be reflected in a document register. The documentation shallcover design, manufacturing, fabrication, installation and commissioning. As a minimum, the register shallreflect activities from the start of design to operation of the diving system.

8.1.4 The documentation shall be submitted to the relevant parties for acceptance, verification orinformation as agreed in ample time before start of fabrication.

8.1.5 Verified documentation shall be available at the work site before manufacturing commences.

8.2 Documentation of arrangement etc.a) plans showing general arrangement of the diving system, location and supporting arrangementb) plans showing the lay-out of control stand(s)c) proposed program for tests and trials of systems for normal operation and for emergency use.

8.2.1 List stating the following particulars for the diving system:

a) maximum operating depth dmax and maximum observation depth for the bellb) maximum operation time Topc) maximum number of divers in the belld) maximum number of divers in the chamber(s) and bell(s)e) maximum operational sea-statef) extract from the operation manual, stating the operational procedures, as basis for the design.

8.3 Documentation for systems in operation

8.3.1 In order to carry out periodical surveys, the minimum documentation shall include:

a) personnel responsible for the operation of diving systemb) history of diving system operation with reference to events which may have significance to design and

safetyc) a log of the total number of dives and hours of saturation in the periods between annual surveysd) records of new equipment installed and old equipment removede) installation condition data as necessary for understanding diving system design and configuration, e.g.

previous survey reports, as-built installation drawings and test reportsf) inspection and maintenance schedules and their records.

8.3.2 In case of mechanical damage or other abnormalities that might impair the safety, reliability, strengthand stability of the diving system, the following documentation shall, as a minimum, be prepared prior tostart-up of the diving system:

a) description of the damage to the diving system, its sub-systems or components with due reference tolocation, type, extent of damage and temporary measures, if any

b) plans and full particulars of repairs, modifications and replacements, including contingency measuresc) further documentation with respect to particular repair, modification and replacement, as agreed upon in

line with those for the manufacturing or installation phase.

8.4 Filing of documentation

8.4.1 Maintenance of complete files of all relevant documentation during the life of the diving system is theresponsibility of the owner.

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8.4.2 The engineering documentation shall be filed by the owner or by the engineering contractor for aminimum of 10 years.

8.4.3 Design basis and key data for the diving system shall be filed for the lifetime of the system. Thisincludes documentation from design to start-up and also documentation from possible major repair ormodification of the diving system.

8.4.4 Files to be kept from the operational and maintenance phases of the diving system shall, as aminimum, include final in-service inspection reports from start-up, periodical and special inspections,condition monitoring records, and final reports of maintenance and repair.

9 Inspection and testing

9.1 General

9.1.1 When a diving system is built according to this standard, an inspector or surveyor shall verify that:

a) the design and scantlings comply with the approved plans and the requirements in this standard andother specified recognized standards, codes, and national regulations

b) that the materials and components are certified according to this standard and the terms of deliveryc) that the work is carried out in accordance with the specified fabrication tolerances and required quality of

welds etc.d) that piping systems conducting gas in life support systems are cleaned in accordance with an approved

cleaning procedure conforming to requirements given in ASTM G93-03 standard practice for cleaningmethods and cleanliness levels for materials and equipment used in oxygen-enriched environments

e) that gas cylinders are clean and sealedf) that all required tests are carried out.

9.1.2 The inspection shall be carried out at the manufacturers, during the assembly and during installation.The extent and method of examination shall be agreed in the terms of delivery.

9.1.3 The tests to be carried out are stated in [9.2] and [9.3]. Additional tests may, however, be required.The testing after completed installation shall be in compliance with an approved program.

9.2 Testing at the manufacturers

9.2.1 Pressure tests

a) Welded pressure vessels and seamless steel gas containers for internal pressure shall be hydrostatictested to an internal pressure in accordance with the design code. Each compartment in chambers shallbe tested separately.

b) Bells and pressure vessels for external pressure shall, in addition to the internal pressure testing, behydrostatic tested to an external pressure in accordance with the design code.

c) Acrylic plastic windows shall be tested in accordance with ASME PVHO-1-2012 Sec.2.The applied hydrostatic test pressure shall be the greater of:

i) 1.3 times the design pressureii) the test pressure of the bell/chamber for which the window is intended, but shall not exceed 1.5

times the design pressure of the window.

d) Compressor components subjected to pressure shall be hydrostatic tested in accordance with the designcode.

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9.2.2 Compressors

a) Compressors shall be tested for the gas types and pressure.b) The tests shall incorporate measurements of humidity and possible contaminants in the gas delivered.

9.2.3 Closed circuit breathing system (CCBS)CCBS shall be tested according to an approved test program incorporating the following:

a) breathing resistance at workb) simulation of the most probable failures and recording of the resulting system responsesc) performance of the system with regard to gas composition, pressure and temperature as function of the

variablesd) The results of the tests shall be made available for approval.

9.2.4 Flexible hosesFlexible hoses shall be tested as specified in Sec.7.

9.2.5 UmbilicalsUmbilicals shall be tested as specified in Sec.7.

9.2.6 Electrical pressure vessel penetratorsElectrical penetrators shall be tested as specified in Sec.4.

9.2.7 Bell

a) the working weight and the buoyancy shall be ascertainedb) the stability in normal and emergency modes shall be testedc) a shallow water ballast release test shall be carried out if fittedd) emergency release systems for hoisting rope and umbilical shall be tested.

9.3 Testing after completed installation

9.3.1 Pressure testsPiping for the life support systems shall be pressure tested to 1.5 times the maximum working pressure.Hydraulic systems may, however, be tested to the smaller of 1.5 times the maximum working pressure, or 70bar in excess of the maximum working pressure.

9.3.2 Purity testsPiping systems intended to be used in breathing gas and oxygen systems shall be tested for purity inaccordance with requirements given in ASTM G93-03 standard practice for cleaning methods and cleanlinesslevels for materials and equipment used in oxygen-enriched environments.The tests shall comprise:

a) measurement of contamination of the cleaning agent used at the last stage of the cleaningb) tests for possible traces of cleaning agents left in the piping system.

9.3.3 Gas leakage tests

a) The gas storage, chambers, bell and life support systems for gas shall be tested for leakage at themaximum working pressure. The test shall be carried out with the gas type the system is supposedto contain and which has the highest leakage rate properties, or a gas with equivalent properties.Chambers and bells may be tested for leakage using a test gas with only 10% Helium providing a

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thorough inspection of all penetrations is carried out using leak detection ('snooper') liquid recommendedby the industry.

b) A leakage rate up to 1% pressure drop in 24 hours for the whole chamber system can be accepted. Thegas leakage test time shall be minimum 6 hours.

Guidance note:

Note that for systems with max. pressure between 20 bar and 30 bar and chamber temperatures between 20°C and 30°C, atemperature drop of about 3°C will cause a pressure drop of about 1%. (See BS 5355 Specification for filling ratios and developedpressures for liquefiable and permanent gases).


9.3.4 Handling systemsHandling systems shall be subjected to tests for structural strength and for function and power.

a) A static load test to a load equal to the design load (see Sec.6 [3.1]) shall be carried outb) Functional and power testing of normal and emergency systems shall be carried out with a functional

test load of 1.25 times the working weight in the most unfavourable position. It shall be demonstratedthat the systems are capable of carrying out all motions in a safe and smooth manner

c) Monitoring of functional parameters during the test, e.g. pressure peaks in hydraulic systems may berequired.

d) A recovery test of the bell shall be carried out simulating emergency operations conditions.

9.3.5 Life support systemsLife support systems for normal and emergency operation shall be tested for proper functioning.

9.3.6 Various systemsThe following systems shall be tested for proper functioning:

a) sanitaryb) communicationc) fire detectiond) fire alarme) fire extinctionf) evacuation systemsg) diver heating.

Other systems onboard the surface installations, significant for the safety of the diving system, are also to betested.

9.3.7 Electrical systems

a) A test for insulation resistance shall be applied to every circuit between all insulated poles and earth, andbetween individual insulated poles. A minimum value of 1 megaohm shall be attainable.

b) Main and emergency power supplies shall be tested.

9.3.8 InstrumentationThe correct calibration of all essential instrumentation (compartment and bell pressure gauges, gas analysisinstruments etc.) shall be checked.

9.3.9 Environmental control systemsMonitoring system:

a) Failure conditions shall be simulated as realistically as possible, if practicable by letting the monitoredparameters pass the alarm and safety limits. Alarm and safety limits shall be checked.

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Automatic control systems:

a) Normal alterations of the environment shall be imposed and the functions of the system tested.b) A copy of the approved test program shall be completed with final set points and endorsed by the

Surveyor.

9.3.10 Sea trialsThe normal handling system shall be tested with the working weight of the bell or basket to the maximumdepth. For saturation diving systems the bell shall be checked for leakage, and the communication systemshall be tested.

10 Marking and signboards

10.1 GeneralLabels (nameplates) of flame retardant material bearing clear and indelible markings shall be placed so thatall equipment necessary for operation (valves, detachable connections, switches, warning lights etc.) can beeasily identified. The labels shall be permanently fixed.All gas containers shall be marked with a consistent colour code visible from the valve end, showing thename, chemical formula of the gas it contains and the percentage of each gas. Piping systems shall bemarked with a colour code, and there shall be a chart posted in the control room explaining the code.

Guidance note:

Table 2 ISO 32-1977 (E) code proposes:

Name of gas Chemical formula Colour code

Oxygen

Nitrogen

Air

Helium

Oxygen/Helium

mixed gas

Carbon dioxide

O2

N2

He

O2/He

CO2

White

Black

White and black

Brown

White and brown

Grey


10.2 Gas containersEach container shall be permanently and legibly marked on the collar or neck ring (where the thickness ofthe material is greater than the design minimum) as follows:

a) the design codeb) the manufacturer's mark or namec) the manufacturer's serial numberd) the test pressure (bar) and date of hydrostatic teste) surveyor's mark and identificationf) settled pressure (bar) at 15°Cg) volumetric capacity of the container, in litresh) tare weight, i.e. the mass of the container including valve, in kg.

In addition marking of gas content shall be carried out according to [11.1].

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10.3 Other pressure vessels than gas containersEach pressure vessel shall be permanently and legibly marked at a suitable location in accordance with therequirements in the design code. As a minimum the following information shall be present:

a) the design codeb) the manufacturer's mark or namec) the manufacturer's serial numberd) the test pressure (bar) and date of hydrostatic teste) the maximum working pressuref) the inspection body’s mark and identificationg) the maximum set pressure of the safety relief valves.

10.4 Handling systemThe handling system shall, in an easily visible place, be fitted with a nameplate giving the followingparticulars:

a) identification numberb) static test loadc) functional test loadd) working weighte) surveyor's mark and identification.

The above loads shall be specified for each transportation system involved.

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SECTION 2 PRESSURE VESSELS FOR HUMAN OCCUPANCY, GASSTORAGE AND OTHER PURPOSES

1 General

1.1 Objectives

1.1.1 This section aims to give general guidance on:

a) conceptual and detailed design of pressure vessels for human occupancy, for gas storage and for otherpurposes

b) manufacturing of such pressure vesselsc) quality control during manufacturing and fabrication of such pressure vessels including documentation

requirementsd) load conditionse) interlock arrangements for doors and hatches.

1.1.2 For quantitative design parameters and functional requirements, see relevant standards andguidelines, including normative references given in Sec.1 [2] and DNVGL-RU-SHIP.

1.1.3 Further requirements for piping and pipe connections can be found in Sec.7.

1.2 Application and scope

1.2.1 This section applies to all pressure vessels in diving systems designed to comply with this standard.Note that in addition to this standard, and the applied design standards, further national requirements mayapply.

1.2.2 ASME PVHO-1 safety standard for pressure vessels for human occupancy, shall be used for design ofacrylic plastic windows, regardless of which standard is used for the design of the pressure vessel.

1.2.3 Material specifications are given in the applied codes and standards (EN/ASME).

1.2.4 Welding of pressure vessels and general workmanship requirements are not specified herein. Furtherrequirements for welding and workmanship are given in the relevant codes and rules.

1.2.5 This section has impact upon Sec.8, insofar as it provides the basis for design of the pressure vesselsin the hyperbaric evacuation system.

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1.3 DocumentationPressure vessels shall be documented as follows:Plans showing structural arrangement, dimensions, welding seams, attachments and supports of the bell, thechamber and other pressure vessels, with details of doors, locks (medical locks and equipment locks), viewports, penetrations, flanged and welded connections.Plans showing expansion allowances under working conditions for interconnected multi-vessel systems.Documents stating:

a) grade of materialb) welding methods, type and size of filler metalc) design pressured) particulars of heat treatmente) fabrication tolerancesf) extent and type of non-destructive testing of welded connectionsg) type of thermal insulation materials and particulars, i.e.: flammability and specific heat conductivityh) type of buoyancy materials and particulars, i.e. maximum permitted water depth, specific weight,

specific water absorption and buoyancy dependent on water depth and exposure timei) drawings and specifications of all windows with detailed drawings and specifications of the penetration

fitting the appropriate window is to fit. It shall be determined that the tolerances are sufficient includinggaskets, O-rings and retainer rings

j) calculations of thicknesses and or stressesk) fatigue evaluation and if necessary fatigue analysis.

Guidance note:

Provided that the external peak loads does not exceed the strain that can be taken by the pressure vessel flanges, global fatigueanalysis may be omitted by the following action; NDT is carried out to detect surface breaking defects on the external surface ofthe external welds of all the interconnecting trunks and locks in the system at renewal survey.


For seamless steel gas cylinders and vessels:

a) plans showing proposed dimensions and details such as valves and safety devices shall be made for eachtype and size of vessel.

Details shall include:

a) production methodb) eat treatment.

Material specifications for the completed vessel with information on the following:

a) chemical compositionb) tensile strengthc) yield strengthd) elongatione) impact test valuesf) brinell hardness.

The following particulars shall be provided for information:

a) type of gasb) filling pressure at 15°Cc) safety relief valve settingd) weight of empty vessel and volumetric capacity.

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1.4 Testing and marking after completion

1.4.1 The required testing and marking of pressure vessels are specified in Sec.1 [10] and Sec.1 [11] andthe applied standard found in [2.1.2].

1.4.2 Materials selection associated with the production of pressure vessels is covered in the appliedstandard.Requirements and guidance on inspection and monitoring associated with the production of pressure vesselscan be found in the applied standard and DNVGL-RU-OU-0375.

1.5 Material protection

1.5.1 Areas of steel pressure vessels that can be subjected to corrosion shall be protected by approvedmeans. The surface of the window seats cavity shall be protected against corrosion.

1.5.2 Windows mounted on chambers shall be protected to avoid damage by impact and to preventchemicals, which can deteriorate the acrylic plastic, to come in contact with the window from the outside.

Guidance note:

Many solvents for paints, acetone and other agents will deteriorate the acrylic plastic and reduce the strength significantly.


1.5.3 All penetrators in pressure vessels for human occupancy, shall be designed to minimise corrosion fromany fluid passing through them.

Guidance note:

In some cases this requirement may best be met by the use of a sleeve passing through the hull penetration.


1.6 Design loads

1.6.1 The design pressure for chambers and bell shall not be less than that corresponding to the maximumoperating depth as defined in Ch.1 Sec.1 [2.3.37]. The effects of the following loads shall be considered andshall be taken into account if significant:

a) dynamic loads due to movements of the support vesselb) local loadsc) loads due to restrictions in expansionsd) loads due to weight of content during normal operation and pressure testinge) loads due to rough handlingf) loads due to bell and escape tunnel clamped on to the chamberg) the stress evaluation shall apply the distortion theory (von Mises criterion).

Guidance note:

Multipurpose vessels may carry heavy deck loads, which can cause stresses and strains on the mountings of the diving systemcomponents. If this cannot be avoided through design of the installed diving system, it should be monitored during suchoperations.


1.6.2 The design life with respect to fatigue shall be defined by the designer.

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2 General principles for design of chambers and bells

2.1 Chambers

2.1.1 The dimensions of the living compartment shall be sufficient for the diving crew facilities required by[3].

Guidance note:

Statutory requirements may require larger dimensions.


2.1.2 All pressure vessels for human occupancy shall be designed, constructed and tested according to oneof the following codes and standards:

a) EN 13445 unfired pressure vessels.b) ASME VIII div.1 boiler and pressure vessel code.

2.1.3 Diving bells and chambers shall be classified in the highest category in the applied code or standard.

2.1.4 Other codes and standards may be evaluated and accepted on a case by case basis.

2.1.5 All pressure vessels for human occupancy shall be certified.

2.1.6 For diving systems with an operational period exceeding 12 hours, the living compartment is normallyto have a size sufficient for installation of bunks with length and breadth equal to 200 x 70 cm (see Sec.3[9.1.1]). The minimum inner dimensions measured as free height above the deck plates in the middle of thechamber, shall be 200 cm.

2.1.7 All windows in pressure vessels for human occupancy shall be certified.Guidance note:

VL certificates will be required.


2.1.8 All compartments shall be fitted with windows, which allow internal areas to be viewed from outside.

2.1.9 For diving systems, the living compartment and other compartments that can be used fordecompression including the bell, shall be provided with means for locking in provisions, medicine andequipment necessary for the operation of the system. The divers in each living compartment shall haveaccess to toilet facilities. Paints, cabling and other materials shall be considered for toxic or noxiousproperties as specified in Sec.1 [8.3].

2.2 Bell

2.2.1 The bell shall be provided with proper protection against mechanical damage.

2.2.2 The bell shall be provided with windows that as far as practicable allow the occupants to observe diversoutside the bell.

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2.2.3 The bell shall be equipped with one extra external lifting fastening.Guidance note:

Note that the design and location of the extra lifting fastening needs to be considered in view of the need to bring the bell back toa mating trunk on the decompression chambers as required by Sec.6 [2.2.1].


2.2.4 Internally there shall be an attachment at the top for lifting of divers.

2.2.5 Bells shall have possibilities for entry and exit when landed on the seafloor in an arbitrary manner, inan emergency. When the bell is fitted with drop weights, release of these in two stages may be accepted,when the first stage allows the bell to rise sufficiently for entry and exit. (Note guidance to Sec.6 [2.3.1)

2.3 Doors, hatches, windows, branches etc.

2.3.1 Minimum dimensions of doors, hatches and medical locks.Doors and hatches for human transportation shall in general be:

a) minimum diameter 600 mm, andb) minimum diameter 800 mm for lock-out and lock-in hatches on the bell. The length of the bell hatch

trunk shall not exceed the diameter.Guidance note:

For doors and hatches in between chambers, standard pipe with nominal bore 24" may be acceptable.


2.3.2 The medical locks shall be large enough to allow lock-in and lock-out of CO2 absorption material andnecessary supplies for the divers.

Guidance note:

National rules and requirements may be more stringent and thereby take precedence (i.e. Norwegian Petroleum Directorate).


2.3.3 Means enabling the doors to be opened from either side shall be provided.Guidance note:

As the above requirement also applies to the internal doors in chamber complexes, it does follow that locking devises are notallowed on the pressurised side of these doors unless they can be operated from the other side. Clip locks are frequently used onthese doors to prevent slamming due to the vessels movement in the sea. However, the clip setting should be such that they canbe pushed/pulled open from either side without the use of excessive force.


2.3.4 For:

a) doorsb) hatchesc) mating arrangementsd) pressurised locks and trunkse) pressurised containersf) accompanying equipment under pressure

where opening or unintentional pressure drop may entail danger or cause injury, the closing mechanismsshall be physically secured by locking mechanisms (interlocks).

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This applies to units which do not seal by pressure and includes, but is not limited to:

a) mating arrangements between bells and transfer compartmentsb) mating arrangements between hyperbaric lifeboats and escape trunks where these are installedc) equipment locksd) medical lockse) soda lime (CO2 scrubber) containers for external regeneration of the chamber environments.

2.3.5 The closing mechanisms with accompanying locking mechanisms shall be arranged so that:

a) opening cannot take place unless the pressures are equal on both sides or unless the pressures in theunits are at ambient level

b) correct position of the closing mechanisms and the locking mechanisms shall be ensured before it ispossible to apply pressure

c) the pressures in the units, shall directly control the locking mechanisms, andd) the penetrators and piping for pressure sensing shall be arranged so that blockage is avoided.

2.3.6 Trunks between doors shall be equipped with pressure equalising valves. Penetrators for pressureequalising shall be arranged so that blockage is avoided.

2.3.7 Where mountings are secured by studs, these shall have full thread holding in the shell for a length ofat least one diameter. Holes for studs shall not penetrate the shell.

2.3.8 Windows with a diameter above 500 mm and thickness less than 90 mm shall be protected againstimpact. Impact protection may be provided by:

a) recessing the external surface of the window at least 50 mm below the surrounding structureb) one or more external bumpers extending across the window.

2.3.9 Damage control plugs may be provided to enable the divers to seal off windows to prevent damage orleakage developing. One plug for each size window in each compartment may be sufficient.

2.3.10 For pressure vessels where fatigue can be a possible mode of failure, attention shall be given to thepossible adverse effects of the following design features:

a) pad type reinforcement of openingsb) set-on branchesc) partial penetration welds of branches.

Guidance note:

Provided that the external peak loads does not exceed the strain that can be taken by the pressure vessel flanges, globalfatigue analysis may be omitted by the following action: NDT is carried out to detect surface breaking defects on the externalsurface of the external welds of all the interconnecting trunks and locks in the system at renewal survey


3 Welded pressure vessels, materials and fabrication

3.1 Materials

3.1.1 Steel grades shall comply with the applied design code and standard.

3.1.2 Other material grades may be acceptable after special consideration. In such cases, additional testingmay be required and qualification procedures shall be reconsidered.

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3.1.3 Materials for main pressure retaining parts are normally to be delivered with the manufacturer's workscertificates (W), as a minimum.

Guidance note:

Product certificates, PC, may be required in the contract or the terms of delivery.


3.1.4 Stainless steel cladding, stainless steel tubes, fittings etc. which are welded to pressure vessels ofnon-stainless steel shall be of a stabilised or low-carbon grade. Acceptable grades are given in the applicablestandards or in DNVGL-RU-SHIP Pt.2 Ch.2 Sec.4 and Sec.5.

3.2 Fabrication

3.2.1 Pressure vessels for diving systems shall be manufactured by works approved by a recognised body,for the production of the type of pressure vessels being delivered.

3.2.2 Welding shall be carried out according to approved drawings.Qualification of welders, welding procedure specifications, welding procedures and testing shall be accordingto the applied design code or standard.

3.2.3 The following tests have to be carried out in addition to the tests specified in the applied design codeor standard:

a) all butt welds in diving bells and chambers shall be radiographed over their full lengthb) branches and reinforcement of openings, including all weld connections to the shell, shall be subjected to

100% magnetic particle testing.

3.2.4 When the applied code or standard requires heat treatment of dished ends after hot or cold forming,mechanical testing may be required after the final heat treatment. The details between intermediate headsand cylindrical shells of chambers may be done in accordance with requirements given in,

a) EN 1708-1:2010 welding, basic weld joint details in steel Table 9: internal diaphragms and separatorsb) ASME Sec.VIII div.I Fig. UW-13.1.

The outside diameter of the head skirt shall have a close fit to the cylinders.The butt weld and filled weld shall be designed to take shear based on 1.5 times the maximum differentialpressure that can exist. The allowable stress value for the butt weld shall be 70% of the nominal designstress for the shell material and that of the fillet weld 50%. The area of the butt weld in shear shall be takenas the width at the root of the weld times the length of the weld. The area of the fillet weld shall be taken asthe minimum leg dimension times the length of the weld.

3.2.5 The surface dimensions and finish of sealings and seals for hatches and windows are generally tocomply with the tolerances specified by the manufacturers of the windows and the sealing systems.

3.2.6 Flat disc windows shall have a bearing gasket between the window and its seat. This gasket shall serveas a secondary seal. The gasket shall be bonded to the seat.The retainer ring shall provide adequate initial compression of the sealing arrangement to compensate forthe displacement of the window due to the pressure. The minimum seating diameter in relation to windowdimensions shall be specified.The included conical angle of the seating surface of conical flanges shall be within + 0.00 or -0.25 degrees ofthe nominal value.

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The surface finish of seats of metallic materials for conical-, double bevelled disc and spherical shell windowsshall have an average roughness less than R. = 1.5 μm.

3.2.7 Before installation of a window in its flange, complete cleanliness of the seating surfaces shall beensured. The seating surface and any o-ring grooves shall be lubricated with an oxygen compatible lubricant.Mineral oil lubricants shall, under no circumstances, be used for this purpose.

3.3 Fabrication tolerances

3.3.1 Fabrication tolerances shall meet the requirements in the applied codes and standards.

3.3.2 Local tolerance requirements for ring frames are given in Figure 1, for vessels subject to externalpressure.

Figure 1 Maximum deviations for ring stiffeners.

4 Strength of welded pressure vessels

4.1 Structural analysis

4.1.1 Pressure vessels shall be documented by structural analysis for specified design conditions according tothe applied codes and standards.

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4.1.2 For details not covered by the applied codes and standards, finite element analysis may be acceptableif properly planned, modelled and documented.Alternatively, by applying strain gauges, stress measurements may be carried out according to an approvedprogramme and shall be properly documented. The tests shall be planned, and carried out during the firstpressure test.

4.1.3 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of fullpressure cycles as defined by the designer [1.6.2]. The evaluation and analysis shall be carried out accordingto the applied design code and standard.

Guidance note:

NDT of the surface of the external weld of the large openings such as windows and locks to detect surface braking defects shouldbe carried out the renewal survey.


4.2 Vessels subjected to external pressure

4.2.1 Frames and panels supporting pressure-retaining parts shall be designed for a force of minimum 1.2times the actual load.

4.2.2 Additional stresses shall be within the limits given in the applied design code or standard, for combinedstresses.

4.3 Flanges for windowsFlanges for windows with conical seating shall have dimensions preventing the flange deformations to exceedthe following limits when window and pressure vessel is subjected to the design pressure :

— radial: 0.002 times the smaller diameter of the acrylic plastic window, and— angular: 0.5°.

5 Gas cylinders

5.1 General

5.1.1 Gas cylinders shall be produced by manufacturers authorised for such production and certified by acompetent inspection body when:

where:p = design pressure in bar.V = volume in m3.The certification level shall as a minimum be manufacturer's works certificates (W). Other levels ofcertification may be required by the terms of delivery.Smaller gas cylinders shall be certified if they provide an essential function in the system.

Guidance note:

Cylinders on-line in a system providing breathing gas to the divers will be considered essential.


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5.1.2 The materials applied shall be certified as a minimum by the manufacturer's works certificates (W).Other material certificates may be required by the terms of delivery.

5.1.3 They shall be designed, constructed and tested according to one of the following standards, norms ordirectives:

a) EN ISO 9809-1 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing,part 1: quenched and tempered steel cylinders with tensile strength less than 1100 MPa.

b) EN ISO 9809-2 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing,part 2: quenched and tempered steel cylinders with tensile strength greater than or equal to 1100 MPa.

c) EN ISO 11120:1999 gas cylinders, refillable seamless steel tubes for compressed gas transport, of watercapacity between 150 l and 3000 l, design construction and testing.

Guidance note:

For permanent installations within EU, the directives apply as regulations. (See EU directive 2010/35/EU.)


5.1.4 Shell thickness shall meet the criteria given in the applied code or standard for test pressure. Theworking pressure for a given geographical area is given by reference to a standard such as EN 13096Transportable gas cylinders - Conditions for filling gases into receptacles and EN 13099 transportable gascylinders, conditions for filling gas mixtures into receptacles, single component gases.

5.1.5 Corrosion allowance shall be specified in the terms of delivery reflecting the intended use of the gascylinder, but shall not be less than 1 mm.

Guidance note:

Gas cylinders without any corrocion allowance may be accepted based on the limitation that no repair will be allowed in case ofinternal or external corrosion. The use of such cylinders require acceptance by the end user.


5.2 Heat treatmentHeat treatment shall follow the requirements given in the applied code or standard, and shall bedocumented.

5.3 Tolerances and surface conditionsTolerances and surface condition shall meet the criteria given in the applied code or standard, and shall bedocumented in the design documentation. If the applied code or standard does not specify requirements fortolerances and surface conditions, then it may be necessary to specify this in the terms of delivery.

5.4 Production testsProduction tests shall be carried out in accordance with the requirements given in the applied code orstandard. Further production tests, and required attendance during testing, may be specified through theterms of delivery.

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6 Acrylic plastic windows

6.1 General.The following requirements apply to windows made from cast stock of unlaminated polymethyl methacrylateplastics, in the following denoted acrylic plastic, with a design life of 10 years, suitable for:

a) 10.000 load cyclesb) sustained temperatures in the range specified by the end user but not less than specified by ASME

PVHO-1c) pressurisation or depressurisation rates not exceeding 10 bar/secondd) use in environments that cannot cause chemical or physical deterioration of the acrylic plastic (i.e.

resistant against saltwater and gases used in life support systems).

6.2 MaterialsMaterials for acrylic plastic windows shall be manufactured and tested in accordance with ASME PVHO-1safety standard for pressure vessels for human occupancy.

6.3 Manufacturers of cast materialManufacturers wishing to supply cast acrylic plastic for diving systems, shall be approved for such production.The material shall have an approved chemical composition and to be produced, heat treated and testedaccording to the ASME PVHO-1 safety standard for pressure vessels for human occupancy. Approval shall begranted on the basis of a thorough test of material from the current production and a report after inspectingthe works, and verification of QA and QC against requirements given in ASME PVHO-1.

6.4 Certification of cast material

6.4.1 Each delivery of cast material shall be accompanied by a certificate issued by the manufacturer(PVHO-1 forms VP-3 and VP-4). The certificate shall (as a minimum) contain the following:

a) name and address of manufacturerb) certificate number and datec) designation of productd) numbers and dimensions of the pieces covered by the certificatee) material test results and propertiesf) signature.

6.4.2 The following text shall be printed in the right uppermost corner of the certificate: this certificatewill be accepted by (approval body) on the basis of completed approval tests and the (approval body’s)surveillance of production control and products. The manufacturer guarantees that the product meets therequirements of (approval body) and that inspection and tests have been carried out in accordance with(code or standard)

6.4.3 The cast material shall be marked with the manufacturer's name and with the number and date of thecertificate.

6.4.4 If a later edition of the ASME standard requires further documentation and markings, the ASMErequirements shall be met.

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6.5 Certification of windows

6.5.1 Each batch of acrylic plastic windows used in diving systems shall have a certificate issued by theapproval body, showing the test results and the annealing conditions according to the standard.

6.5.2 Each window shall have an identification marked on it for traceability. Identification of each windowshall include: design pressure, maximum temperature, initials for P.V.H.O., window fabricator's identificationmark, fabricators serial number and year of fabrication.For ease of viewing, the above information shall be located on the windows seating surface with an indeliblemarker. Acceptable marking methods are given in ASME PVHO-1.Stamping or marking that can cause crack propagation is not permitted.

6.6 Geometry and thickness

6.6.1 Windows shall be of the standard designs according to the ASME PVHO-1 safety standard for pressurevessels for human occupancy.

6.6.2 Windows for two-way pressurisation shall meet the requirements applicable to one-way windows inboth directions. For double bevelled disc windows, not more than 50% of the thickness shall be utilised indetermination of short term critical pressure.

6.6.3 O-ring grooves shall not be located in window bearing surfaces serving primarily as support or in theacrylic window itself.

6.7 Fabrication

6.7.1 The included conical angle of the seating surface of a window shall be within +0.25/-0,00 degrees ofthe nominal value.

6.7.2 The deviation of a spherical window from an ideal sphere shall be less than 0.5% of the specifiednominal external radius of the spherical section.

6.7.3 Each window shall be annealed after all forming and polishing operations are completed. The annealingprocess shall be according to the annealing schedule in ASME PVHO-1.

6.7.4 During the manufacturing process each window shall be equipped with identification and amanufacture process rider for recording of all pertinent data.

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SECTION 3 LIFE SUPPORT SYSTEMS

1 General

1.1 Objectives

1.1.1 This section aims to give general guidance on:

a) conceptual and detailed design of life support systemsb) manufacturing of life support systemsc) quality control during manufacturing and fabrication of components and subsystems for life support

systems.

1.1.2 The section presents key-issue requirements for gas distribution capacities, environmental conditioningand oxygen systems. Documentation requirements are identified.

1.1.3 Design and acceptance criteria include capacities for gas storage, choice of valves and fittings forcertain applications, environmental control parameters, breathing resistance for CCBS and diving crewfacilities.

1.1.4 Requirements for the design of oxygen systems are aimed at reducing the hazards posed by flash fires.

1.1.5 This section contains requirements to ensure safe arrangements in pressurised systems and controlstations.

1.1.6 Further requirements for pipes, hoses, valves and fittings are given in Sec.7.

1.1.7 Requirements for shut off valves, pressure relief and drainage are aimed at ensuring the safeguard ofpersonnel and plant, as are the requirements for alarm systems.


1.2.1 For quantitative design parameters and functional requirements, see relevant standards andguidelines, including DNVGL-RU-SHIP.

1.2.2 Requirements for testing are given in Sec.1 [9].

1.2.3 Requirements for installation are only rudimentary.

1.2.4 This section has an impact on all other sections in this chapter.

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1.3 DocumentationLife support systems shall be documented as follows:

a) Plans showing schematic arrangement of all piping systems.b) Documents stating:

— material specifications— maximum working pressure— dimensions and thickness— contained fluids— type of valves and fittings— specifications of flexible hoses.

c) Plans (diagrams) showing arrangement and giving specifications of the gas storage and supply (gasbanks, compressors, boosters etc.).

d) Plans showing the arrangement and giving specifications on environmental control systems andequipment (heating, CO2-absorption, circulation), diving crew facilities, sanitary and drainage systems.

e) Component lists, with specifications on make and type and documentation on any tests carried out onall equipment used in the life support system. Plans showing cross-section and giving particulars onmaterials and dimensions of umbilical.

f) Calculations showing the heat and cooling consumption for the system under given environmentaltemperatures.

g) Description of proposed cleaning procedure for breathing gas system.

2 Gas storage

2.1 Capacity

2.1.1 There shall be a permanently installed gas storage plant or suitable space for portable gas containers.The size of the containers or space shall be sufficient to provide the divers with adequate quantities of gasesfor operation at maximum operating depth for both normal and emergency modes.

2.1.2 The minimum gas storage capacity of fixed installed containers or space for portable containersintended for emergency operations shall be sufficient to:

a) Pressurise the inner area once and the bell(s) and transfer compartments once more to maximum depth,dmax, with suitable breathing gas, and

b) For diving systems with an operational time exceeding 12 hours it shall provide suitable gas to pressurisethe largest compartment once, to dmax.

c) Maintain a proper oxygen partial pressure in the inner area and supply for masks for at least:

i) 24 hours, diving systems with an operational time not exceeding 12 hours orii) 48 hours, diving systems with an operational time exceeding 12 hours.

d) For pure oxygen, the minimum volume may be taken as:

i) 2 Nm3 for each diver for a diving system with an operational time not exceeding 12 hours orii) 4 Nm3 for each diver for diving systems with an operational time exceeding 12 hours.

1 Nm3 is given as 1 cubic metre of the gas at 0°C and 1.013 bar standard condition.

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2.1.3 For emergency use of masks there shall be sufficient facilities to supply adequate quantities of gases.The facilities shall be capable of providing a relevant delivery rate both at maximum depth and duringdecompression. The containers required by 102 may be used also for these emergency purposes.Adequate quantities may be taken as a minimum of:

a) 2 m3 at the pressure of the inner area with an oxygen partial pressure between 0.18 and 1.25 bar foreach diver, and in addition

b) 15 m3 at the pressure of the inner area with an oxygen partial pressure between 1.5 and 2.5 bar atdepths greater than 18 m, to each of the maximum number of divers in one of the living compartmentsfor diving systems with an operational time exceeding 12 hours.

2.1.4 The storage capacity for emergency gas shall be provided in separate containers, and shall not beincluded in the containers for current gas supply.

2.1.5 The bell shall have a self-contained emergency gas storage with minimum capacity to supply thefollowing:

a) 1 Nm3 oxygen for each diverb) suitable breathing gas mixtures. The capacity shall be the greater of the two:

— that which is sufficient to empty a bell filled with 40% water at dmax— that which is sufficient to supply each of the bell divers with suitable breathing gas for 15 minutes.

The gas volume respirated by one diver in 15 minutes may be taken equivalent to 0.8 m3 at ambientpressure dmax.The minimum gas storage volume, Vg (m

3), of deep mix on the bell considering a minimum overpressure inthe containers, and sufficient time for the operations to avoid significant temperature differences, may beestimated as follows:

whereV = volume (m3) at ambient pressure dmax of the supply to the divers or 0.4 times the internal volume

of the bell.pg = pressure (bar) in gas storage containers.pb = pressure (bar) in the bell corresponding to the depth.

2.2 Shut-off, pressure relief and drainage.

2.2.1 Pressure vessels shall be fitted with over pressure relief devices and shut off valves except as providedfor in [5.2] and [5.3].

2.2.2 Pressure vessels without individual shut-off valves and with: pV < 50, installed in groups with a totalpV < 100, can have a common overpressure relief device and shut-off valve.p = design pressure in barV = volume in m3 (standard conditions)

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2.2.3 For gas storage of breathing gases and oxygen, the pressure relief device shall be a safety valve.Safety valves shall be set to open at a pressure approx. 3% above the developed pressure at 55°C, basedon filling the cylinders at 15°C to maximum filling pressure. The total relieving capacity shall be sufficient tomaintain the system pressure at not more than 110% of design pressure.Developed pressure under above-mentioned conditions may be taken as given in reference to a standardsuch as

a) EN 13096 transportable gas cylinders, conditions for filling gases into receptacles, single componentgases.

b) EN 13099 transportable gas cylinders, conditions for filling gas mixtures into receptacles.

2.2.4 Containers where water can accumulate shall be provided with drainage devices (e.g. volume tanksand filters)

3 Gas distribution

3.1 General

3.1.1 The gas distribution system consists of all components and piping necessary for distribution of gas fornormal and emergency operations.Piping for gas and electrical cables shall be separated.

3.1.2 The distribution system to each compartment shall facilitate:

a) two independent alternatives for pressurisation with a minimum pressurisation rate of 2 bar/minute to 2bar and at 1 bar/minute thereafter

b) depressurisationc) decompression rate of minimum 1 bar/minute at pressures exceeding 2 bar for saturation diving systemsd) maintenance of a suitable breathing atmosphere in the inner area (when adding pure oxygen to the

compartments, a separate piping system shall be provided)e) supply of suitable breathing gas for masks (for saturation diving systems this supply shall be

independent for each living compartment)f) exhaust from masks intended for oxygen if a closed circuit breathing gas system is not used.

3.1.3 There shall be two independent supplies of gas to the bell umbilical.

3.1.4 Filters and automatic pressure reducers shall be so arranged that they can be isolated withoutinterrupting vital gas supplies.

3.1.5 Valves in piping systems to masks, bells and divers in water shall be so arranged that:

a) leaking valves cannot cause unintentional gas mixturesb) oxygen cannot unintentionally be supplied to other piping systems than that intended for oxygen.

3.1.6 The discharge from overpressure relief devices and exhaust shall be led to a location where hazard isnot created.

3.2 Bell

3.2.1 The bell and the lock-out diver(s) shall have a normal supply and an independent self-containedemergency supply from the bell.

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3.2.2 The breathing gas system supplying the personal umbilical to the stand-by diver in the bell shall bearranged for an alternative supply, independent of the lock-out diver(s)'s normal supply. The bells onboardgas supply may be accepted for this purpose.

3.2.3 The bell shall be equipped with two alternatives for exhausts. One shall be arranged so that a diverwho intends to aid his entering by a partial flooding of the bell can operate it from the lower part insidethe bell. The exhaust systems shall not permit a flooding above electrical equipment when the bell is in anupright position.

3.2.4 The exhaust system shall be designed to enable removal of the water in case of a tilted bell with closedhatch and trapped water inside.

Guidance note:

The degree of tilt envisaged may vary from one bell design to another and will therefore need to be considered in each case. Sidemated bells will most likely tilt more than bottom mated bells. As this requirement is normally simple to fulfil by means of a flexiblehose, it is thought that a 60° list should be considered minimum.


3.2.5 The exhaust system not intended for partial flooding of the bell shall be fitted with a spring-loadedvalve that closes when the valve handle is released.

3.2.6 The bell shall be equipped with masks corresponding to the number of divers plus one. The masks shallbe arranged for supply from normal and emergency supply alternatively. Diving masks and diving helmetswith gas supply are accepted as masks.

3.2.7 The emergency oxygen supply system shall be designed to enable the maintaining of a proper partialpressure of oxygen inside the bell by a dosage system.

3.2.8 Automatic pressure reducers for breathing apparatuses shall be fitted.

3.2.9 Bell shall be fitted with an emergency manifold at a suitable point close to the main lifting attachmentwhich shall include connections for the following services:

a) 3/4 inch NPT (female) - for hot waterb) 1/2 inch NPT (female) - for breathing mixture.

The manifold shall be clearly marked and suitably protected.

3.3 Chambers

3.3.1 Each living compartment shall be equipped with breathing masks corresponding to the maximumnumber of divers for which the chamber is rated plus one. The masks shall be arranged for breathing fromeach bunk. For diving systems with an operational time exceeding 12 hours, transfer compartments to thebell(s) shall be equipped with a number of masks at least corresponding to the maximum number of divers inthe bell plus one. Other compartments shall have at least 2 masks.

3.3.2 The masks shall be permanently connected or easily connectable to piping systems for supply of thegases according to [2.1.3].

3.3.3 The exhaust sides of the masks intended for oxygen shall be connected to external dump, or to be of aclosed circuit type.

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3.3.4 The mask systems shall be secured against inadmissible pressure drop on the exhaust side.

3.3.5 The gas supply system shall be arranged to ensure homogenous gas content in the inner area.

3.4 Stand-by diver at surfaceA piping system for supply of breathing gas to a possible stand-by diver at surface shall be arrangedseparated from the divers' supply.

4 Oxygen systems

4.1 General

4.1.1 Oxygen shall be stored and distributed in containers and piping systems exclusively intended foroxygen systems.

4.1.2 Containers for oxygen shall be stored in open air or in rooms exclusively intended for oxygen. Therooms shall be separated from adjacent spaces and ventilated according to Sec.5 and shall be fitted with anaudio-visible oxygen alarm, at a manned control station.

4.1.3 The pressure in the oxygen systems shall be reduced from storage pressure to the minimum pressurenecessary for proper operation. The pressure reduction shall be arranged as close as possible to the storagecontainers.

Guidance note:

A maximum pressure of 40 bar will normally be accepted when dmax is less than 350 m.


4.1.4 Oxygen shall not be stored or ducted in any form close to combustible substances or hydraulicequipment.

4.1.5 Oxygen dumped from the diving system shall be ducted to a safe dumping place.

5 Piping systems

5.1 General

5.1.1 Low-pressure systems supplied from high-pressure system shall be provided with pressure reliefvalves. The total relieving capacity shall be sufficient to maintain the system pressure at not more than110% of design pressure. The relief device shall be located adjoining, or as close as possible, to the reducingvalve.

5.1.2 All systems shall be provided with means of manually relieving the pressure.

5.1.3 Filters shall be provided on the high-pressure side of gas systems.

5.1.4 Pipe ends in chamber and bell shall be arranged so that injuries due to suction are avoided.

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5.1.5 All pipe penetrations in the chambers and bells shall be fitted with external and internal shut-off valvesmounted directly on the shell plating. Valves may be mounted close to chamber shells, provided that thepiping between the chamber and valve is well protected and has a minimum thickness according to the rules.

5.1.6 Threaded pipe penetrations are only acceptable for external diameters equal to or less than M30 (1"NPT threads/1" BSP treads).

5.2 BellBells shall be fitted with an overpressure alarm.

5.3 Chambers

5.3.1 In addition to the requirements in [5.1.5] all penetrations for lines designed for gas distribution (e.g.supply, exhaust and equalisation) shall be fitted with non-return valves or flow fuses as appropriate for thedirection of gas flow. Lines specifically designed for non distribution purposes (e.g. analysis) shall be kept tothe minimum diameter possible and limited to a maximum of 5 mm.

5.3.2 The piping between externally mounted non-return valve or flow-fuse and the external shut-off valveshall be well protected and have minimum thickness according to Sec.7.

5.3.3 The compartments shall be fitted with a safety valve or a visual and audible overpressure alarmalerting the operators at the control station.Penetrations for safety valves shall be provided with shut-off valves on both sides of the shell plating. Theseshut off valves shall be sealed in the open position. Any safety valves shall be set to open at a pressure ofapprox. 3% above the design pressure.

5.3.4 Valves in chambers designed for holding water (i.e. hyperbaric training centres) shall be considered ineach case.

6 Environmental conditioning in bell and chambers

6.1 Heating of bell

6.1.1 Bells shall have a normal heating system with controls and capacity sufficient to maintain acomfortable temperature for the divers in the bell and in water. The heating system shall be fitted with atemperature indicator.

6.1.2 For deep diving, provision for heating the divers' gas shall be provided.

6.1.3 For diving systems with an operational time exceeding 12 hours, the heating supply systems shall beprovided with full redundancy. This includes full redundancy in the event of a possible loss of main power(Sec.4 [2.4.1]).

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6.1.4 Bells shall have emergency means of preventing excessive heat loss by the divers for a period of 24hours at dmax., and shall be independent of the main umbilical.

Guidance note:

This can be achieved by heating the bell environment, the divers directly by heated suits, or by passive thermal insulation as wellas heating the divers' breathing gas by active or regenerative methods.


6.2 Heating and cooling of chambers

6.2.1 Systems for heating the living compartments shall be arranged.

6.2.2 For saturation diving systems, all compartments shall have an arrangement for heating. The livingcompartments shall be provided with a system for heating and cooling, enabling temperature regulationwithin +/- 1°C from set point under steady conditions. Heating and cooling systems shall be provided withfull redundancy.

6.2.3 Heating coils on the outside of the chambers shall have a minimum of two independent temperaturecontrols of the power circuit.

6.3 Humidity reduction in chambersA system to reduce the humidity in the living compartments shall be provided. For saturation diving systems,a relative humidity of 50% shall be maintainable under steady conditions.

Guidance note:

For certain geographical regions this requirement is hard to fulfil unless additional coolers supplement the regular environmentalcontrol systems or some other compensation is provided for. This needs to be considered in each case.


6.4 Noise reduction

6.4.1 Silencers shall be fitted and the system shall be so designed that the divers cannot be exposed toharmful noise levels.

Guidance note:

IMO resolution A.468 (XII) code on noise levels onboard ships.


6.4.2 Silencers shall be fitted with shields which provide protection against possible fragmentation but whichdo not affect the gas flow.

6.5 Gas circulation systems for chambers

6.5.1 Internal circulation systems for gas in the chambers shall be such that a homogeneous gas content isensured.

6.5.2 Pressurising and exhaust systems shall be arranged to ensure an even mixing of gas.

6.5.3 The circulation system shall have sufficient capacity to avoid stratification of gas layers in thechambers and maintain a homogenous gas mix at the set operational parameters.

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6.5.4 Materials shall be considered for toxic or noxious properties as specified in Sec.1 [9.3.5].

6.6 Removal of carbon dioxide

6.6.1 Carbon dioxide removal systems or atmospheric renewal systems shall be arranged for the bell andeach living compartment. For saturation diving systems, all compartments shall be arranged with redundancyin carbon dioxide removal systems.

6.6.2 Carbon dioxide removal systems or atmospheric renewal systems for normal operation shall havethe capacity to maintain the partial pressure of carbon dioxide below 0.005 bar continuously based on aproduction rate of 0.05 Nm3 per hour per diver.

6.6.3 The bell shall have a self-contained, self-powered emergency absorption system with a capacity tokeep the partial pressure of carbon dioxide below 0.02 bar for 24 hours.

6.7 Regeneration of pure helium

6.7.1 Systems for regeneration of pure helium for further use in the system shall ensure only a limitedcontent of contaminants. The system shall be capable of maintaining the nitrogen content below a partialpressure of I bar at the maximum operating depth of the diving system. For welding operations the collectiveargon and nitrogen content shall be considered.

6.7.2 Water traps for gas reclaim shall be designed for simplicity of cleaning, disinfecting and drying.

7 Gas control systems

7.1 Control stands

7.1.1 Requirements for instrumentation are given in Sec.4.

7.1.2 The control stands shall have means for:

a) choice between gas storage containersb) pressurising and pressure regulation of each compartment independentlyc) decompression of each compartment independentlyd) equalising the pressure between compartmentse) controlling oxygen flow to compartments independentlyf) controlling oxygen and mix gas supply to masks in each individual compartmentg) controlling gas supply to bell.

7.2 Helium and oxygen mixing systems for direct supply for breathing

7.2.1 Systems for mixing of helium and oxygen for subsequent direct supply for breathing shall beautomatic, to have an automatic control system, an automatic alarm system and an automatic safetysystem.

7.2.2 As an alternative to [7.2.1], the inclusion of a large volume tank is considered to provide an equivalentlevel of safety as that prescribed by the requirements for automation and independence in [7.2.4]. Theremaining requirements shall be met.

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The volume tank shall be such that the prescribed tolerances for partial pressures downstream are notdeviated from within the first hour after the analysers have alerted the operator that the upstream mixture isout of the tolerated range. The alarm shall be audio-visual at a manned control station.

Guidance note:

Prescribed tolerances is normally understood to be gas having an oxygen partial pressure in the range 0.21 bar to 1.7 bar asrequired by NPD whereas the dive control alarm will be a tolerance of +/-0.03 bar about the desired set point.


7.2.3 The control system shall keep the mixture at a pre-set value within the prescribed tolerances.Maximum tolerances: +/- 0.03 bar, partial pressure O2.

7.2.4 The safety system shall be independent of the control system and shall incorporate changing of thesupply automatically to a premixed suitable breathing gas if tolerances are exceeded. The safety system shallensure a constant delivery of suitable breathing gas to the diver during all operating conditions, taking intoaccount the characteristics of components in the systems such as response time for gas analysers etc.

8 Closed circuit breathing systems (CCBS)

8.1 General

8.1.1 Installation of CCBS is not required as a condition for the standard. If such system is installed, it is,however, to comply with the following requirements.See: guidelines for minimum performance requirements and standard unmanned test procedures forunderwater breathing apparatus by: U.K. Department of Energy and Norwegian Petroleum Directorate. Testsmay be carried out in accordance with the guidelines.

8.1.2 System particulars

a) The maximum work of breathing (w) shall not exceed 3.0 Joules/litre measured at a standard breathingrate, respiratory minute volume (RMV) of 62.5 litres/minute.

Guidance note:

Work of breathing should be as low as possible. A preferred level would be below 1.75 Joules/litre at an RMV of 62.5 litres/minute.


b) The system shall be able to work satisfactorily over a range of RMV's up to 75 litres/minute. For testpurposes the system should function to 90 litres/minute.

c) The variation in respiratory pressure (ΔP) should be limited to 1.5 kPa and shall not exceed 2.5 kParelative to the reference pressure (PR). Reference pressure(PR) is the equilibrium pressure measuredat the level of the divers mouth when there is no gas flow. Respiratory pressure (ΔP) is the differentialpressure measured at the divers mouth, during inhalation and exhalation, measured relative to thesystem reference pressure.

d) The hydrostatic imbalance (PR- PLC) varies with the orientation of the diver and the position of thedemand valve (or equivalent device) and has an effect on the work of breathing. The hydrostaticimbalance shall not be outside the range of -3.5 kPa to + 2.0 kPa.

Guidance note:

Ideally, the hydrostatic pressure imbalance should be between -2.0 kPa and + 1.0 kPa. PR is the reference pressure at thedivers mouth and PCL is the lung centroid pressure, which is defined as the pressure which restores the lungs to their normalresting volume. PCL is measured at a position 19 cm inferior and 7 cm posterior to the suprasternal notch.


e) The system shall be designed so as to minimise the build up of carbon dioxide. Dead space volumeshould be as low as possible. The partial pressure of carbon dioxide (ppCO2) shall be limited to 1 kPa.

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Guidance note:

The volume of oronasal mask or equivalent device should be less than 200 ml.


8.1.3 CCBS shall be automatic with normal and safety functions according to [7.2] including automaticcontrol of carbon dioxide partial pressure.

8.1.4 If the equipment fails, the lung over or under pressure should be as low as possible, but shall notexceed 6.0 kPa relative to the lung centroid pressure.

8.1.5 CCBS shall have an emergency mode by free exhalation, i.e. without the use of the exhaust line.

8.1.6 CCBS shall incorporate temperature regulation system for inhaled gases.Guidance note:

1 kPa = 1000 Pascal

1 Pascal = 1 N/m2 = 10-5 bar


9 Diving crew facilities

9.1 General

9.1.1 One bunk shall be provided for each diver in the living compartment permitting the diver to restcomfortably. For DSV-SAT systems the bunks shall measure at least 200 x 70 centimetres .

9.1.2 Proper lighting shall be provided in all compartments and bell.

9.1.3 The bell shall be fitted with emergency lighting.

9.1.4 If flush type toilets are installed, the systems shall be designed so that drainage cannot take placeduring sitting use. (See also the requirements for safety locks given in Sec.2 [2.3.4] and [2.3.5]).

9.1.5 Sanitary systems connected to external systems shall be designed to avoid an unintentional pressurerise in the external system in case of malfunction or rupture of the diving systems' sanitary systems.

9.1.6 One toilet and one shower with hot and cold water are required per pressure level. The toilet may beflush type or disposable bag type. In connection with the toilet there shall be a scavenging or cleaning facilityto get rid of bacteria and odour. The shower and the toilet shall be located in a room separated from theliving compartment.

9.1.7 The living compartment shall provide space for a table.

9.1.8 One toilet and one shower with hot and cold water are required per pressure level. The toilet may beflush type or disposable bag type. In connection with the toilet there shall be a scavenging or cleaning facilityto get rid of bacteria and odour. The shower and toilet shall be located in a room separated from the livingcompartment.

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SECTION 4 ELECTRICAL, INSTRUMENTATION ANDCOMMUNICATION SYSTEMS

1 General

1.1 Objective

1.1.1 The purpose of this section is to specify additional requirements for electrical systems and equipmentserving diving systems. Emphasis is placed on the special needs associated with the design and manufactureof diving systems, whereas general requirements for electrical systems and components are given in DNVGL-OS-D201 electrical installations and DNVGL-OS-D202 instrumentation and telecommunication systems.

1.1.2 The key issues are identified in:

a) the service definitions by defining essential, emergency and non-important servicesb) the power supply systems and capacity by specifications for emergency supplyc) cables and penetratorsd) documentation requirements.

1.1.3 Specific references to other relevant standards are given.

1.1.4 Design criteria for electrical penetrators are outlined. Philosophy on earthing is specified, in that hullreturn is not allowed.



1.2.2 Some testing is included in this section. For further requirements for testing, see Sec.1 [9].

1.2.3 Recognised production standards include those provided by the International Electro technicalCommission (IEC).

1.2.4 This section bears impact on Sec.3, Sec.6, Sec.7 and Sec.8.

1.3 DocumentationFor electrical systems the following shall be documented:

— Single line distribution system diagrams for the whole installation. The diagrams shall give informationon full load, cable types and cross sections, and make, type and rating of fuse- and switchgear for alldistribution circuits.

— Calculations on load balance, including emergency consumption and battery capacities.— Complete multi-wire diagrams, preferably key diagrams, of control and alarm circuits for all motors or

other consumers.— Plans showing arrangements of batteries with information about their make, type and capacity.— Plans showing arrangement and single line diagrams of the communication system.— Complete list of components and documentation on any tests carried out on all electrical equipment to be

permanently installed within the chamber and the bell.

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1.4 Codes and standardsThe following codes and standards are applicable:

a) DNV GL offshore standard DNVGL-OS-D201 electrical installationsb) DNV GL offshore standard DNVGL-OS-D202automation, safety and telecommunication systemsc) A.O.D.C.'s code of practice for the safe use of electricity underwaterd) relevant IEC equipment construction and design standards.

1.5 Service definitionsa) Essential services are herein defined as those services that need to be in continuous operation

for maintaining the diving system's functionality with regard to sustaining the safety, health andenvironment of the divers in a hyperbaric environment. This includes services required by the crewmonitoring the divers.Essential services shall be maintained for the period required by safely terminating the diving operation,including time for decompression of the divers.For services supporting divers in the water, all services are essential. 20 minutes is considered to bethe minimum time required ensuring that the divers are safely recovered in the bell or basket, or to thesurface.For services supporting divers in a bell, all services are essential. 24 hours is considered to be theminimum time required ensuring that the divers are safely recovered into the decompression chambersor to the surface.For services supporting divers in the decompression chambers, all required services are essential. Thenormal decompression schedule is considered to be the minimum time required ensuring that the diversare safely brought to the surface.

b) Emergency services are herein defined as those services that are essential for safety in an emergencycondition. Examples of equipment and systems for emergency services include:

i) condition monitoring of emergency batteriesii) emergency lightingiii) emergency communicationiv) emergency life support systemsv) emergency heating systemsvi) emergency handling of the bell(s)/basket(s)/diver(s) (if electrical)vii) alarm systems for the above emergency services.

For services supporting divers in the water, all the above services may be considered emergency servicesand 20 minutes is considered to be the minimum time required to ensure that the divers are safelyrecovered in the bell or basket or to the surface.For services supporting divers in a bell, all the above services may be considered emergency servicesand 24 hours is considered to be the minimum time required to ensure that the divers are safelyrecovered in the decompression chambers or to the surface.For services supporting divers in the decompression chambers, with the exception of handling systems,all the above services may be considered emergency services and the capacities given in [2.4.2] apply.Services to the hyperbaric evacuation system are considered separately in accordance with the IMOguidelines given in Sec.8.

c) Non-important services are those which are not essential according to the above.

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2 System design

2.1 System voltages and distribution systems types

2.1.1 Types of distribution systemsElectrical systems with hull return shall not be applied. Electrical distribution systems shall have insulatedneutral (IT).

2.1.2 System voltagesFor installations within the inner area (see definitions under Ch.1 Sec.1 [4]), the following maximum systemvoltages are permitted:

a) The chamber:

i) For power and heating equipment: max. 250 V A.C. if protected against accidental touching orinsulation failures and fitted with a trip device as outlined in [2.3.7].

ii) For lighting, socket outlets, portable appliances and other consumers supplied by flexible cables andfor communication and instrumentation equipment: max. 30 V D.C. These systems shall be suppliedby isolating transformers.

b) The bell:

i) For all electrical equipment, voltages will be accepted up to max 30 V D.C., and shall be supplied byisolating transformers.

ii) Higher voltages than specified above may be acceptable upon special consideration, providedadditional precautions are taken in order to obtain an equivalent safety standard, e.g.: by use ofearth fault circuit breakers. (See guidance note to [2.3.7].)

Electrical circuits and equipment used in water shall be considered in each separate case and in accordancewith IMCA code of practice for the safe use of electricity underwater (see [3.2.2]). Provisions shall be madeto reduce the possible fault currents, to which a diver can be exposed, to a harmless level.

2.2 Power supply systems

2.2.1 GeneralThe electrical systems and installations supplying essential services related to the divers and or the divingoperation (as defined in [1.5.1] a)), shall be supplied from a main and an emergency or transitional source ofpower as required by [2.3.2], DNVGL-OS-D201 and by DNVGL-OS-D202.

2.2.2 Emergency supply

a) The diving system shall have a source of emergency power and an emergency power supply systemindependent of the main source of power and the main power supply system, as required by DNVGL-OS-D201 Ch.2 Sec.2 [1.1.1].

b) The emergency source of power shall be a self-contained, independent source of power. It shallimmediately supply at least those services specified as emergency consumers in [1.5.1] b). It shall beeither:

i) a generator, driven by a suitable prime moverii) an accumulator batteryiii) the ship's emergency switchboardiv) a combination of the above.

Where this source of power is a generator, it shall be started automatically upon failure of the electricalsupply from the main source and shall be automatically connected within 45 sec., thereby providingemergency services.

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Where this source of power is an accumulator battery, it shall be automatically connected to an emergencypower supply system in the event of failure of the main source of electrical power. It shall be capable ofcarrying the maximum emergency load for a time specified under A501b without excessive voltage drop,carrying the emergency electrical load without recharging while maintaining the voltage of the batterythroughout the discharge period within 12% above or below its nominal voltage.If emergency consumers must be available in the switch over period from main to emergency power, eitherfor operational reasons or to avoid malfunction of the service, a transitional power source (battery back up)for these consumers shall be provided. The capacity of this transitional power shall be minimum 30 minutes.(See SOLAS reg. II-1/43 part D para.4.)

2.3 Distribution systems

2.3.1 General, arrangementThe distribution system shall be such that, the failure of any single circuit cannot influence or set otherservices out of function for longer periods.

2.3.2 If the main power to the diving system is supplied via a distribution board, this board shall have twoseparate supply circuits from different sections of the main switchboard.

2.3.3 Control gear in the inner area shall normally not be fitted. However, special arrangement may beacceptable after consideration in each case, based on special precautions (e.g. the equipment may bepressurised with pure helium (purging) or there may be other explosion protection concepts).

2.3.4 Devices for easy disconnection of all electrical installations in the decompression chambers in anemergency situation shall be fitted. These devices shall be located on the control stand. It shall be possible todisconnect each chamber separately.

2.3.5 Fuses or circuit breakers shall not be installed within the chamber and the bell, except for emergencybattery power-supply circuits.

Guidance note:

Fuse-gear may be installed outside the bell or chamber. Installation inside may be arranged as mentioned above in [2.3.3],povided the fuse-gear isn't operable by divers


2.3.6 Insulation monitoring

a) Each insulated supply system, including the secondary side of step-down or isolating transformers (orconverters) shall be provided with an automatic insulation monitoring device, actuating switch-off andalarm by insulation faults. Alarm only may be used if a sudden switch-off of the equipment may causedanger for the divers. This insulation monitoring shall be continuous.

b) The indicator shall be located at the control stand, except that indication in the bell may be accepted forequipment in the bell.

Guidance note:

Protection against insulation failures may be achieved by double insulated apparatus or earth fault circuit breakers.


2.3.7 Electric motors placed in the inner area shall be provided with overload alarms or be inherently safe.The alarms may be initiated by over current, or by temperature detector in the motor itself. For motors in thebell, alarms in the bell may be accepted. The normal over current protections (short circuit protection) on themotors shall also be in place.

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Guidance note:

The requirement provides safety against overheating, with the possible development of toxic gasses, and or danger of flash firein oxygen enriched environments. In special cases there may be other risks involved in overheating of the motors. However, ifthe motor is considered inherently safe, the requirement for the overload alarms may be revoked. This is considered preferable incases where the number of alarms should be kept at a minimum so as to avoid stressful operating conditions and or confusion.


2.4 Capacity

2.4.1 Capacity of main source of powerAll services for normal operations are according to [1.5.1]a. defined as essential services, and shall beincluded in the services to be supplied by the main source of power as described in DNVGL-OS-D201 Ch.2Sec.2 [2].

2.4.2 Capacity of emergency source of powerAll services for emergency operations are according to A501b defined as emergency services, and shall beincluded in the services to be supplied by the emergency source of power as described in DNVGL-OS-D201Ch.2 Sec.2 [3].Also:

a) Power supplies required for the operation of life support systems and other essential services shall besufficient for the life-support duration in order to cater for safe termination of the diving operation.

b) Each compression chamber shall be provided with a main and emergency source of lighting sufficientfor the life-support time and of sufficient luminosity to allow the occupants to read gauges and operateessential systems within the chamber.

c) The emergency source of power and the emergency power distribution shall be capable of handling peakloads.

2.5 Environmental requirements

2.5.1 General.All electrical equipment and installations, including power supply arrangements, shall be constructed andinstalled to operate satisfactorily under all environmental conditions for which the diving system is designed.See DNVGL-OS-D201 Ch.2 Sec.3 [2], [3] and [4].

2.5.2 Electrical equipment within the compression chamber shall be designed for hyperbaric use, oxygen-enriched atmospheres, high humidity levels and marine application. See:

a) DNVGL-OS-D202 instrumentation and telecommunication systemsb) NFPA53M (National Fire Protection Agency) manual on fire hazards in oxygen-enriched atmospheres

1990c) A.O.D.C. 043 code of practice for the safe use of electricity underwaterd) A.O.D.C. 062 use of battery operated equipment in hyperbaric conditions.

2.5.3 All materials of submerged systems shall be such that their electrical and mechanical properties arenot influenced by water absorption.

Guidance note:

See A.O.D.C.'s code of practice for the safe use of electricity underwater, DNVGL-OS-D201 and DNVGL-OS-D202.


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2.6 Inspection and testing requirements.

2.6.1 All switchboards shall be designed, constructed and certified in accordance with the requirements givenin DNVGL-OS-D201 Ch.2 Sec.4.

2.6.2 Testing shall be carried out in accordance with the requirements given in DNVGL-OS-D201 Ch.2 Sec.10[4].

3 Equipment selection and installation

3.1 General

3.1.1 Arrangements

a) All electrical equipment and installation shall be designed and arranged in order to minimise the risk offire, explosion, electrical shock, emission of toxic gases to personnel, and galvanic action of the surfacecompression chamber or diving bell.

b) The electric power supply arrangement shall be designed to minimise the risk of electrical capacitydepletion as a result of a fault, fire or explosion, electric shock, the emission of toxic gases and galvanicaction.

3.2 Enclosures

3.2.1 Pressure resistant enclosures in the inner area or on the bell shall be designed for 1.3 times the designpressure of the diving system. Tests to be carried out with gas or water as applicable.

3.2.2 In the water, all metal enclosures shall be earthed by means of a copper earth conductor incorporatedin the supply cable, with cross-section at least of the same size as the supply conductors and not less than1 mm2. For cables having metal wire braid or armour this may alternatively be used as earth conductor,provided that the braiding cross section is sufficient.

3.3 EarthingAll pressure vessels for human occupancy (P.V.H.O. chambers and bells) shall be provided with earthingconnection devices for external main protective earth bonding.

3.4 Batteries

3.4.1 Batteries shall not be installed within the inner areas (chamber or bell).

3.4.2 Battery housings shall be provided with adequate protection in accordance with DNVGL-OS-D201 Ch.2Sec.2 [9.4], so that an accumulation of generated flammable gases is avoided.

3.5 Cables and penetrators

3.5.1 Cables

a) Cables for use in the outer area (see definition under Sec.1 [4]) shall comply with DNVGL-OS-D201 Ch.2Sec.9 [2][3] and DNVGL-OS-D201 Ch.2 Sec.10 [3].All cables shall have an earthed braiding or screen around the conductors and be equipped with aninsulating outer sheet.

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b) Cables for use in the inner area (see definition under Sec.1 d)) shall comply with the requirements givenin [3.5.1]a, with exception to the materials used. The materials shall be designed for the purpose ofbeing installed into an hyperbaric atmosphere.

c) Electrical cables in the inner area shall be halogen free and shall not give off toxic, noxious or flammablegases even when overheated. Dismantled ends of insulated conductors shall be protected with sleevesof a non-combustible material ( e.g. glass fibre weave). Ordinary ship cables with insulation of ahalogenated material (e.g. P.V.C.) shall not be accepted. Synthetic insulation materials based on P.T.F.E.(Polytetrafluoroethylene) may be accepted.

d) Flexible cables for transmission of electrical power and signals from the surface support to the bell shallbe constructed as dry-core cable (i.e. water shall not reach the insulation of the individual conductors).

e) The submerged cables shall be able to withstand an external hydrostatic pressure of 1.3 times the actualexternal pressure.

f) Unless installed in pipes, electrical cables shall be readily accessible for visual inspection.g) Tensile loads shall not be transferred to the electrical cables.

3.5.2 Electrical penetrators for pressure vessels

a) All electrical penetrators in pressure containing structures shall be purpose designed and bear amanufacturer's certificate (the terms of delivery may require a higher level of certification) and shall bearranged with separate fittings.

b) Penetrators in pressure vessels shall be of the sleeve passing hull penetration types. They shall be gasand water-tight even in the event of damage to the connecting cables.

c) Electrical penetrators shall be tested at the manufacturers as specified below in d. Tests shall be madebetween each conductor and screen and tests shall be carried out on penetrators from the sameproduction batch. The tests shall be carried out in the sequence they are listed. The penetrators shallshow no sign of deficiency during and after the testing.

d) Tests to be carried out include:

— a voltage test, by applying 1 kV plus twice the design voltage for 1 minute between each conductorand screen separately

— a hydrostatic test to a pressure of twice the design pressure, repeated 5 times— a gas leakage test with the cables cut and open (testing with air to twice the design pressure or with

helium to 1.5 times the design pressure.)— an insulation test to 5 Megaohms at the design pressure, applying saltwater.

3.6 Lighting, inner areaProtection against possible bursting of electrical bulbs shall be in place.

4 Communication

4.1 GeneralCommunications systems shall comply the relevant requirements given in DNVGL-OS-D202 instrumentationand telecommunication systems.

4.2 Visual observation of divers

4.2.1 Visual observation of divers in each compartment shall be possible.

4.2.2 For saturation diving systems, suitable means (e.g. TV) shall be arranged for visual observation of thedivers in the bells from the control stand for the bells and for the divers in the chamber compartments at thecontrol stand for the chambers.

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4.3 Voice communication systems

4.3.1 Communication systems shall be arranged for direct voice communication between the control standand:

a) divers in the waterb) divers in the bellc) each compartmentd) other control standse) the bridge (operational command centre).

4.3.2 Alternative means of communication with the divers in the chamber compartments and the divers inthe bell shall be available in an emergency.

4.3.3 Diving systems intended for use of helium shall be provided with helium unscramblers. The soundquality shall be of such a level that the breathing pattern of the diver in water can be easily recognised.The control stand for the bell shall be provided with equipment for audio-recording of all communicationswith the divers in the bell and in the water.

4.3.4 The bell shall be fitted with a self-contained emergency through-water communication system.

4.3.5 A diving bell shall have an emergency-locating device, preferably with a frequency of 37.5 kHz,designed to assist personnel on the surface in establishing and maintaining contact with the submergeddiving bell if the umbilical to the surface is severed. This is in accordance with the IMO code of safety fordiving systems, 1995 (resolution A.831(19)). The device includes the following components:1. Transponder1.1 The transponder should be provided with a pressure housing capable of operating to a depth of atleast dmax containing batteries and equipped with salt-water activation contacts. The batteries should be ofthe readily available alkaline type and, if possible, be interchangeable with those of the diver and surfaceinterrogator or receiver.1.2 The transponder should be designed to operate with the following characteristics:

Table 1

Common emergency reply frequency 37.5 kHz

Individual interrogation frequencies:

- channel A

- channel B

38.5 +/-0.05 kHz

39.5 +/-0.05 kHz

Receiver sensitivity +15 dB referred to 1 μ bar

Minimum interrogation pulse width 4 ms

Turnaround delay 125.7 +/-0.2 ms

Reply frequency 37.5 +/-0.05 kHz

Maximum interrogation rates:

— more than 20% of battery life remaining— less than 20% of battery life remaining

once per second

once per 2 seconds

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Minimum transponder output power 85dB referred to 1 μ bar at 1 m

Minimum transducer polar diagram - 6 dB at +/-135° solid angle, centred on thetransponder vertical axis and transmitting towardthe surface

Minimum listening life in water 10 weeks

Minimum battery life replying at 85 dB 5 days

2. Strobe light2.1 The strobe light on the bell shall have a batterycapacity sufficient for 24 hours duration.2. Diver-held interrogator or receiver2.1 The interrogator or receiver should be provided with a pressure housing capable of operating to a depthof at least dmax with pistol grip and compass. The front end should contain the directional hydrophone arrayand the rear end the 3 digit LED display readout calibrated in metres. Controls should be provided for on andoff receiver gain and channel selection. The battery pack should be of the readily available alkaline type and,if possible, be interchangeable with that of the interrogator and transponder.2.2 The interrogator or receiver should be designed to operate with the following characteristics:

Table 2

Common emergency reply frequency 37.5 kHz

Individual interrogation frequencies:

- channel A

- channel B

38.5 kHz

39.5 kHz

Minimum transmitter output power 85 dB referred to 1 μ bar at 1m

Transmit pulse 4 ms

Directivity +/-15°

Capability to zero range on transponder

Maximum detectable range More than 500 m

4.3.6 In addition to the communication systems referred to above, a standard bell emergencycommunication tapping code should be adopted as given below for use between persons in the bell andrescue divers.A copy of this tapping code should be displayed inside and outside the bell and also in the dive control room.

Table 3 Bell emergency communication tapping code

Tapping code Situation

3.3.3 Communication opening procedure (inside and outside)

1 Yes or affirmative or agreed

3 No or negative or disagreed

2.2 Repeat please

2 Stop

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Tapping code Situation

5 Have you got a seal?

6 Stand by to be pulled up

1.2.1.2 Get ready for through water transfer (open your hatch)

2.3.2.3 You will not release your ballast

4.4 Do release your ballast in 30 minutes from now

1.2.3 Do increase your pressure

3.3.3. Communication closing procedure (inside and outside)

5 Instrumentation

5.1 GeneralIn general, instrumentation shall comply with the relevant requirements in DNVGL-OS-D202.

5.2 Control stands

5.2.1 In the design of control rooms, attention shall be given to ergonomic matters such as communicationand a systematic arrangement of equipment, according to a documented traffic flow chart. Further, it shouldbe ensured that noise or other disturbance when working does not occur (see guidance note to Sec.3[6.4.1]).

5.2.2 Indication and operation of all vital life support conditions to and from the chamber(s) and the bell(s)shall be arranged at a single control stand or divided between suitably located control stands. The controlstands shall be equipped for easy operation and control of the diving system. There shall be schematicindication of gas flow lines. For saturation diving systems the control stand for the bell shall be separatedfrom other control stands.

5.2.3 The control stands shall have indicators showing continuously:

a) the pressure in the gas containers connectedb) the pressure after all pressure reducersc) the pressure in each chamber compartmentd) the pressure externally and internally of the bell.

Pressure indicators on the control stand for the bell and compartments shall be arranged for a possiblecomparison between each other or with a permanently installed master indicator. If cross-connections areincorporated, these shall be arranged in such a way as to give the operators an indication when cross-connection is being conducted.Instrumentation for pressure measuring for bell and compartments shall have an accuracy of +/-0.3% of fullscale. In addition pressure indicators for the chambers shall facilitate depth measurements with an accuracyof +/-0.25 msw. in the depth range from 30 msw. to 0. For other instrumentation for pressure measuring,+/-1% of full scale.

5.2.4 The control stands shall have a system for continuous indication of:

a) oxygen content in each compartment individuallyb) oxygen content in bell for saturation diving systems

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c) oxygen content in the supply to the:

i) umbilicalii) compartmentsiii) masks in compartments.

The monitoring systems shall be fitted with audible and visual high and low level alarm.

5.2.5 Permanent provisions for calibration of and comparison between oxygen analysing instruments shall bearranged on the control stand.

5.2.6 There shall be a system for continuous monitoring of oxygen content in supply to the bell's umbilicaland masks in the bell. The monitoring systems shall be fitted with audible and visual high and low levelalarm. There shall be an audio-visual gas flow indicator in the oxygen supply to the chambers.

5.2.7 The control stands shall have a system for regular indication of:

a) carbon dioxide content in each compartment individuallyb) carbon dioxide content in the bell for saturation diving systems.

5.2.8 There shall be systems for indication of temperature and humidity in the inner area. For saturationdiving systems, temperature and humidity indicators for the living compartments shall be located at thecontrol stand.

5.2.9 Alarms for abnormal conditions are required at the control stand, if automatic environmental controlsystems are arranged for regulation of gas composition, pressure and temperature in the inner area.

5.2.10 It shall be possible to carry out work and to communicate effectively in the control room even if thereis no normal breathable atmosphere in the room. Release of dangerous quantities or mixtures of gas fromchamber or gas plant shall never take place in the control room.

5.3 Pressure indicators in bell and chambers.

5.3.1 The bell shall be fitted with indicators visible to the divers inside, showing:

a) external pressureb) internal pressurec) pressure of gas stored on the bell.

5.3.2 The chamber compartments shall be fitted with indicators visible to the divers inside, showing internalpressure.

5.3.3 Means shall be provided for isolating all pressure indicators without interrupting vital functions in thegas distribution system.

5.4 Oxygen analysing systems

5.4.1 Oxygen analysing systems shall have an accuracy of at least +/-0.015 bar partial pressure oxygen.

5.4.2 The bell and the living compartments shall have separate oxygen analysers inside.

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5.5 Carbon dioxide analysing systems

5.5.1 Carbon dioxide analysing systems shall have an accuracy of +/-0.001 bar partial pressure.

5.5.2 Carbon dioxide gas for calibration shall be available.

5.5.3 The bell shall have self-contained carbon dioxide analysing systems.

5.6 Other gases

5.6.1 The instrumentation for systems intended for other gases than air or helium and oxygen mixes shall beconsidered in each case.

Guidance note:

Operations in connection with exploration of oil, may require instrumentation for the analysis of hydrocarbon gases and H2S.


5.6.2 Calibration gases shall be available for each relevant gas mix.

5.7 ContaminantsFor DSV-SAT diving systems, a system for sampling and analysing of trace contaminants shall be arranged.Analysing by test tubes may be acceptable.

5.8 Automatic environmental control systems

5.8.1 The following requirements apply when systems for automatic regulation of gas composition, pressureand temperature in the inner area are installed.

5.8.2 The design principles given in DNVGL-OS-D202 apply on a general basis.

5.8.3 The most probable failure in the systems shall result in the least critical of any possible new conditions(fail to safety).

5.8.4 Automatic control systems shall keep process variables within the limits specified during normalworking conditions and the alarm systems shall be activated when the limits are exceeded.

5.8.5 Alarm at the control stand is required for abnormal conditions. The alarm system is also to be activatedby failures in the alarm system such as broken connections to measuring elements. The alarm system shallbe independent of the automatic control system so that failure in one of the systems cannot inhibit operationof the other system.

5.8.6 A manual back-up system for the automatic control system is required.

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SECTION 5 FIRE PREVENTION, DETECTION AND EXTINCTION

1 General

1.1 Objective

1.1.1 The purpose of this section is to specify additional requirements for fire protection serving divingsystems. Emphasis is placed on the special needs associated with the design and manufacture of divingsystems, whereas general requirements for fire protection are given in DNVGL-OS-D301 fire protection.

1.1.2 Key issues are identified through requirements for materials, insulation and separation from adjacentspaces, sprinkler systems and extinction agents. Reductions in hazards are ensured through these issues.

1.1.3 For quantitative design parameters and functional requirements, see the relevant standards andguidelines, including DNVGL-OS-D301.


1.2.1 In addition to the basis requirements in DNVGL-OS-D301 supplementary information is found in thenational fire protection agency codes' chapters on hyperbaric systems and oxygen enriched environments.

1.2.2 Further requirements applicable to the support vessel are given in SOLAS.


1.2.4 This section bears impact on Sec.4 (build-up of static electricity, degree of protection provided byenclosure IP for equipment on chambers covered by sprinkler systems, power to alarms) and Sec.8.

1.3 DocumentationFire prevention, detection and extinction shall be documented as follows:

a) A list of all materials to be installed in the inner area, where possible with data on and or evaluation offlammability in conditions under which the materials can be used.

b) Plans and specifications of fire detection, fire alarm and fire extinction equipment for both the inner andouter area.

1.4 Control standsControl rooms for diving systems located in hazardous zone 2 shall comply with the requirements given inDNVGL-OS-A101 Ch.2 Sec.2 Arrangements.Other control stands, essential to the function of the diving system, shall be protected such that the controlsmay be maintained whilst the divers are being evacuated in the event of a fire.

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2 Fire protection

2.1 Materials

2.1.1 The use of combustible materials shall be avoided wherever possible. Combustible materials includematerials which may be brought to explode, or burn independently in the resulting gas environment,applicable to:

a) the outer area: air at a pressure of 1 barb) the inner area: air at applicable maximum pressure.

2.1.2 Structural components, furniture and knobs, paints, varnishes and adhesives applied to these, shall beof non-hazardous materials, i.e. they shall be tested in accordance with relevant parts of IMO 2010 FTP Codeor other acknowledged standard.

Guidance note:

In order to comply with [2.1.1], materials for use in inner area should be tested at an elevated pressure. Where such materials arenot available, fitting a fixed fire extinguishing system in the inner area may be considered as an alternative.


2.1.3 Materials and arrangements are wherever possible to be made so as to avoid build-up of staticelectricity and to minimise the rise of spark production due to electrical failures or combination of materials.In inner areas without electrical equipment, the furniture and floors of electrically conductor materials maybe used. For inner areas where electrical equipment is used, the materials and arrangements shall be madeso as to minimise contact with earthed metalwork.A specific electrical resistance between 107 and 1010 ohm-1 is considered to be suitable for avoiding build-upof static electricity.

3 Fire detection and alarm system

3.1 Inner areaThe inner area should be equipped with automatic fire detection and alarm system complying with IMO FSSCode. The section or loop of detectors covering the inner area should not cover other spaces.

3.2 Fault detectionProvisions shall be made for warning of faults; e.g. voltage failure, broken line, earth fault, etc. in the firealarm and detection system.

4 Fire extinguishing

4.1 Inner area

4.1.1 Each compartment in a surface compression chamber should have a suitable means of extinguishing afire in the interior which would provide rapid and efficient distribution of the extinguishing agent to any partof the chamber.(See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.6)

4.1.2 The inner area shall be equipped with a fixed, manually actuated fire extinguishing system with sucha layout as to cover the compartments. It shall be possible to actuate the extinguisher both from within thecompartments and from outside.

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4.1.3 The extinguishing agent for the inner area shall be rechargeable without depressurising, and provisionsshall be made for possible discharge of less than the total supply of extinguishing agent.

4.1.4 The extinguishing agent shall be water, unless an approved alternative exists.

4.1.5 Fixed water-mist systems for inner area shall have minimum capacity of 2 shots of 2 min. durationwith the required application rate. Response time upon activation shall follow NFPA99, maximum 3 sec.

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SECTION 6 LAUNCH AND RECOVERY SYSTEMS

1 General

1.1 Objectives

1.1.1 Launch and recovery systems shall be certified by a competent person as lifting appliances inaccordance with the procedures applicable for the issue of an ILO form 2 certificate (International LabourOrganisation) or equivalent. Operational limitations shall be stated in an appendix to the certificate.The purpose of this section is to specify additional requirements for lifting appliances serving diving systems.Emphasis is placed on the special needs associated with the design and manufacture of diving systems,whereas general requirements for lifting appliances are given in DNVGL-ST-0378 .

1.1.2 Key issues are identified through requirements for alternative recovery of divers. Further, requirementsfor interlocking of the mating system between bell and transfer compartment shows the emphasis placed onthese essential systems. As this standard allows for the use of buoyant ascent, emphasis is placed on thesecure arrangement of such systems.

1.1.3 If the maximum allowable significant wave height is to exceed 2 m, the load conditions shall be definedthrough the use of App.B.


1.2.1 This section applies to all systems. However, requirements for handling of divers baskets may bemore lenient with respect to emergency recovery, if it is possible for the surface supplied divers to ascendindependent of the divers basket.

1.2.2 For quantitative design parameters and functional requirements, see relevant standards andguidelines, including DNVGL-ST-0378.

1.2.3 Limitations are given in the rating of the handling systems with respect to a given, specified, sea-state.


1.2.5 This section has impact on the requirements for strength with respect to deck loading on the supportvessel and to the services (see Sec.4) from the support vessel.

1.3 Documentation

1.3.1 Handling systems shall be documented as a lifting appliance in accordance with the applied code orstandard. In addition, plans and supplementary documentation shall be made available as follows:

a) Plans showing the arrangement of the handling system with specifications of loads, and dimensions ofstrength members.

b) Plans showing the function of the systems, and giving particulars of the systems. The plans shall showa schematic arrangement of the hydraulic or pneumatic piping systems and specification of controls andpower supply.

c) Calculation of the design load according to [3.1].d) Calculation of necessary design load for umbilical and guide ropes.

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e) Plans and specification of structural parts, ropes, sockets, blocks, sheaves, winches, and emergencyascent arrangement for the diving bell and mating arrangement.

f) Specifications of materials and welds, and extent of non-destructive testing.g) Specifications of wire ropes and their end connections.h) Specification of safety devices (limit switches, automatic stop of operating handle, automatic locking of

winch in case of power failure, etc).i) Specification of buoyancy of the bell at dmax and correction formulas when the buoyancy is measured at

the surface.j) Plans and specifications for systems used for emergency ascent and retrieval of the bell.k) Information on specification of working weight, displacement and stability of the bell, with all hydrostatic

properties accounted for.

2 Design principles

2.1 Function

2.1.1 The normal handling system shall be designed for a safe, smooth and easily controllable transportationof the bell in the design sea-state.The lowering of bells is, under normal conditions, to be controlled by the drive system for the winches, andnot by mechanical brakes.Bell and guide-wire winches used for dry transfer into a habitat shall include a heave compensation andconstant tension system.

Guidance note:

Care should be taken when designing handling systems with heave compensation and constant tension systems incorporated, asthe added systems often contribute to the increase in the stiffness of the overall system.


2.1.2 Manoeuvring systems shall be arranged for automatic stop when the operating handle is not operated(dead man’s handle).

2.1.3 Hoisting systems shall be fitted with a mechanical brake, which shall be engaged automatically whenthe hoisting motor stops. In the event of failure of the automatic brake a secondary means shall be providedto prevent the load from falling. This may be manual in operation and should be simple in design.

2.1.4 The handling system shall be designed so that the systems are locked in place if the energy supplyfails or is switched off.

2.1.5 If the hoisting rope can enter the drum with an angle exceeding 2° from the right angle to the drumaxis (the fleet angle), a spooling arrangement shall be fitted. The rope handling system shall not permitropes to squeeze in between, or introduce permanent deformation to ropes in underlying layers on the drum.

2.1.6 The hoisting system shall be equipped with a device which stops the bell at its lowermost anduppermost positions. Travelling cranes and trolleys shall be equipped with mechanical stops at their endpositions. The system shall be equipped with limit switches preventing the handling of the bell, wet bell orbasket outside of the handling area.

2.1.7 Precautions shall be taken to avoid exceeding the design load in any part of the handling systemincluding hoisting ropes and umbilical due to:

a) large capacity of the power unitb) motions of the supporting vessel when the bell or weights are caught or held by suction to the sea floor

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c) failure on umbilical winch during launching of bell.

2.1.8 Structural members of the handling system might be subjected to forces imposed by separate unitsof a power system. (e.g. A-frame tilted by hydraulic actuator on each leg.) The structural members aretherefore either to be strong enough to sustain the resulting forces when one of the power units fails, orthe power units shall be synchronised and an automatic alarm and stop system shall be activated when thesynchronising is out of set limits.

2.1.9 A locking arrangement shall be fitted to the mating system between the bell and the transfercompartment in accordance with the requirements given in Sec.2 [2.3.4] and [2.3.5].

2.1.10 Where direct visual monitoring of the winch drums from the winch control station is not practical, TVmonitoring shall be fitted.

2.1.11 Primary and emergency lighting in all critical handling areas shall be provided.

2.2 Alternative recovery

2.2.1 There shall be at least one normal system and two independent emergency systems for recovery ofthe divers with return to the chambers. The alternative systems shall comply with the same requirements forload strength as the main system.One of the emergency systems shall be independent of the hoisting and guide ropes, as well as the umbilical.

Guidance note:

The requirement for an emergency recovery system independent of the hoisting ropes, guide ropes and umbilical is a reminderof the fatal incidents where all these regular means of lifting the bell were severed due to snagging by anchor wires or otherobstructions. More recent systems are fitted with two bells, enabling emergency recovery by wet transfer if necessary.


a) One emergency system may be made for recovery by aid of the normal hoisting or guide rope(s) orumbilical. This system shall be independently powered from the normal system, and shall incorporate alltransportation necessary to mate the bell to the transfer chamber.

b) One system shall also provide an arrangement for stopping the bell from falling or descending, in theevent of failure in the primary lifting wire.

c) The other emergency system may consist of an arrangement on the bell that permits the divers inside toactivate a buoyant ascent of the bell, (see [2.3.1]) and shall incorporate all transportation necessary tomate the bell to the transfer chamber.

d) Alternatively, the diving system may be equipped with a separate handling system and a second bell orsubmersible. Provisions shall be available for recovery of the divers to the chambers.

2.2.2 Guide wire equipment may, in addition to ensuring controlled movements of the bell in the water,function as an alternative handling facility.

2.3 Emergency arrangements

2.3.1 Bells equipped for buoyant emergency ascent shall be specially considered. They shall be fitted withemergency release of hoisting rope(s), guide wires, umbilical and ascent system, that shall be activated insequence from inside the bell.

Guidance note:

Although this standard allows buoyant ascent as a means of emergency retrieval, it should be chosen only as a last resort when allalternatives have been considered and abandoned.


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2.3.2 Release mechanisms for hoisting rope, guide wires, umbilical and ascent system shall be so designedthat two separate operations shall be necessary to activate them. If hydraulic or pneumatic actuationsystems are used, possible penetration of helium into the systems shall be taken into account.Primary strength members shall be designed for a load not less than 3 times the expected maximum loadduring operation. Secondary strength members such as securing mechanisms shall be so designed that theycannot activate the release system in the event of their failing.

2.3.3 Bells equipped for emergency ascent shall have positive buoyancy without ballast of minimum 3% ofthe displacement with working weight (the trunk filled with water) at maximum depth.

2.3.4 The bell shall have means enabling it to be located when submerged, and in the case of a buoyant bellalso at the surface (see Sec.4 [4.3.5]).

2.4 Power

2.4.1 The bell hoisting powersystem shall be designed and tested to lift a load of 1.25 times the workingweight.

2.4.2 The power of horizontal transportation systems shall be designed and tested for safe handling at listand trim as specified in Table 1.

2.4.3 The strength of the mechanical brake for the bell hoisting system shall be based on holding of thedesign load. After the static test, however, the brake may be adjusted to the working weight of the bell plus40%.

2.5 Umbilical

2.5.1 The length of the umbilical if separated from the hoisting rope is at least to allow an excursion of thebell to:

a) dmax plus 5%, orb) actual bottom depth plus 5%.

2.5.2 The termination points, where the umbilical enters connectors and penetrators, shall not be subjectedto significant loads or flexing.

2.5.3 The ultimate tensile strength of the umbilical shall not be less than twice the maximum load expectedduring normal and emergency operations.The design load of the umbilical shall be sufficient for the maximum loads expected during normal operation.

3 Strength

3.1 Design loads

3.1.1 If the handling system is designed for operation in sea-states with significant wave heights (seedefinitions in Ch.1 Sec.1 [2.3]) not exceeding 2 metres, the design load may be taken as the load resultingfrom the following:

a) 2 times the working weight in air of bell and attachable members,

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b) weight of structural members of the handling system multiplied by a factor of 1.3 in the vertical directionand 0.3 in the horizontal direction,

c) list and trim during operation as given in Table 1,d) list and trim in locked position as given in Sec.1 [7.1].

3.1.2 Alternatively to [3.1.1], or for sea-states with significant wave heights exceeding 2 metres, the designload shall be taken as the largest most probable, resultant load over 24 hours in the operational design sea-state due to the following:

a) working weight of bell and structural members of the handling system,b) dynamical amplification due to list, trim and motion of the vessel,c) operation and response of the handling system,d) hydrodynamic forces,e) jerks in the hoisting ropes and impact on the system.

3.1.3 The working weight of the bell shall be taken as the maximum weight of the fully equipped bell,including each fully equipped diver of 150 kg. The load from this weight applies to:

a) handling in airb) handling submerged, combining the maximum negative buoyancy of the wire rope, umbilical and bell at

maximum operating depth.

3.1.4 In locked positions on a vessel, the handling system shall have a structural strength at least sufficientfor the environmental conditions described in Sec.1. In addition to the motions and accelerations in theoperational design sea-state, the minimum inclinations given in Table 1 shall be taken into account:

Table 1 Permanent inclinations

Vessel type Permanent list Permanent trim

Ship 5° 2°

Semi-submersible 3° 3°

3.1.5 Dynamic loads due to start, stop, or a slack wire rope followed by a jerk, and hydrodynamic loads shallbe determined. This may be done as stated in App.B.

3.2 Dimensions

3.2.1 The minimum safety factor for steel wire ropes shall be 4 compared to design load defined in [3.1].Minimum safety factor for synthetic fibre wire ropes shall be 5 compared to design load defined in [3.1].

3.2.2 Blocks, sheaves, shackles etc. shall comply with recognised national codes. Drums and pulleydiameters shall correspond to the type of rope. For steel wire ropes this diameter shall not be taken lessthan specified by the rope manufacturer, and normally not less than 18 times the rope diameter. In the caseof cross hauling, such equipment shall fulfil the same requirements for strength as the rest of the handlingsystem.

3.2.3 Structural members shall be fabricated from certified materials and shall be designed with safetyagainst:

a) excessive yieldingb) buckling

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c) fatigue fracture.

in accordance with technical requirements in DNVGL-ST-0378 or equivalent accepted standards. Safetyfactors at design load shall be taken as specified for case 1 (safety against yield: 1.5) in this reference.

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SECTION 7 PIPES, HOSES, VALVES, FITTINGS, COMPRESSORS,FILTERS AND UMBILICALS

1 General

1.1 Objectives

1.1.1 The purpose of this section is to specify additional requirements for pipes, hoses, valves and fittingsserving diving systems. Emphasis is placed on the special needs associated with the design and manufactureof diving systems, whereas general requirements for such systems are given in DNVGL-RU-SHIP Pt.4 Ch.6.

1.1.2 Key issues include the requirements for oxygen systems and to the limited use of hoses except hosesused in umbilicals.

1.1.3 This section does not cover general requirements given in manufacturing codes and standards forparticular components, such as API codes for hoses etc.


1.2.1 This section applies to all systems essential for the safe operation of the diving system.

1.2.2 Manufacturing standards applicable to individual components shall be supplementary to this standard.

1.2.3 Testing after completion is included here and in Sec.1, but testing during manufacture shall be inaccordance with applicable manufacturing codes for the particular component.

1.2.4 This section has impact on Sec.2, Sec.3, Sec.5, Sec.6 and Sec.8.

1.3 Documentation

1.3.1 Pipes, hoses, valves, fittings, compressors and umbilicals shall be documented as follows:

Flexible hoses Plans and specifications showing suitability of the hose in relation to its intended use.

For information, documentation of tests which have been carried out, as required.

Umbilical Plans and specifications giving particulars of conductors, minimum breaking load and minimumdiameter of pulley and drums.

For information, specification of max. design loads, elastic properties and weight per unitlength.

1.3.2 Documentation of tests verifying the properties listed above and as required by [8].

1.4 Materials

1.4.1 Materials used in the breathing gas system shall not produce noxious, toxic or flammable products.

1.4.2 Precautions shall be taken to avoid galvanic corrosion.

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1.4.3 Non-metallic materials retaining pressurised gas shall be considered for gas-permeability.

1.5 ProtectionPiping systems shall be well protected against mechanical damage.

2 Components and hoses for oxygen services

2.1 General

2.1.1 All components used in oxygen system shall be designed and oxygen shock tested based on EN ISO10297 (internal diameter of the test equipment shall be in line with the internal diameter of the test object)or other another acceptable international standard.

2.1.2 The minimum acceptable cleanliness level for components used in oxygen systems shall be ASTM LevelB (33 mg/m2) for nonvolatile residue (see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6).

2.1.3 The metallic materials used in oxygen system shall be copper, copper alloys with copper content above55% and austenitic steels with chromium-nickel content above 22%.

2.1.4 The nonmetallic materials used in oxygen systems shall be oxygen shock tested for the applicablepressure range acc. EN ISO 15001.

2.1.5 Shut of valves shall be of the types which need several turns to close. On chamber penetrators, ballvalves may be accepted for emergency use only.

2.1.6 Pressure gauges in oxygen systems shall be designed and cleaned in accordance with EN 837-1.

2.1.7 Flexible metallic hoses made of austenitic steels with chromium-nickel content above 22% can beused for oxygen systems needs to be type approved. The oxygen shock test can be waived.

2.1.8 Flexible synthetic hoses can be used in systems with maximum pressure of 40 bar.Guidance note:

The material of the inner liner of the hose should be oxygen shock tested (as required in [2.1.4]) to the applicable workingpressure of 40 bar. The length of the flexible hose installed in the system may be longer than the length of the tested hose.


2.1.9 If a lubricant is necessary to permit assembly operations or the functioning of a component, it shallbe selected from lubricants that have been found acceptable for use with oxygen and breathing gases forapplicable pressure range.

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3 Pipes and hoses

3.1 General

3.1.1 Piping systems shall comply with the technical requirements in DNVGL-RU-SHIP Pt.4 Ch.6.

3.1.2 Welding of joints shall be carried out by qualified welders using approved welding procedures andwelding consumables. Technical requirements are given in DNVGL-RU-SHIP Pt.2 Ch.3.

3.1.3 The following requirements given in DNVGL-RU-SHIP Pt.4 Ch.6, shall be followed:

a) bending and welding proceduresb) welding joint particularsc) preheatingd) heat treatment after welding and forminge) non-destructive testing and production weld testingf) bracing of copper and copper alloys.

3.1.4 Hydrostatic testing shall be in accordance with the technical requirements and as for correspondingpipe class in breathing gas systems pertaining to class I piping systems.

3.2 Hoses

3.2.1 In addition to umbilicals, short lengths (up to 2 m) of flexible hose may be used when necessaryto admit relative movements between machinery and fixed piping systems. For assemblies incorporatingspecially approved hoses and securing arrangements, lengths up to 5m may be permitted if fixed piping isnot practicable. In such cases the securing arrangements shall be in place at 1m intervals of the length of thehose.In addition to the couplings, the hoses shall be secured in such a way as to prevent the hose from whiplashing in the event that the coupling fails. When applicable, couplings shall incorporate bends so that kinksin the hoses are avoided.

3.2.2 Flexible hoses shall not replace fixed piping.

3.2.3 Flexible hoses with couplings shall be certified.

3.2.4 The bursting pressure of synthetic hoses shall be at least:

a) for hoses for fluids: 4 times the maximum working pressureb) for hoses for gases: 5 times the maximum working pressure.

3.2.5 Hot water hoses shall be designed for conveyance of fluids of temperatures not less than 100°C

3.2.6 Each hose for use in umbilical shall be pressure tested to 1.5 times the design pressure before fittingin the umbilical. After hose end fittings have been mounted, a gas leakage test to design pressure shall beperformed.

3.2.7 Flexible metallic hoses shall comply with DNVGL-CP-0183. These types of hoses shall not be installedin systems subject to excessive vibrations or movements.

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3.2.8 Flexible synthetic hoses shall comply with DNVGL-CP-0184. In addition to the testing required inDNVGL-CP-184 the requirements in [1.4.3] and [2.2.4] applies. The internal oil resistance test may beomitted for hoses intended for gas and water only.

4 Valves and pressure regulators

4.1 Valve design

4.1.1 Pressure ratings for valves shall be in accordance with a recognised national standard.

4.1.2 Design and arrangement of valves shall be such that open and closed positions are clearly indicated.

4.1.3 Valves shall normally be closed by clockwise rotation.

4.1.4 Pressure regulators shall have more than one full rotation from fully closed to fully opened position.

5 Fittings and pipe connections

5.1 Detachable connections

5.1.1 Bite and compression type couplings and couplings with brazing, flared fittings, welding cones andflange connections are only allowed for piping up to 25 mm (1") and shall be designed according to arecognised standard.

6 Compressors

6.1 General

6.1.1 Compressors shall be certified.

6.1.2 Compressors shall be equipped with all the accessories and instrumentation which are necessary foreffective and dependable operation.

6.1.3 Compressors shall be designed for the gas types and pressure rating as specified by the operation andso designed that the gas is protected against contamination by lubricants.

6.1.4 Suitable protection shall be provided around moving parts, and the safety relief valves shall exhaust toa safe place.

7 Purification and filter systems

7.1 General

7.1.1 Purification and filter systems shall be certified.

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7.1.2 The content of contaminants in the breathing gas after the filter system shall not exceed theacceptance criteria given in EN 12021 or equivalent standards. National requirements remain unaffectedhereby.

7.1.3 Where breathing gas is supplied directly from running compressors, an automatic shut off devicefor the compressor shall be installed to shut it down when the purification/filter system have reached anunacceptable level of contamination.

7.1.4 Filter housings, casings, breathing gas receivers and other parts subject to pressure shall behydrostatically tested in accordance with national and international design codes.

7.1.5 Additional requirements to external environment in terms of toxic H2S and hydro carbon gas (seeDNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [1.9]).

8 Umbilicals

8.1 GeneralUmbilicals shall be designed, tested and certified in accordance with the most recent edition of one of thefollowing codes:

a) ISO 13628-5 petroleum and natural gas industries, design and operation of subsea production systems,part 5: subsea control umbilicals

b) API specification 17E specification for subsea production control umbilicals.

8.2 HosesHoses for umbilicals shall comply with the requirements given in [2.1]. Hoses intended for operation witha larger external pressure than the internal pressure, shall be able to withstand 1.5 times this pressuredifference without collapsing or shall be able to collapse without signs of permanent deformation.

8.3 Electrical cables

8.3.1 Electrical cables for umbilicals shall comply with requirements given in Sec.4.

8.3.2 The minimum average thickness of insulating walls and temperature classes shall be in accordancewith DNVGL-OS-D201.

8.4 SheathingAny sheathing of a compact umbilical shall be of a design which avoids build-up of an inside gas pressure inthe event of a small leakage from a hose.

8.5 Strength membersThe strength members of umbilicals shall have sufficient stiffness to avoid plastic yielding of electricalconductors at design load, and shall be properly secured.

8.6 Testing of mechanical propertiesSamples of the completed umbilicals shall be tested according to a manufacturer’s test programme complyingwith relevant requirements in the design code. The test programme shall as a minimum include tensile

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testing and fatigue testing to 5000 load cycles without the umbilical showing any sign of permanentdeformation of electrical conductors and or significant permanent deformations of other parts.

8.7 Tests after completionA pressure test to the design pressure of all hoses simultaneously and verification of the specified propertiesby insulation tests of electrical conductors as well as impedance measurements of signal cables to specifiedproperties shall be carried out.

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SECTION 8 HYPERBARIC EVACUATION SYSTEMS

1 Introduction

1.1 IntroductionThese guidelines and specifications for hyperbaric evacuation systems have been developed with a viewto promoting the safety of all divers in saturation and achieving a standard of safety for divers whichcorresponds, so far as is practicable, to that provided for other seagoing personnel, and which will satisfyCh.3 of the code of safety for diving systems (resolution A.536(13), as amended by resolution A.583(14)).

1.2 Objectives

1.2.1 The purpose of this section is to outline general requirements for hyperbaric evacuation systemsserving diving systems. Emphasis is placed on the special needs associated with the design and manufactureof such systems, including requirements given by IMO. Specific requirements for pressure vessels, lifesupport systems etc. are given in each applicable chapter preceding this.

1.2.2 Key issues are identified by specifically adding to the IMO text in relation to self-propelled hyperbaricevacuation lifeboats, equipment for connection to support and rescue vessels and launch and recoverysystems.


1.3.1 SOLAS requirements shall be applied as far as practicably possible. This is particularly relevant to thelaunch and recovery systems.

1.3.2 These requirements may also be applicable as flag state requirements.

1.3.3 Some testing requirements are given, limited to those specified in the original IMO text. Additionaltesting may be relevant depending on the type of evacuation system installed.

1.4 DocumentationSee the relevant chapters in this offshore code for documentation requirements to the applicable equipmentand systems.For type approved lifeboats, relevant to SPHLs, particular document requirements are issued in connectionwith the type approval.

1.5 General requirements and preamble

1.5.1 The requirements in this subsection are in compliance with the IMO guidelines and specificationsfor hyperbaric evacuation systems, resolution A.692(17), in the following referred to as the IMOguidelines. Much of the text in this Ch.9 is IMO text. If any parts of the rules are subject to discussion ormisunderstanding, the IMO text shall prevail.

1.5.2 Hyperbaric evacuation units that are permanently connected to a certified diving system will, asa minimum, be regarded as deck decompression chambers and shall be certified as such. (See Sec.2).However, the minimum size requirements given in this standard shall be considered in each case.

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Guidance note:

For split level diving, and diving operations deeper than 200 m, two hyperbaric evacuation systems may be required to cover thevarious pressure levels.


1.6 Hyperbaric evacuation methodsIt is recognised that there are various methods available for evacuating divers in an emergency and that thesuitability of the various options for a safe hyperbaric evacuation depends on a number of factors includingthe geographical area of operation, environmental conditions, and any available offshore or onshore medicaland support facilities.Options available to diving contractors will include:

1) hyperbaric self-propelled lifeboats2) towable hyperbaric evacuation units3) hyperbaric evacuation units which may or may not be towable suitable for offloading on to an attendant

vessel4) transfer of the diving bell to another facility5) transfer of the divers from one diving bell to another when in the water and under pressure6) negatively buoyant unit with inherent reserves of buoyancy, stability and life support capable of returning

to the surface to await independent recovery.

The Guidelines and Specifications do not therefore attempt to specify which particular type of hyperbaricevacuation system should be employed and recommend that clients and diving contractors examine andidentify the option most suited for the area and type of operation in which they are engaged. Considerationmay have to be given to the provision of separate evacuation facilities for divers in saturation at significantlydifferent depths.

1.7 Contingency planning and emergency instructionsA potentially dangerous situation can arise if a floating unit, from which saturation diving operations arebeing carried out, has to be abandoned with a diving team under pressure. While this hazard should bereduced by pre-planning, under extreme conditions consideration may have to be given to hyperbaricevacuation of the divers. The hyperbaric evacuation arrangements should be studied prior to thecommencement of the dive operation and suitable written contingency plans made. Where, in the event ofdiver evacuation, decompression would take place in another surface compression chamber the compatibilityof the mating devices should be considered.Once the hyperbaric evacuation unit has been launched, the divers and any support personnel may be in aprecarious situation where recovery into another facility may not be possible and exposure to seasicknessand accompanying dehydration will present further hazards. It is, therefore, necessary that diving contractorsensure that any such contingency plans include appropriate solutions. It should be emphasised that hasty orprecipitate action may lead to a premature evacuation situation, which could be more hazardous in the finalanalysis.In preparing the contingency plans, the various possible emergency situations should be identified takinginto consideration the geographical area of operation, the environmental conditions, the proximity of othervessels, and the availability and suitability of any onshore or offshore facilities. The facilities for rescue,recovery and subsequent medical treatment of divers evacuated in such circumstances should be consideredas part of the contingency plan. In the case of unattended hyperbaric evacuation units, considerationshould be given to providing equipment to transfer the towline to an attendant vessel before launch of theevacuation unit. Such an arrangement would enable the unit to be towed clear immediately after launching.Copies of contingency plans should be available on board the parent vessel, ashore and in the hyperbaricevacuation unit.

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1.8 PurposeThe purpose of these guidelines and specifications is to recommend design and construction criteria,equipment, survey standards and contingency planning for the evacuation systems referred to in Ch.3 of thecode of safety for diving systems (resolution A.536(13)).

1.9 ApplicationThe guidelines and specifications apply to new hyperbaric evacuation units which are constructed more thantwelve months after the date on which the Assembly of the International Maritime Organization adopts theseguidelines and specifications for units which can be mated to a surface compression chamber. However, anyexisting system which, complies with the provisions of these guidelines and specifications may be consideredfor endorsement of the safety equipment certificate in accordance with 4.2. (I 2502).

1.10 Definitions

1.10.1 Self-propelled hyperbaric lifeboats are in this text understood to mean hyperbaric evacuation unitsinstalled in self-propelled lifeboats operated by crew members and life support technicians located outsidethe hyperbaric environment.

1.10.2 DefinitionsFor the purpose of these guidelines and specifications the terms used have the meanings defined in thefollowing paragraphs unless expressly provided otherwise:

Table 1

Administration Means the government of the state whose flag a ship or floating structure which carriesa diving system is entitled to fly or in which the ship or floating structure is registered

Bottle Means a pressure container for the storage and transport of gases under pressure

Breathing mixture means air or any other mixture of gases used for breathing during evacuation and, ifapplicable, during decompression

Depth means The pressure, expressed in metres of seawater, to which the diver is exposed at anytime during a dive or inside a surface compression chamber or a diving bell

Diving bell Means a submersible compression chamber, including its ancillary equipment,for transfer of divers under pressure between the work location and the surfacecompression chamber, and vice versa

Diving system Means the whole plant and equipment necessary for the conduct of diving operationsusing transfer-under-pressure techniques

Hyperbaric evacuation system Means the whole plant and equipment necessary for the evacuation of divers insaturation from a surface compression chamber to a place where decompression canbe carried out. The main components of a hyperbaric evacuation system include thehyperbaric evacuation unit, handling system and life-support system.

Hyperbaric evacuation unit Means a unit whereby divers under pressure can be safely evacuated from a ship orfloating structure to a place where decompression can be carried out

Handling system Means the plant and equipment necessary for raising, lowering and transporting thehyperbaric evacuation unit from the surface compression chamber to the sea or on tothe support vessel, as the case may be

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Hazardous areas Means those locations in which an explosive gas-air mixture is continuously present,or present for long periods (zone 0), in which an explosive gas-air mixture is likely tooccur in normal operation (zone 1), in which an explosive gas-air mixture is not likelyto occur, and if it does it will only exist for a short time (zone 2)

Life-support system Means the gas supplies, breathing gas system, decompression equipment,environmental control system, heating or cooling and other equipment required toprovide a safe environment for the divers in the hyperbaric evacuation unit under allranges of pressure that they may be exposed to during evacuation and, if applicable,during the decompression stages

Mating device Means the equipment necessary for connecting and disconnecting a hyperbaricevacuation unit and a surface compression chamber

Maximum operating depth (Of the diving system) is the depth in metres of seawater equivalent to the maximumpressure for which the diving system is designed to operate

Pressure vessel Means a container capable of withstanding an internal maximum working pressuregreater than or equal to 1 bar

Compression chamber Means a pressure vessel for human occupancy with means of controlling the differentialpressure between the inside and outside of the chamber

1.11 Design and construction principles1) The design and construction of the hyperbaric evacuation system should be such that it is suitable

for the environmental conditions envisaged, account being taken of the horizontal or vertical dynamicsnatch loads that may be imposed on the system and its lifting points particularly during evacuation andrecovery.

2) The hyperbaric evacuation unit should be capable of being recovered by a single point liftingarrangement and means should be provided on the unit to permit a swimmer to hook on or connect thelifting arrangement.

Guidance note:

This standard interprets single point lifting as applicable to the lifting appliance and not the hyperbaric evacuation unit.

Further, it is interpreted to imply that only one hook-up is required to secure the load.


3) In the design of pressure vessels including accessories such as doors, hinges, door landings, closingmechanisms, penetrators and view ports, the effects of rough handling should be considered in additionto design parameters such as pressure, temperature, vibration, operating and environmental conditions.In general, piping penetrations through the chamber should have isolating valves on both sides.

4) Materials used in the construction of hyperbaric evacuation systems should be suitable for their intendeduse.

5) Component parts of a hyperbaric evacuation system should be designed, constructed and tested inaccordance with standards acceptable to the administration.

6) Components in the hyperbaric evacuation system should be so designed, constructed and arranged as topermit easy inspection, maintenance, cleaning and, where appropriate, disinfection.

7) The hyperbaric evacuation system should be provided with the necessary control equipment to ensure itssafe operation and the well-being of the divers.

8) Special arrangements and instructions should be provided externally to enable the hyperbaric evacuationunit to be recovered safely. The instructions should be located where they will be legible when thehyperbaric evacuation unit is floating.

9) Hyperbaric evacuation systems should not be located in zone 0 or zone 1; hazardous areas and high firerisk areas should be avoided as far as is reasonably practicable.

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1.12 Equipment for connection to support and rescue vessels (HEU)

1.12.1 The hyperbaric evacuation unit (HEU) shall have an arrangement for a possible connection ofumbilical to the support vessel. The umbilical connection shall enable maintenance of proper environmentalconditions in the chamber for an unlimited time, and contain aids for communication.

1.12.2 Additional or emergency life support facility shall be provided for the HEU. The owner shall ensurethat the facility is ready for use at all times during diving.

1.12.3 This may be in the form of a life support package (LSP) that shall be kept at a suitable location fromwhere it can reach the HEU within reasonable time. A contingency plan, with risk analysis if necessary, shallbe performed for verification. Compatibility of the LSP to the HEU shall be verified.

1.12.4 Procedures for use of the LSP shall be included in the contingency plan and shall be available with theLSP and inside the HEU.

1.12.5 Relevant emergency procedures shall be available in the HEU chamber, in the HEU control and withthe LSP.

1.13 Crew facilities (HEU)

1.13.1 The chamber shall be equipped with one seat and one seatbelt for each diver.

1.13.2 In case the HEU crew has to leave the HEU, it shall be possible to secure the chamber system in away that makes it possible for the divers inside to take over the control of O2 make-up and gas supply.

1.14 Hyperbaric evacuation units1) The hyperbaric evacuation unit should be designed for the rescue of all divers in the diving system at

the maximum operating depth. The compression chamber should provide a suitable environment andadequate facilities, including, where appropriate, seat belts, for the maximum number of persons forwhich the unit is designed. The seating or other arrangements provided should be designed to providean adequate degree of protection to the divers from impact collisions during launch and while the unitis afloat. Where the chamber is intended to be occupied for more than 12 h, arrangements for thecollection or discharge of human waste should be provided. Where discharge arrangements are providedthey should be fitted with suitable interlocks.

2) The means provided for access into the compression chamber should be such as to allow safe accessto or from the surface compression chambers. Interlocks should be provided to prevent the inadvertentrelease of the hyperbaric evacuation unit from the surface compression chamber while the accesstrunking is pressurised. The mating flange should be adequately protected from damage at all timesincluding during the launch and recovery stages.

3) Arrangement should be provided to enable an unconscious diver to be taken into the unit.4) Compression chamber doors should be so designed as to prevent accidental opening while pressurised.

All doors should be so designed that, where fitted, the locking mechanisms can be operated from bothsides.

5) Arrangements should be provided to allow the occupants to be observed. If view ports are provided theyshould be situated so that risk of damage is minimised.

6) Where it is intended to carry out decompression of the divers after hyperbaric evacuation in anothersurface compression chamber, then consideration should be given to the suitability of the matingarrangements on that surface compression chamber. Where necessary, a suitable adapter and clampingarrangements should be provided.

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7) A medical lock should be provided and be so designed as to prevent accidental opening while thecompression chamber is pressurised. Where necessary, interlock arrangements should be providedfor this purpose. The dimensions of the medical lock should be adequate to enable essential supplies,including CO2 scrubber canisters, to be transferred into the compression chamber, and be of suchdimensions as to minimize the loss of gas when the lock is being used.

1.15 Life-support system1) Means should be provided to maintain all the occupants in thermal balance and in a safe and breathable

atmosphere for all environmental conditions envisaged - air temperature, sea temperature and humidity- and with the maximum and minimum number of divers likely to be carried. In determining theduration and amount of life support necessary, consideration should be given to the geographical andenvironmental conditions, the O2 and gas consumption and CO2 generation under such conditions,the heat input or removal and the emergency services that may be available for the decompressionof the divers. Gas losses as a result of using toilet facilities which discharge to outside the hyperbaricevacuation unit and medical lock operation should be taken into account in determining the amountof gases required. The effects of hypothermia should be considered and the effectiveness of thearrangements provided should be established as far as is reasonable and practicable under all conditionsenvisaged. However, in no such case should the duration of the unit's autonomous life-support endurancebe less than 72 h.

2) In addition to any controls and equipment fitted externally, compression chambers should be providedwith adequate controls within for supplying and maintaining the appropriate breathing mixtures to theoccupants, at any depth down to the maximum operating depth. The persons operating the chamber,whether they are within or outside it, should be provided with adequate controls to provide life support.As far as practicable, the controls should be capable of operation without the person who operates themhaving to remove his/her seat belt.

3) Two separate distribution systems should be provided for supplying oxygen to the compression chamber.Components in the system should be suitable for oxygen service.

4) Adequate equipment should be provided and be suitably situated to maintain oxygen and carbon dioxidelevels and thermal balance within acceptable limits while the life-support equipment is operating.

5) In addition to any instrumentation necessary outside the compression chamber, suitable instrumentationshould be provided within the chamber for monitoring the partial pressures of oxygen and carbon dioxideand be capable of operation for the duration of the available life-support period.

6) Where it is intended that divers may be decompressed within the hyperbaric evacuation unit, provisionshould be made for the necessary equipment and gases, including therapeutic mixtures, to enable thedecompression process to be carried out safely

7) An adequate supply of food and water should be provided within the hyperbaric evacuation unit. Indetermining, in particular, the amount of water to be provided, consideration should be given to the areaof operation and the environmental conditions envisaged.

8) A breathing system should be provided with a sufficient number of masks for all the occupants underpressure.

9) Provision should be made external to the hyperbaric evacuation unit, and in a readily accessible place,for the connection of emergency hot or cold water and breathing therapeutic mixture. The dimensions ofthe connections provided should be as follows:

— 3/4 in. NPT (female), hot or cold water— 1/2 in. NPT (female), breathing mixture.

The connections should be clearly and permanently marked and be suitably protected.

10) In hyperbaric evacuation units designed to pass through fires, the breathing gas bottles and pipingsystems and other essential equipment should be adequately protected. In addition, thermal insulationshould be non-toxic and suitable for this purpose.

11) First-aid equipment, sickness bags, paper towels, waste disposal bags and all necessary operationalinstructions for equipment within the compression chamber should be available within the chamber, onboard the parent vessel and ashore.

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1.16 Electrical systems and arrangements1) All electrical equipment and installation, including the power supply arrangements, should be designed

for the environment in which they will be required to be operated and designed to minimize the risk ofelectrical capacity depletion as a result of a fault, fire or explosion, electric shock, the emission of toxicgases and galvanic action. Electrical equipment within the compression chamber should be designed forhyperbaric use, high humidity levels and marine application.

2) Power supplies required for the operation of life-support systems and other essential services should besufficient for the life-support duration. The battery charging arrangements should be designed to preventovercharging under normal or fault conditions. The battery storage compartment should be provided withmeans to prevent over-pressurisation and any gas released be vented to a safe place.

3) Each compression chamber should be provided with a source of lighting sufficient for the life-supporttime and of sufficient luminosity to allow the occupants to read gauges and operate essential systemswithin the chamber.

1.17 Fire protection and extinction1) Materials used in the construction and installation should so far as is possible be non-combustible and

non-toxic.2) A fire-extinguishing system should be provided in the hyperbaric evacuation unit which should be

suitable for exposure to all depths down to the maximum operating depth.3) In hyperbaric evacuation units that are designed to float and may be used to transport divers through

fires, consideration should be given, where practicable, to providing an external water spray system forcooling purposes.

4) Hyperbaric evacuation units on ships required to be provided with fire-protected lifeboats should beprovided with a similar degree of fire protection. Areas where hyperbaric evacuation systems are locatedshall be protected so that effective evacuation can take place in the event of a fire. Control stands forhyperbaric evacuation shall be protected as specified in DNVGL-RU-SHIP Pt.5 Ch10 Sec.6.

1.18 Launch and recovery systems general

1.18.1 The launching system shall comply with a recognised national code.

1.18.2 An interlock system shall be fitted to the mating system between the evacuation unit and theevacuation-tunnel with functions as stated in Sec.2 [2.4.3], [2.4.4] and Sec.6 [2.1.9].

1.19 Launch and recovery of hyperbaric evacuation unitsWhere appropriate:

1) Means should be provided for the safe and timely evacuation and recovery of the unit and dueconsideration should be given to the environmental and operating conditions and the dynamic snatchand impact loadings that may be encountered. Where appropriate, the increased loadings due to waterentrainment should be considered. Where the primary means of launching depends on the ship's mainpower supply, then a secondary and independent launching arrangement should be provided.

2) If the power to the handling system fails, brakes should be engaged automatically. The brake should beprovided with manual means of release.

3) The launching arrangements provided should be designed to ensure easy connection or disconnectionof the hyperbaric evacuation unit from the surface compression chamber and for the transportation andremoval of the unit from the ship under the same conditions of trim and list as those for the ship's othersurvival craft.

4) Where a power-actuated system is used for the connection or disconnection of the hyperbaric evacuationunit and the surface compression chamber, then a manual or stored power means of connection ordisconnection should also be provided.

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5) The means provided for release of the falls or lift wire after the unit is afloat should provide for easydisconnection, particular attention being given to units not provided with an attendant crew.

6) Where the hyperbaric evacuation unit is designed to be recovered from the sea, or from a ship ina seaway, consideration should be given to the mode of recovery. Adequate equipment to enablea safe recovery of the unit should be provided on the unit. Permanently marked clear instructionsshould be provided adjacent to the lifting equipment as to the correct method for recovery, includingthe total weight of the hyperbaric evacuation unit. Consideration should be given to the effect whichentrained water and any bilge water may have on the total weight to be lifted by the recovery vessel.Consideration should also be given to any means that can be provided for the absorption of the dynamicsnatch loads imposed during the recovery of the hyperbaric evacuation unit from the sea.

1.20 FittingsFittings shall comply with Sec.7.

1.21 Communications1) If breathing mixtures containing helium or hydrogen are used, a self-contained primary communication

system fitted with an unscrambler device should be arranged for direct two-way communication betweenthe divers and those outside the compression chamber. A secondary communication system should alsobe provided.

2) In addition to the communication system, a standard bell emergency communication tapping codeshould be provided which meets the requirements of that specified in the amendments to the code ofsafety for diving systems (resolution A.583(14)). Copies of the tapping code should be permanentlydisplayed inside and outside the hyperbaric evacuation unit.

1.22 Location systems1) Hyperbaric evacuation units designed to be waterborne should be provided with a strobe light and radar

reflector.2) Hyperbaric evacuation units designed to be placed on the sea-bed to await independent recovery should

be provided with an acoustic transponder. The transponder should be suitable for operation with a diver-held interrogator-receiver which will be retained on board the parent ship. The equipment providedshould meet the requirements specified in the amendments to the code of safety for diving systems(resolution A.583(14)).

1.23 Markings1) Dedicated hyperbaric evacuation units should be coloured orange and be provided with retro-reflective

material to assist in their location during hours of darkness.2) Each hyperbaric evacuation unit designed to be waterborne should be marked with at least three

identical signs as shown below. One of these markings should be on top of the unit and be clearly visiblefrom the air and the other two be mounted vertically on either side and as high as possible and becapable of being seen while the unit is afloat.

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3) Where applicable, the following instructions and equipment should be clearly visible and be kept readily

available while the unit is afloat:

1) towing arrangements and buoyant towline2) all external connections, particularly for the provision of emergency gas, hot/cold water and

communications3) maximum gross weight of unit in air4) lifting points5) name of the parent ship and port of registration6) emergency contact telephone, telex and facsimile numbers.

4) Warning instructions. Where appropriate, the following instructions should be permanently displayed onevery hyperbaric evacuation unit in two separate locations so as to be clearly visible while the unit isafloat:Unless specialised diving assistance is available:

1) do not touch any valves or other controls2) do not try to get occupants out3) do not connect any gas, air, water or other supplies4) do not attempt to give food, drinks or medical supplies to the occupants5) do not open any hatches.

1.24 Stability and buoyancy1) Hyperbaric evacuation units designed to float should be provided with adequate stability for all envisaged

operating and environmental conditions and be self-righting. In determining the degree of stability to beprovided, consideration should be given to the adverse effects of large righting moments on the divers.Consideration should also be given to the effect which equipment and rescue personnel, required to beplaced on the top of the system to carry out a recovery from the sea, may have on the stability of thehyperbaric evacuation unit.

2) Towing attachment points should be so situated that there is no likelihood of the hyperbaric evacuationunit being capsized as a result of the direction of the tow line. Where towing harnesses are provided theyshould be lightly clipped or secured to the unit and, so far as is possible, be free from snagging whenpulled free.

3) Hyperbaric evacuation units designed to float should have sufficient reserves of buoyancy to enable thenecessary rescue crew and equipment to be carried.

4) Where hyperbaric evacuation units are designed to be placed on board a rescue vessel, attachmentpoints should be provided on the unit to enable it to be secured to the deck.

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1.25 Self-propelled hyperbaric evacuation lifeboat

1.25.1 If self propelled hyperbaric evacuation lifeboats are required by statutory regulations or installed tocomply with operational criteria, the following requirements apply:

1.25.2 The hyperbaric evacuation lifeboat's hull, machinery, equipment, manoeuvrability and seagoingproperties shall comply with SOLAS 1974 (international convention for the safety of life at sea) and arelevant recognised national code.

Guidance note:

Lifeboats may be type approved.


1.25.3 The hyperbaric evacuation lifeboat shall be fitted with seating arrangement sufficient to carry themaximum number of divers and crew members in a sitting position.

1.25.4 The hyperbaric evacuation lifeboat shall have a sheltered area for at least 3 crew members in additionto the divers in the chamber. In this sheltered area the controls for the hyperbaric evacuation unit shall belocated.

1.25.5 The system shall be designed such that the time necessary to disconnect and launch the hyperbaricevacuation lifeboat shall not exceed 10 minutes, counted after all divers and crew members have entered thehyperbaric evacuation lifeboat and until it is free floating with the engine running.

1.25.6 The chamber shall have windows towards the sheltered part in the lifeboat.

1.25.7 The hyperbaric evacuation lifeboat shall have a self-contained support system with capacity for atleast 72 hours.

1.25.8 The hyperbaric evacuation lifeboat shall have emergency radio communication and location systemscomplying with requirements given in IMO Res. MSC 149 (77), see SOLAS reg. III/6.2.1.

1.25.9 The propulsion unit shall have sufficient power for 10 minutes running without using air from theatmosphere outside the boat. (Depending on the required level given in the safety certificate of the supportvessel, this may also be a requirement for the HEU.)

1.25.10 Masks for breathing or breathing apparatus shall be available for the crew members and life-supporttechnicians at atmospheric pressure. The masks shall be connected to air storage sufficient for 30 minutesbreathing.

1.26 Testing, surveys and drills - generalTesting of the hyperbaric evacuation system with hyperbaric evacuation unit and the handling system shall becarried out to the maximum possible extent to SOLAS requirements and to Sec.2.

1.27 Maintenance and testingThe availability of any hyperbaric evacuation system provided is dependent on the regular testing andmaintenance of the system. A planned maintenance and testing programme shall be devised with theresponsibility for carrying out the maintenance tasks being allocated to specific crew members. Maintenance

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and testing schedules shall be available for recording the execution of the tasks and the signatures of thepersons allocated the tasks. Such schedules shall be maintained on board and be available for inspection.

1.28 Surveys

1.28.1 DNV GL scopes for surveys of diving systems are given in DNVGL-RU-OU-0375.

1.28.2 1) Each hyperbaric evacuation system should be subject to:

1) an initial survey before being put into service. This should comprise a complete and thoroughexamination of the hyperbaric evacuation system, equipment, fittings, arrangements and materialsincluding functional tests which should be such as to ensure they are suitable for the intended serviceand in compliance with these guidelines and specifications

2) a survey at intervals specified by the administration but not exceeding 2 years3) an annual inspection within 3 months of each anniversary date of the survey to ensure that the

hyperbaric evacuation system, fittings, arrangements, safety equipment and other equipment remain incompliance with the applicable provisions of the guidelines and specifications and are in good workingorder.

2) Where a hyperbaric evacuation system complies with the provisions, as applicable, of the guidelines andspecifications and has been duly surveyed, it may be recorded on the supplement to the cargo ship safetyequipment certificate as providing the life-saving appliances and arrangements for divers in compression.

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APPENDIX A SELECTION OF SAFETY OBJECTIVE

1 Introduction

1.1 General principles (informative)

1.1.1 The selection of the safety objective depends on the criticality of each of the elements that have animpact on the management of risks to the diving system.

1.1.2 Certification shall direct greatest effort at those elements of the diving system where the risk is highestand whose failure or reduced performance will have the most significant impact on safety and environmentalrisks.

1.1.3 Suitable selection factors include, but are not limited to, the:

a) overall safety objectives for the diving systemb) assessment of the risks associated with the diving and the measures taken to reduce these risksc) degree of technical innovation in the diving systemd) experience of the contractors in carrying out the worke) quality management systems of the owner and it’s contractors.

1.1.4 Due to the diversity of various diving systems, their contents, their degree of innovation, thegeographic location, etc. It is not possible to give precise guidelines on how to decide what safety objective isappropriate for each particular diving system.Therefore, guidance is given as a series of questions that should be answered when deciding the appropriatesafety objective for a diving system. This list is not exhaustive and other questions should be added to thelist if appropriate for a particular diving system.

1.1.5 It is emphasised that the contribution of each element should be judged qualitatively and orquantitatively. Wherever possible quantified risk assessment data should use to provide a justifiable basis forany decisions made.

1.1.6 Depending of the stage of the project, the activities may not have taken place yet in which case thequestions can also be posed in another form, i.e. is …. planned to be?

2 Trigger questions

2.1 Overall safety objectivea) Does the safety objective address the main safety goals?b) Does the safety objective establish acceptance criteria for the level of risk acceptable to the owner?c) Is this risk (depending on the diving and its location) measured in terms of human injuries as well as

environmental, economic and political consequences?

2.2 Assessment of riska) Has a systematic review been carried out to identify and evaluate the probabilities and consequences of

failures in the diving system?b) Has this review judged the contribution of each element qualitatively and or quantitatively and used,

where possible, quantified risk assessment data to provide a justifiable basis for any decisions made?

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c) Does the extent of the review reflect the criticality of the diving system, the planned operation andprevious experience with similar diving systems?

d) Does this review identify the risk to the operation of the diving system and to the health and safety ofpersonnel associated with it or in its vicinity?

e) Has the extent of the identified risks been reduced to a level as low as reasonably practicable by meansof one or both of:

f) Reduction in the probability of failure?g) Mitigation of the consequences of failure?h) Has the result of the systematic review of the risks been measured against the owner’s safety objective?i) Has the result of this review been used in the selection of the appropriate certification activity?

2.3 Technical innovationa) Has the degree of technical innovation in the diving system been considered?b) Has it been considered that risks to the diving are likely to be greater with a high degree of technical

innovation than with a diving designed, manufactured and installed to well-known criteria in well-knownwaters?

c) Have factors been considered in the selection of the appropriate certification such as:

— Degree of difficulty in achieving technical requirements?— Knowledge of similar diving systems?— Effect of the new diving system on the area or vessel?

2.4 Contractors’ experiencea) Has the degree of risk to the diving system been considered where design, construction or installation

contractors are inexperienced?b) Has the degree of risk been considered where the contractors are experienced but not in similar work?c) Has the degree of risk been considered where the work schedule is tight?

2.5 Quality management systemsa) Have all parties involved in the diving system implemented an adequate quality management system to

ensure that gross errors in the work are limited?b) Do these parties include the:

i) ownerii) design contractoriii) construction contractorsiv) sub-contractorsv) installation contractorvi) operator (when relevant).

c) Do the factors being considered when evaluating the adequacy of the quality management systeminclude:

i) Whether or not an ISO 9000 or equivalent certified system is in place?ii) Results from external audits?iii) Results from internal audits?iv) Experience with contractors’ previous work?v) Project work force familiarity with the quality management system?

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3 Systematic review/analysis

3.1 What to do and how? (informative)

3.1.1 Submitted so called FMEAs, reveal that there appears to be a misconception of how to approach thesystematic review required in Sec.3.

3.1.2 Hazards identification and risk assessment involves a series of steps as described in DNVGL GL-OS-A101 App.B for formal safety assessment and includes: identification of the hazard, reduction of thelikelihood & reduction of the consequence. Alternative standards include ISO 17776:2000(E) that may alsogive adequate guidance.

3.1.3 The correct choice of tools, in the correct order, is paramount to a systematic review and ISO 17776,4.5 selection of structured review techniques and Annex B, describes this.

3.1.4 When the tool is chosen, it is important to report the results of the analysis in the appropriate formatfor the chosen tool:

a) It makes no sense reporting a HAZID in the format of a FMEA, or vice versa.b) The safety objectives need to be clearly defined and verifiable.c) The scope of the analysis and boundaries of the diving system shall be clearly defined.d) The actions given in the analysis when dealing with failures are critical to safety. Operating procedures

and crew familiarisation/handover procedures should be reviewed to ensure crew can adequately handlethe failure scenarios should they occur.

e) Failure modes where maintenance is listed as either detection or mitigation should be collated as a tablefor input into the planned maintenance system.

f) Is there anything else on the vessel which may impact the system? ICE class, helideck, well interventionetc.

g) It should also be shown who was involved in the preparation of the analysis.

3.1.5 A typical, but not exhaustive, list of hazards/failures includes:

a) outer or inner area fireb) releases with potential to result in firesc) explosions, and/or toxic hazardsd) loss of pressure containmente) contamination of living environmentf) loss of power to the diving systemg) failure of handling systemsh) loss of communication to/from the diving system.

3.1.6 Note that correct syntax is required to effectuate a correct order of identification and evaluation offailures.

a) A correct syntax in this case would be: failure A may lead to serious consequences therefore mitigation Xis implemented to arrive at less serious (consequences and/or probability) = risk.

b) Wrong syntax is frequently stated as: failure A will not lead to serious consequences because ofmitigation X.As this type of syntax is reversible (because of mitigation X failure A does not lead to seriousconsequence), it frequently leads to an improper view of the risk and an early termination of the analysisprocess.

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APPENDIX B DYNAMIC LOADS IN BELL HANDLING SYSTEMS

1 General

1.1 GeneralApproximate estimates of expected dynamic loads during handling of diving bell and any connected cursorfrom a vessel which is stationary and heading in the main direction of incoming waves in the design sea-stateare given in [2] and [3].The specified methods for calculation of hydrodynamic forces are limited to the cases in which the verticalmotions of the suspended bell may be taken equal to the corresponding motions of the support vessel. Theconditions permitting such assumptions are specified in [2.1.2].Other approximate or more accurate methods may be acceptable upon consideration in each case.See DNVGL-RP-C205 environmental conditions and enviromental loads.

1.2 Definitions and abbreviations

1.2.1 Parameters applied for calculation of the forces.m = mass of bell in air corresponding to its working weight including trapped water {kg}.ρ = mass density of seawater = 1030 kg/m3.V = volume of displaced water {m3}.A = cross sectional area of bell with appendices projected on a horizontal plane {m2}.Cm = coefficient for added mass (water). (For typical -diving bells with appendages such as gas

containers, bumper structure etc. the coefficient may be taken as Cm = 1.0). Above water Cm = 0.Cd = drag coefficient. (For typical diving bells with -appendages the coefficient may be taken as Cd =

1.5).a = maximum expected vertical acceleration of the bell {m/s2}.ar = maximum expected vertical relative acceleration between bell and water particles {m/s2}.v = maximum expected vertical velocity of the bell {m/s}.vr = maximum expected vertical relative velocity between bell and water particles {m/s}.

fw = reduction factor for the wave action on the bell, depending on the submerged depth z of the bell,given by:

z = submerged depth of the bell {m} when larger than hs.

hs = significant wave height {m}.Guidance note:

Significant wave height: when selecting the third of the number of waves with the highest wave height, the significantwave height is calculated as the mean of the selection.


e = 2.72fa and fv = reduction factors due to wave action (see [2.1.2]) under the heading motions of ship shaped

support vessels.k = stiffness of the handling system {N/m}.CB = block coefficient of vessel.

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Rp = horizontal distance from centre of mass (i.e. bell) to the axis of rotation, which may be takenat 0.45 L from the after perpendicular of the vessel {m}.

Aw = cross sectional area of moon pool.sr = maximum expected relative amplitude (+/-) of motion between sea surface and support

vessel in way of moon pool {m}.g = acceleration of gravity = 9.81 m/s2

d = draught of vessel at bottom of opening for moon- pool for d > hs {m}

1.2.2 Parameters applied for correction of units in empirical formulae:h1 = 1 m -1

L1 = 1 m -1

u1 = 1 m/su2 = 1 m

2 Loads on negative buoyant bell

2.1 Loads on bell clear of support vessel

2.1.1 ForcesIn a free flow field the maximum vertical hydrodynamic load Fn acting on a negative buoyant bell in thedesign sea-state may be taken as the smaller of the values obtained from the two following formulae:

Faw = force due to the combined acceleration of bell and water particles, given by:

Faw = (m – ρV)a + ρV(1 + Cm)faar {N}Fv = force due to the relative velocity between bell and water particles, given by:

Fv = 0.5 ρ A Cd(fvvr)2 {N}

Fa = force due to acceleration of bell, given by:

Fa = (m + Cm ρ V)a {N}Fw = force due to acceleration of water particles in the -deepest wave, given by:

Fw = 0.4(1 + Cm)fwρ V g {N}The parameters and principles applied for calculation of the forces are given in [2.1.2].

2.1.2 Motions of ship shaped support vesselsThe vertical motions of the bell may be taken equal to those of the support vessel when the naturaloscillating period of the handling system is less than 3 seconds, as given by:

For calculation of the forces from the formulae given in [2.1.1] the launching or retrieval velocities should beadded to v and vr.The estimation method for a and ar as well as v and vr given in the following may be used for vessels withlength between perpendiculars L {m} in the range:

50 < L < 150,

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operating in sea-states with significant wave heights hs {m}of magnitude:2 < hs < 8

The heave acceleration az of the support vessel is given by the smaller of:

or az as obtained from the rules for classification of ships.The pitch acceleration ap of the support vessel is given by:

The combined vertical acceleration from heave, pitch and roll is given by:

r = coefficient of roll= 1.0 at centreline of vessel= 1.2 at sides of vessel

The relative acceleration ar between vessel and water particles at surface is given by:

q = coefficient for position of bell.= 1.3 at stern.= 1.1 at sides amidship.= 1.0 at vessel's centreline amidship.

The vertical velocity of the vessel may be taken as:

The relative vertical velocity between vessel and water particles at surface is given by:

fa = reduction factor for vertical relative acceleration of bell due to wave action, given by:

fv = reduction factor for vertical relative velocity of bell, given by:

2.2 Hydrodynamic loads on bell in moon poolIn the flow field of a moon pool (narrow well) the maximum vertical hydrodynamic load Fm acting on anegative buoyant bell may be taken as derived from [2.1], when Cm and Cd are substituted by fm · Cm and fd· Cd respectively, where:fm = 1 + 1.9 (A / Aw)2.25

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The factors fm and fd obtained from the above apply to moon pools of constant cross section and for the ratioA/Aw < 0.8The relative accelerations ar and velocities vr refer to the flow field above the bell.When A/Aw approaches 1, the hydrodynamic load on the bell approaches the dynamic part of the bottompressure, and may be taken as:

For a moon pool at the centerline of the support vessel sr may be taken as:

where ar is obtained from [2.1.2].Symbols, see [1.2].

2.3 Impulse loads

2.3.1 Impulse loads Fi caused by sudden velocity changes in the handling system by start, stop and snatchloads in hoisting ropes may be taken as :

vi = impulse velocity {m/s} obtained from [2.3.2] or [2.3.3].Symbols defined in [1.2].

2.3.2 Impulse velocityThe impulse velocity vi during start and stop may be taken as the maximum normal transportation velocity.

2.3.3 SlackSlack hoisting rope may be expected when

|Fn| > (m – ρ V) gWhen Fn (obtained from [2.1]) is mainly wave induced and a snatch load is of short duration relative to thewave period i.e. when the natural oscillating period of the handling system is less than 3 seconds as given in[2.1.2] , then the impact velocity vi may be taken as:vi = v1 + v2 Ci

v1 = free fall velocity {m/s} in calm water

v2 = vrfv as obtained from [2.1.2] for tight hoisting ropesCi = probability coefficient obtained from the table below

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Table 1 Ci versus v1/v2

Ci

1

0

3 Loads on a positive buoyant bell (at surface)

3.1 Impulse loads

3.1.1 Impulse loads Fi caused by sudden velocity changes in the handling system by start, stop and snatchloads in hoisting ropes may be taken as follows:

Ve = volume of displaced water of the floating bellvi = impulse velocity {m/s} is taken to be as follows:

vr = from [2.1.2] {m/s}vhoist = normal transportation speed

4 Design loads

4.1 Maximum load

4.1.1 The maximum load P in the vertical direction may be taken as follows:In water:

P = (m – ρV)g + Fwhere F is the larger of Fn and Fi obtained from [2.1], [2.2] and [2.3].In air:

4.1.2 The design load in the vertical direction may be obtained from the following table.

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Table 2 Design loads

Design load

P

0.75P

Cha

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– h

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CHANGES – HISTORICThere are currently no historical changes for this document.

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DNVGL-OS-E402 Diving systems - Rules and standards - DNV

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