Electrical Area Classification

REG – 003 of 29

ELECTRICAL AREACLASSIFICATION Re v. 0

PROPRIETARY INFORMATION — For Auth oriz e d Com pany Us e O nly

1. ScopeThis document provides guidance for the classification of hazardous, onshoreprocess plant areas where there is a risk for the ignition of a flammable fuel/airmixture at atmospheric conditions. Electrical area classification allows for theproper selection and installation of equipment best suited for such environments.

The guidelines and recommendations provided herein are based on currentknowledge of industry practice and should be considered a starting point forfurther development during the Front-End Engineering Development (FEED)phase. During FEED, electrical area classification should accommodate theresults of the Environmental Impact Assessment (EIA) study, process hazardreviews, vapor dispersion studies, thermal radiation exclusion zones and noisepollution studies, as well as the latest site data.

The following conditions are excluded from the scope of this Guide:

ë Catastrophic failures1

ë Areas where the presence of flammable mist may give rise to anunpredictable risk and which would require special consideration2.

2. PurposeThe intent of this document is to set out the engineering criteria against whichthe risk of ignition of hazardous quantities and concentrations of flammable gasor vapor can be assessed. It is also the intent, to provide guidance on the designand control parameters that can be used as to reduce this risk.

3. GeneralThe electrical area classification procedure should comply with local codes andstandards at the country in which the electrical equipment is to be installed. Incase such codes and standards do not exist, conformance with the AmericanPetroleum Institute (API) Recommended Practice (RP) 500, Recommended

1 Catastrophic failure, in the context of this Guide, refers to events such as the rupture of a process vessel orthe full bore failure of a pipeline. The intent is to exclude events that have an extremely low probability ofoccurrence.2 Mists may form or be present at the same time as flammable vapors. This may affect the way flammablematerial disperses and thus, the extent of any hazardous areas. The strict application of area classification forgases and vapors may not be appropriate because the flammability characteristics of mists are not alwayspredictable. While it can be difficult to decide upon the type and extent of classified areas, the criteriaapplicable to gases and vapors will, in most cases, give a safe result. However, special consideration shouldalways be given to the ignition of flammable mists.

REG – 003 of 29



Practice for Classification of Locations for Electrical Installations at PetroleumFacilities should be considered. The use of alternative codes, e.g., BritishStandards, is acceptable if they are the general practice used by local contractors.

Unusual conditions, or the presence of hazardous materials other than thoseconsidered in API RP 500, may require modification of the practices containedtherein. The following National Fire Protection Association (NFPA) Codes maybe used as alternate source of information for electrical area classification:

ë NFPA 30, Flammable and Combustible Liquids Code.ë NFPA 70, National Electric Code.ë NFPA 497M, Classification of Gases, Vapors and Dusts for Electrical

Equipment in Hazardous (Classified) Locations.

4. Safety PrinciplesFacilities, in which flammable materials are handled or stored, should bedesigned, operated and maintained so that the releases of flammable material,and subsequent extent of classified areas, are kept to a minimum with regards tofrequency, duration and quantity.

In situations where there may be a flammable atmosphere, the following stepsshall be taken:

ë Eliminate the likelihood of a flammable atmosphere occurring aroundthe source of ignition.

ë Eliminate the source of ignition.

Where this is not possible, protective measures, process equipment, systems andprocedures should be selected and prepared so the likelihood of the coincidenceof both factors is so remote as to be acceptable. Such measures may be usedsingly if they are recognized as being highly reliable, or in combination to achievean equivalent level of safety.

5. Area ClassificationThis Guide provides a universally acceptable set of rules for the selection ofequipment to be located in areas where flammable atmospheres may occur. Themain objective of these rules is to minimize the potential for electrically inducedignition in such circumstances.

Area classification in this document is based on the guidelines provided by theAPI RP 500. However, as of 1996, the National Electric Code (NEC) has givenan alternative approach based on the work done by the International

REG – 003 of 29



Electrotechnical Commission (IEC) and Comite Europeen de NormalisationElectrotechnique (CENELEC). Either the traditional or the alternate methodmust be selected for a given hazardous (classified) location.

The alternate approach has been in use for many years in most Europeancountries and has been adopted as a standard in Belgium, France, Germany andthe United Kingdom.

API RP 500 defines electrical equipment suitable for use in Class I, Division 1and 2 locations. NEC, article 505 defines equipment suitable for use in Class I,Zone 0, 1 and 2 locations. Mixing classification methods in a single classified areais not permitted. A comparison of API’s Division and NEC’s Zone classificationsystems is shown in Table 5-1 below.

Table 5-1 — Comparison of NEC Division and Zone Classification Systems

Historical Approach Alternate Approach

Class I, Division 1 — where ignitableconcentrations of flammable gases (vapors) canexist: (a) normally during operating conditions; (b)frequently because of repair, maintenance orleakage; or (c) accidentally where the possibilityexists of a simultaneous release of ignitableconcentrations of gas (vapor) and failure ofelectrical equipment.

The Code states where ignitable concentrations offlammable gases (vapors) can exist continually orfor long periods, electrical equipment should beavoided altogether, or, intrinsically safe systemsshould be used.

Class I, Zone 0 — where ignitable concentrationsof flammable gases (vapors) can exist: (a)continually or (b) for long periods.

Class I, Zone 1 — where ignitable concentrationsof flammable gases (vapors) can exist: (a) normallyduring operating periods; (b) frequently because ofrepair, maintenance or leakage; (c) accidentallywhere the possibility exists of a simultaneousrelease of gas (vapor) and failure of electricalequipment so as to cause ignition; or (d) becausethe area is adjacent to a Zone 0 area, from whichgas (vapor) can be communicated.

Class I, Division 2 — where (a) areas containingvolatile flammable liquids or gases, where thesematerials are normally confined to closedcontainers and systems from which the materialscan escape only upon the rupture or breakdown ofcontainment or upon abnormal operation ofequipment or process; (b) ignitable concentrationsof gases (vapors) are normally prevented bypositive mechanical ventilation, but which mightbecome hazardous through failure or abnormaloperation of ventilation equipment; or (c) adjacentto Class I, Division 1 location from which ignitableconcentrations of gases (vapors) might occasionallybe communicated.

Class I, Zone 2 — where (a) ignitableconcentrations of flammable gases (vapors) are notlikely to occur during normal operations, and ifthey do occur, they will exist for only a short periodof time; (b) areas in which flammable liquids orgases are normally confined to closed containersand systems from which the materials can escapeonly upon the rupture or breakdown or uponabnormal operation of equipment or process; (c)ignitable concentrations of gases (vapors) arenormally prevented by positive mechanicalventilation, but which might become hazardousthrough failure or abnormal operation ofventilation equipment; or (d) adjacent to Class I,Division 1 location from which ignitableconcentrations of gases (vapors) might occasionallybe communicated.

REG – 003 of 29



In lieu of Group A, B, C, and D atmospheres, the alternate system establishesGroups I, IIA, IIB and IIC atmospheres. A Group IIA is equivalent to a GroupD atmosphere. Group IIB is equivalent to a Group C. Group IIC is equivalent toGroups A and B combined. These comparisons are shown in Table 5-2.

Table 5-1 — Comparison of Historic and Alternate NEC Class I Grouping Systems

Class I Content (Liquid, Gas or Vapor) Historical Approach Alternate Approach

Atmospheres containing acetylene Group A

Atmospheres containing hydrogen, fuel and combustibleprocess gases containing more than 30% hydrogen byvolume, or gases or vapors or equivalent hazard such asbutadiene, ethylene oxide, propylene oxide and acrolein.

Group B

Group IIC

Atmospheres containing ethyl ether, ethylene, or gases orvapors of equivalent hazard

Group C Group IIB

Atmospheres containing acetone, ammonia, benzene,butane, cyclopropane, ethanol, gasoline, hexane,methanol, methane, natural gas, naphtha, propane, orgases or vapors of equivalent hazard

Group D Group IIA

5.1 ObjectivesProper analysis, design and suitable operating procedures should lead to aminimal presence and/or extent of Class I, Division 1 (Zone 0 and/or Zone 1)locations. Facilities and installations should be mainly non-classified or Class I,Division 2 (Zone 2) locations.

Where release of flammable material is unavoidable, process equipment itemsshould be limited to those that give secondary grade type releases. If this is notpossible and continuous or primary sources of release are unavoidable, thereleases should be of very limited quantity and rate.

When performing electrical area classification, these principles should receive theutmost consideration. Where necessary, the design, operation and location ofprocess equipment should ensure that, even when it is operating abnormally, theamount of flammable material released into the atmosphere is minimized andtherefore, reducing the extent of the classified area.

5.2 ProcedureSince it is extremely difficult by simple examination to determine which part of afacility can be equated to the two classified area definitions (Class I, Division 1and 2); a more detailed approach is therefore necessary. Such an approach

REG – 003 of 29



involves the analysis of the basic possibility of the occurrence of an explosiveatmosphere.

The first step is to assess the likelihood of this, in accordance with Class I,Division 1 or 2 definitions. Once the likely frequency and duration of a release(and hence the grade of release), the release rate, concentration, velocity,ventilation and other factors which affect the type and/or extent of the classifiedarea have been determined, there is then a firm basis on which to determine thelikely presence of an explosive atmosphere in the surrounding areas. Thisapproach therefore requires detailed consideration to be given to each of theprocess equipment which contains a flammable material, and which could be asource of release.

Once the facility has been classified and any necessary records made, it is ofparamount importance that no modification to equipment or operatingprocedures is made without discussion with those individuals responsible for thearea classification. Unauthorized action may invalidate the area classification. It isalso necessary that all equipment affecting area classification and which has beensubject to maintenance is carefully checked during and after re-assembly toensure that the integrity of the original design, as it affects safety, has beenmaintained before it is returned to service.

Area classification should be performed by individuals who have knowledge ofthe properties of flammable materials, the process and the equipment, inconsultation as appropriate, with safety, electrical and other engineeringdiscipline personnel.

Figure A.1 on Appendix A and the following paragraphs give guidance on theprocedure for the classification of areas in which it may exist an explosiveatmosphere. It also gives guidance on the extent of Class I, Division 1 and ClassI, Division 2 areas.

5.2.1 Sources of ReleaseThe basic element for establishing area classification is the identification of thesource of release and the determination of the grade of release.

Since an explosive atmosphere can only exist if a mixture of flammable gas orvapor and air is present, it is necessary to decide if any of the flammablematerials can exist in the area of concern. Therefore, it is necessary to identifywhere a flammable atmosphere can exist inside a process plant, or where arelease of flammable materials can create a flammable atmosphere outside aprocess plant.

Each item of process equipment should be considered as a potential source ofrelease of flammable material. If the item cannot contain flammable material, it is

REG – 003 of 29



obvious that it cannot give rise to a hazardous area around it. The same willapply if the item contains a flammable material but cannot release into theatmosphere (e.g., an all welded pipeline).

If it is established that the item may release flammable material into theatmosphere, it is necessary to determine the grade of release by establishing thelikely frequency and duration of the release. It should be recognized that theopening of parts of an enclosed system (e.g., filter changing) should beconsidered as a source of release. By means of this procedure, each releaseshould be categorized as an either “continuous”, “primary” or “secondary”release type. Appendix B lists a number of sources of release examples.

Once the grade of release has been established, it is necessary to determine therelease rate and other factors that may influence the type and extent of theclassified area.

5.2.2 Type of Classified AreaThe likelihood of the presence of an explosive atmosphere and hence, the typeof classified area depends mainly on the grade of release and the ventilation3.

5.2.3 Extent of the Classified AreaTypical and specific extent of classified areas is given in API RP 500. However,the extent of a classified area is mainly affected by the following parameters,some of which are inherent to the properties of the flammable material; othersare specific to the process. For simplicity, the effect of each parameter listedbelow assumes that the other parameters remain unchanged.

5.2.3.1 Release rate of gas or vaporThe greater the release rate, the larger the extent of the classified area. Therelease rate depends itself on other parameters, namely:

ë Geometry of the source of releaseë Release velocityë Concentrationë Volatility of the flammable liquidë Liquid temperature

3 A continuous or primary grade release normally leads to a Class I, Division 1 classification, and a secondarygrade to a Class I, Division 2 classification.

REG – 003 of 29



5.2.3.2 Lower Flammability Limit (LFL)For a given release volume, the lower LFL the larger the extent of the classifiedareas.

5.2.3.3 VentilationWith increased ventilation, the extent of the classified area will be reduced.Obstacles, which hinder ventilation, may increase the extent of the classified area.Conversely, some obstacles like dikes, walls or ceilings, may limit the extent.

5.2.3.4 Relative density of the gas or vaporThe horizontal extent of the classified area at ground level will increase withincreasing relative density and, the vertical extent above the source will increasewith decreasing relative density4.

5.2.3.5 Other parametersë Climatic conditionsë Topography

5.2.4 ExamplesTypical examples on how the above mentioned parameters affect the vapor orgas release rate and hence, the extent of the classified area are given in AppendixC.

5.2.5 Final Commentsë Consideration should always be given to the possibility that a gas which is

heavier than air may flow into areas below ground level (e.g., pits ordepressions). Conversely, a gas that is lighter than air may be retained athigh level (e.g., in a roof space).

ë Where the source of release is situated outside an area or in an adjoiningarea, the penetration of a significant quantity of flammable gas or vaporinto the area can be prevented by suitable means such as:

• Physical barriers

4 If the gas or vapor is significantly lighter than air, it will tend to move upwards. If significantly heavier thanair, it will tend to accumulate at ground level. For practical purposes, a gas or vapor which has a relative densitybelow 0.8 is regarded as lighter than air. If the relative density is 1.2, it is regarded as heavier than air. Betweenthese two values, both the possibilities should be considered.

REG – 003 of 29



• Maintaining a static overpressure in the area relative to theadjacent hazardous areas thus, preventing the ingress of thehazardous atmosphere.

• Purging the area with a significant flow of air thus, ensuring thatair escapes from all openings where the hazardous gas or vapormay enter.

5.3 Acceptable Classification AlternativesThe following methods are acceptable alternatives to modify the extent orchange the classification of a particular area:

ë Relocation of Process Equipment

Consider relocating the proposed process equipment so that the areawhere electrical equipment is located can remain non-classified. Considerthe use of walls or barricades.

ë Relocation of Electrical Equipment

Consider relocating the proposed electrical equipment outside theclassified area or relocating the electrical equipment from a Division 1 toa Division 2 area. Consider the use of walls or barricades.

ë Purging of the Enclosure/Room/Building

Consider purging the atmosphere of the electrical enclosure, room orbuilding to change the area classification.

There are three types of purging:

• Type X purging reduces the classification within an enclosure,room or building from Division 1 to non-classified.

• Type Y purging reduces the classification within an enclosure,room or building from Division 1 to Division 2.

• Type Z purging reduces the classification within an enclosure,room or building from Division 2 to non-classified.

The requirements for purging are stringent and may require de-energizing. When alarms and/or shutdowns are required for a purgedsystem, provision for sufficient purge pressure capacity and supplypressure to eliminate nuisance alarms should be made.

ë Pressurizing of the Enclosure/Room/Building

Consider pressurizing the enclosure, room or building to reduce bothDivisions 1 and 2 to a non-classified location.

REG – 003 of 29



ë Intrinsically Safe Equipment and Wiring

Intrinsically safe circuits should be considered for Class I, Divisions 1and 2 locations. Intrinsically safe equipment for process controlinstrumentation should also be considered. These electrical systems lendthemselves to the low energy requirements for this type of circuits.

Intrinsically safe equipment and its associated wiring must be installed sothat they are positively separated from the intrinsically safe circuits.

ë Non-Incendive Equipment

The use of non-incendive equipment should be considered forinstallations in Class I, Division 2 locations.

There are four basic types of non-incendive systems:

• Non-incendive circuits — wiring that, under normal conditions,cannot release sufficient energy to ignite a specific, ignitable,atmospheric mixture by opening, shorting or grounding. Inaddition, they will not permit ignition by thermal effect.

• Non-incendive contacts — current interrupting contacts incircuits that, under normal conditions, do not release sufficientenergy to ignite a specific, ignitable, atmospheric mixture byopening, shorting or grounding.

• Non-incendive components — components having contacts formaking and breaking a non-incendive circuit, and that are housedwithin an enclosure constructed so that the contacts are notcapable of causing ignition.

ë Oil-Immersed Contacts

For Class I, Division 2 locations, consider the use of ignition-capablecontacts immersed in oil.

ë Hermetically Sealed Contacts

For Class I, Division 2 locations, consider the use of contacts enclosed inhermetically sealed chambers.

ë Suitable Enclosures

For Class I, Divisions 1 and 2, consider the use of suitable enclosures tomeet the area classification requirements as necessary.

REG – 003 of 29



5.4 VentilationThe source of air used for ventilation should be from an area classified no higherthan the desired classification. If practical, the source of air should be from anon-classified area. In determining adequate ventilation, the gas/vaporconcentration can be considered homogeneous although it is recognized thatthere may be small “pockets” of higher concentration near sources of release.

5.4.1 Types of VentilationVentilation can be accomplished by the movement of air due to the wind and/orby temperature gradients or by artificial means. So two main types of ventilationare recognized:

ë Naturalë Artificial

5.4.2 Degree of VentilationThe degree or amount of ventilation, regardless of the type of ventilation, isdirectly related to the source of release and its corresponding release rate.Therefore, when adequate ventilation is provided, the dilution of the flammablemixture to below its lower flammability limit should entail the extent reductionof the classified area. Such reduction may be substantial enough to lead to aclassified area extent that is negligible and thus, considered a non-classified area.

5.4.3 Ventilation AvailabilityThe ventilation availability has an influence on the presence or formation of anexplosive atmosphere. Guidance on availability is given in Appendix D.

6. DocumentationAll area classification definition should be properly documented. All relevantinformation used should be referred to. Examples of such information, or of amethod used, would be:

ë Recommendations from relevant codes and standardsë Gas and vapor dispersion characteristics and calculations

The results of the area classification study and any subsequent alterations to itshall be placed on record.

REG – 003 of 29



Those properties that are relevant to area classification of all process materialsused in the facility should be listed and should include flashpoint, boiling point,ignition temperature, vapor pressure, vapor density and flammable limits.

Samples of tables for the recording of the physical /chemical properties of theflammable materials and the characterization of the sources of release are shownin Appendix E.

Area classification documents should include plans and elevations, asappropriate, showing both the type and extent of the classified areas. Where thetopography of an area influences the extent of the classified areas, this should bedocumented.

The documents should also include other relevant information:

ë The location and identification of sources of release. For large andcomplex facilities or process areas, it may be helpful to itemize ornumber the sources of release to facilitate cross-referencing between thedata sheets and the drawings.

ë The position of openings in buildings (e.g., windows, doors, inlets andoutlets of air for ventilation, etc.).

REG – 003 of 29



Appendix A

REG – 003 of 29



Start

Select process area

List all hazardous materials

Locate all hazardous materialsrelease sources

Is areaclassification

required?

Class I, Division 1 Class I, Division 2

Determine area boundaries

Yes

No

BA

Figure A.1 — Electrical Area Classification Flow Diagram

REG – 003 of 29



A

Evaluate classification alternatives

Relocation of process equipment /addition of barriers

Is there any conflictwith governing regulations,codes, standards or industry

practices?

B

Use of suitable enclosures

Use of non-incendive equipment,oil immersed and hermetically

sealed contacts

Use of intrinsically safe equipmentand wiring

Purging of enclosure, room orbuilding

Relocation of electrical equipmentoutside of electrical classifiedareas / addition of barriers

Electrical classification drawings

Summarize design criteria for areaclassification

Finalize and issuedesign criteria

Resolve conflict

Yes

No

Figure A.1 — Electrical Area Classification Flow Diagram (cont.)

REG – 003 of 29



Appendix B

REG – 003 of 29



Sources of ReleaseThe rigid application of the following examples is not intended and may need tobe varied to suit particular process equipment and situations.

Process PlantsSources giving a continuous grade of release:

ë The surface of flammable liquid in a fixed roof tank, with a permanentvent to the atmosphere

ë The surface of a flammable liquid which is open to the atmospherecontinuously or for long periods of time (e.g., an oil/water separator)

Sources giving a primary grade of release:

ë Pump, compressor or valve seals if release of flammable material duringnormal operation is expected

ë Water drainage points on vessels which contain flammable liquids, andwhich may release flammable material into the atmosphere while drainingoff during normal operation

ë Sample points which are expected to release flammable material into theatmosphere during normal operation

ë Relief valves, vents and other openings which are expected to releaseflammable material into the atmosphere during normal operation

Sources giving a secondary grade of release:

ë Pump, compressor or valve seals if release of flammable material duringnormal operation of the equipment is not expected

ë Flanges, connections and pipe fittings, where release of flammablematerial is not expected during normal operation

ë Sample points which are not expected to release flammable materialduring normal operation

ë Relief valves, vents and other openings which are not expected to releaseflammable material into the atmosphere during normal operation

REG – 003 of 29



Appendix C

REG – 003 of 29



Examples of Area Classificationë Area classification involves knowledge of the behavior of flammable

gases and liquids when they are released from containment and, soundengineering judgement based on equipment performance experience. Forthis reason, it is neither practicable nor possible to cover with theseexamples every conceivable variation of plant and process characteristics.The chosen examples are those that better describe the generalphilosophy of area classification and thus, allow for the safe use ofequipment in hazardous conditions.

ë In determining the distances shown in the diagrams, specific plantcomponent conditions have been given. The leakage conditions, as well,have been considered in relation to the mechanical performance of theequipment and other representative design criteria. The examples are justrepresentative of plant conditions since factors such as inventory,pressure, temperature, shut-off time, dispersion and other criteria relatedto plant components and process material affect the area classification.Therefore, these examples represent guidance only and will need to beadapted to take into account particular circumstances.

ë According to the selected governing code, standard or industrial practice,the shape and extent of the classified area may vary.

ë The intention of the examples that follow is not primarily that theyshould be used for area classification. Their main objective is todemonstrate typical results, which may be obtained in practice in anumber of different situations by following the guidance and proceduresof this document.

ë The figures shown correspond closely to those in various national orindustrial codes. They are only intended as a guide to the magnitude ofthe classified areas. In individual cases, the extent and shape of theclassified areas may be taken from API RP 500.

ë In practice, if it is intended to use the examples given in this documentfor area classification, account must be taken on the specific details ofeach individual case.

ë In each example, some but not all parameters that influence the type andextent of classified areas are given. The result of the classificationnormally gives a conservative result, taking into account those factorsthat have been specified and others that it has been possible to identifybut not quantify. This means that, if it is possible to specify the operatingparameters more closely, a more precise classification can be obtained.

REG – 003 of 29



Example No. 1A normal industrial pump mounted at ground level, situated outdoors, pumping flammable liquid:

Class I, Div. 1

Class I, Div. 2 Source of release (pump seal)

a

Ground levelSump

Not to scale

Main factors affecting the type and extentof classified areas

Ventilation

Type: Natural ArtificialDegree: Adequate Adequate*Availability: Poor Fair

Source of release Grade of release

Pump seal Primary and secondary

Product

Flash point Below process and ambient temperatureVapor density Greater than air

*Airflow from pump motor

Taking into account relevant parameters, the following are typical values which will be obtained for a pump havinga capacity of 50 m3/h (220 gpm) and operating at low pressure:

a = 3 m (10 ft) horizontally from source of release.b = 1 m (3 ft) from ground level and up to 1 m (3 ft) above the source of release.

b

REG – 003 of 29



Example No. 2A normal industrial pump mounted at ground level, situated indoors, pumping flammable liquid:

Class I, Div. 1

Class I, Div. 2 Source of release (pump seal)

a

Ground levelSump

Not to scale


Ventilation

Type: ArtificialDegree: AdequateAvailability: Fair


Pump seal (pump gland) Primary and secondaryand pool at floor level

Product



a = 1.5 m (5 ft) horizontally from source of release.b = 1 m (3 ft) from ground level and up to 1 m (3 ft) above the source of release.c = 3 m (10 ft) horizontally from source of release.

c

b

REG – 003 of 29



Example No. 3Control valve, installed in a closed process pipework system conveying flammable gas:

Class I, Div. 2 Source of release (valve)

Ground level

Not to scale


Ventilation

Type: NaturalDegree: AdequateAvailability: Fair


Valve shaft seal Secondary

Product

Gas PropaneGas density Greater than air


a = 1 m (3 ft) around the source of release.

a

REG – 003 of 29



Example No. 4A normal industrial pump mounted at ground level, situated outdoors, pumping flammable liquid:

Class I, Div. 1 Class I, Div. 2

a

Ground level

Not to scale


Ventilation

Type: NaturalDegree: AdequateAvailability: Poor


Liquid surface Continuous

Product



a = 3 m (10 ft) horizontally from the separator.b = 1 m (3 ft) above ground levelc = 7.5 m (22.5 ft) horizontally.d = 3 m (10 ft) above ground level.

Liquidc

bd

REG – 003 of 29



Example No. 5Flammable liquid storage tank, situated outdoors, with fixed roof and no internal floating roof tank:


Not to scale


Ventilation

Type: NaturalDegree: AdequateAvailability: Good


Liquid surface ContinuousVent opening PrimaryFlanges, etc. inside dike Secondary

Product



a = 3 m (10 ft) horizontally from the separator.b = 1 m (3 ft) above ground levelc = 7.5 m (22.5 ft) horizontally.

Liquid surface

c

b

a

Sump

REG – 003 of 29



Appendix D

REG – 003 of 29



The purpose of this Appendix is to assess the degree of ventilation by definingventilation conditions, and by means of explanations, examples and calculationgive guidance on the design of artificial ventilation systems.

The methods developed allow the determination of the type of classified area by:

ë Estimating the minimum ventilation rate required to prevent significantbuild-up of an explosive atmosphere and using this to calculate ahypothetical volume, Vz, which with an estimated dispersion time, t,allows determination of the degree of ventilation. It is not intended thatthese calculations be used to determine the extent of the classified area.

ë Determining the type of classified area from the degree and ventilationavailability and the grade of release.

Natural VentilationIn open-air5 situations, natural ventilation will often be sufficient to ensuredispersal of any explosive atmosphere that arises in the area. Natural ventilationmay also be effective in certain indoor situations (e.g., where a building hasopenings in its walls and/or roof).

Examples of natural ventilation:

ë Open structures, pipe racks, pump bays and the like.ë An open building, which taking in consideration the relative density of

the gases and/or vapors involved, has openings in the walls and/or roofso dimensioned and located that the ventilation inside the building, forthe purpose of area classification, can be regarded equivalent to an openair situation.

ë A building that is not an open building but has natural ventilationprovided by means of permanent openings made for ventilationpurposes.

Artificial VentilationThe artificial ventilation of an area may be either general or local and, for both ofthese, differing degrees of air movement and replacement can be appropriate.

Examples of general artificial ventilation:

ë A building that is provided with fans in the walls and/or in the roof toimprove the general ventilation in the building.

5 For outdoor areas, the evaluation of ventilation should normally be based on an assumed minimum windspeed of 0.5 m/s (1.12 mph), which will be present virtually continuously. The wind speed will frequently beabove 2 m/s (4.47 mph).

REG – 003 of 29



• An open-air situation provided with suitably located fans to improve the generalventilation of the area.

Examples of local artificial ventilation:

ë An air/vapor extraction system applied to an item of process equipmentwhich continuously or periodically releases flammable vapor.

ë A forced or extract ventilation system applied to a small, ventilated localarea where it is expected that an explosive atmosphere may otherwiseoccur.

Degree of ventilationThe effectiveness of the ventilation in controlling dispersion and persistence ofthe explosive atmosphere will depend upon the degree and ventilation availabilityand the design of the system. For example, ventilation may not be sufficient toprevent the formation of an explosive atmosphere but may be sufficient to avoidpersistence of an explosive atmosphere.

The following degrees of ventilation are recognized:

ë Adequate ventilation.ë Inadequate ventilation.

Ventilation availabilityThe ventilation availability (as well as the degree of ventilation) needs to be takeninto account when determining the type of area classification:

Three levels of ventilation availability should be considered:

Good — ventilation is present virtually continuously.

Fair — ventilation is expected to be present during normal operation.Discontinuities are permitted provided they occur infrequently and for shortperiods.

Poor — ventilation that does not meet the standard of fair or good, butdiscontinuities are not expected to occur for long periods.

Ventilation that does not even meet the requirements for poor availability mustnot be considered to contribute to the ventilation of the area.

When considering natural ventilation for outdoor areas, the evaluation ofventilation should normally be based on an assumed minimum wind speed of 0.5m/s (1.12 mph), which will be present continuously. In which case, theavailability can be considered as “good”.

REG – 003 of 29



When assessing the availability of artificial ventilation, the reliability andavailability of equipment such as standby blowers should be considered. Goodavailability will normally require that on system failure, the standby blowers startautomatically. However, if provision is made for preventing the release offlammable material when the ventilation has failed, the corresponding areaclassification does not require further modification.

The effect of ventilation on the area classification can be summarized in tableD.1.

Degree of ventilation

Adequate Inadequate

Ventilation Availability

Good Fair Poor All

Continuous

Primary

Secondary

Class I, Div. 1

Class I, Div. 1+

Class I, Div. 2

Class I, Div. 2

Class I, Div. 1

Class I, Div. 1Class I, Div. 1Class I, Div. 1


Class I, Div. 1+

Class I, Div. 2

Class I, Div. 1

Class I, Div. 1

Notes:1) "+" denotes "surrounded by".2) The Class I, Div. 2 area created by a secondary grade of release may exceed that attributable to a primaryor continuous grade of release; in which case the greater distance should be taken.

Table D.1 - Influence of ventilation on classifiedareas

Grade of release

REG – 003 of 29



Appendix E

REG – 003 of 29



No Flammable Material

Name Composition

Flashpoint

oCoF

kg/m3

lb/ft3

LFL

vol. % Vapor Pressure20 oC (68oF)

Volatility

kPapsi

Boiling Point

oCoF

RelativeDensity

IgnitionTemperature

oCoF

Remarks

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Facility: Area: Drawing:

Revision:Equipment: Date:

Notes:

Responsible:

(1) Check the appropriate box for the units being used.(2) In the absence of a vapor pressure value, the boiling point should beused.

Page:

REG-003 - Electrical Area Classification

Electrical Area Classification

Documents

Transcript of Electrical Area Classification