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Overview ofProcess Hazard

Analysis(PHA)

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Factors

InfluencingIncidents

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Causes of Accidents and IncidentsIncidents and Accidents are caused by

either unsafe behaviours (substandard

practice) and/or unsafe conditions

(substandard designs).

Unsafe behaviours are handled by Occupational Safety Program,

Unsafe conditions are managed through Process Safety Programs.

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Accident Causation Models

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DOMINO EFFECT

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LOSS CAUSATION MODEL

LACK OF

CONTROL

INADEQUATE

PROGRAM

BASIC

CAUSES

PERSONALFACTORS

&JOB

FACTORS

IMMEDIATE

CAUSES

SUBSTANDARD

ACTS&

CONDITIONS

INCIDENT

CONTACTWITH

ENERGYOR

SUBSTANCE

LOSS

PEOPLEPROPERTYPROCESS

PLANET

LOSS CAUSATION

PROBLEM SOLVING

Workersexposedto hazards

THRESHOLD

OSH-MSSafe Operating Procedures, Training,Supervision, Maintenance, PPE

Activity: PREVENTION Activity: MITIGATION

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ACCIDENT RATIO STUDY

SERIOUS OR DISABLING

Including disabling and serious injuries

MINOR INJURIES

Any reported injury less than serious

PROPERTY DAMAGE ACCIDENTS

All types

INCIDENTS WITH NO VISIBLE

INJURY OR DAMAGE

Near-miss accident

10

30

600

1

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Process Hazards

HAZARDOUS MATERIALS + PROCESS CONDITIONS

Flammable materialsCombustible materialsUnstable materials

Reactive materialsCorrosive materialsAsphyxiatesShock-sensitive materialsHighly reactive materials

Toxic materialsInert gasesCombustible dusts

High temperaturesExtremely lowtemperatures

High pressuresVacuumPressure cyclingTemperature cyclingVibration/liquid

hammeringRotating equipmentIonizing radiationHigh voltage/currentErosion/Corrosion

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Human Factors or Errors

HUMAN FAILURE

ERRORS VIOLATIONS

Deliberate actions Different from those prescribed Carries known associated risks Ignores operational procedures Violation errors occur because of a

perception of lack of relevance, timepressure or laziness.

Competency exists Intentions are correct Slips occur while

carrying out habitual,routine, skill basedactivity.

Incorrect intention Inadequate knowledge Incorrect information processing Inadequate training Mistakes occur because of incorrect

assumptions or incorrect tunnel

vision application of rules.

SLIPSMISTAKES

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Process HazardAnalysis

(PHA)Methodologies

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PHA Methodologies

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Process Hazards Analysis

PROCESS HAZARDS ANALYSIS

What can go

wrong?

How likely is

it?

What are the

consequences?

PROCESS HAZARDS ANALYSIS STRUCTURE

FOUNDATION FOR PROCESS HAZARDS ANALYSIS

HistoricalExperience

PHAMethodology

Knowledgeand Intuition

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Qualitative Risk Analysis

Process Hazards Analysis isthe predictive identification

of hazards, their cause &consequence and thequalitative estimation oflikelihood and severity.

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Qualitative vs. Quantitative

PROCESS HAZARDS ANALYSIS RISK ANALYSIS

IDENTIFIES HAZARDS, estimateslikelihood and severity, suggestsimprovements.

USE ON EVERY PROJECT

QUALITATIVE - based onexperience, knowledge and creativethinking.

Most often done byMULTIDISCIPLINARY TEAM

Several methodologies available What-if or Hazid What-if/Checklist HAZOP FMEA Preliminary Hazards Analysis

ASSESSES HAZARDS

SELECTIVE - use when othermethods prove inadequate orexcessive in cost.

QUANTITATIVE - requiresextensive data and specialexpertise.

Done by ONE OR TWO SPECIALLYTRAINED PEOPLE

Also called: Hazan Risk Assessment Probabilistic Risk Assessment

(PRA) Quantitative Risk Assessment

(QRA)

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Process Hazard AnalysisSimply, PHA allows the employer to:

Determine locations of potential safetyproblems

Identify corrective measures to improve safety Preplan emergency actions to be taken if

safety controls fail

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PHA Must Address

The hazards of the process Identification of previous incidents with likely potential

for catastrophic consequences

Engineering and administrative controls applicable to

the hazards and their interrelationships Consequences of failure of engineering and

administrative controls, especially those affectingemployees

Facility siting; human factors

The need to promptly resolve PHA findings andrecommendations

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PROJECT PHASE

Conceptual Processdevelopment

Projectsanction

Design, engineering,construction

Handover

operation

Stage 1

Concept

Stage 2

Processdesign

Stage 3

DetailedEngineering

Stage 6

Post-commissioning

Stage 5

Pre-Commissioning

Stage 4

Construction

Relationship of six-stage process study system to project life-cy

Safety issues must be embedded within all project life-cycle

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PHA and project phaseMethodused

Project life cycle stage

0 1 2 3 4 5 6 7

Checklist X X X X X X X X

RR X X (X) (X)

What-If X X X X

FMEA (X) X X (X)

LOPA X X X

HAZOP (X) X X

PHR X (X)

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What If

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What-If

Experienced personnel brainstorming a series ofquestions that begin, "What if?

Each question represents a potential failure in thefacility or mis-operation of the facility

The response of the process and/or operators isevaluated to determine if a potential hazard can occur

If so, the adequacy of existing safeguards is weighedagainst the probability and severity of the scenario todetermine whether modifications to the systemshould be recommended

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What-If Steps

1. Divide the system up into smaller, logicalsubsystems

2. Identify a list of questions for asubsystem

3. Select a question

4. Identify hazards, consequences, severity,likelihood, and recommendations

5. Repeat Step 2 through 4 until complete

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What-If Question Areas Equipment failures

What if a valve leaks?

Human error

What if operator fails to restart pump?

External events

What if a very hard freeze persists?

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What IfWhat If? Initiating Cause Consequence

1. There is

higher

pressure in the

vessel

1.1 External fire in

the process area

1.1 potential increase in temperature and

pressure leading to possible leak or

rupture. Potential release of flammable

material to the atmosphere. Potential

personnel injury due to exposure.

1.2 pressure

regulator for inert

gas fails open

1.2 potential for vessel pressure to

increase up to the inert gas supply

pressure. Potential vessel leak leading to

release of flammable material to theatmosphere. Potential personnel injury

due to exposure.

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Checklist

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Checklist Review an installation against known hazards

identified on previous studies of similar plant

Examine the checklist for relevance to plant

being studied Ask questions based on a pre-defined list

The checklist is a corporate memory of whatcould go wrong

Should be augmented by industrial-wide experiencewhen available

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Strength of checklist Is quick and simple to perform and is easily

understood

Makes use of existing experience and

knowledge of previous systems Helps check compliance with standard practice

and design intention

Ensures that known hazards are fully explored

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Weakness of checklist Does not provide a list of initiating events

(failure cases) for a QRA

May not be comprehensive and does not

encourage analysts to consider new or unusualhazards

Highly dependent upon the quality of theprepared checklists

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Checklist Question Categories Causes of accidents

Process equipment

Human error

External events

Facility Functions

Alarms, construction materials, control systems,

documentation and training, instrumentation, piping,pumps, vessels, etc.

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Checklist Questions

Causes of accidents Is process equipment properly supported?

Is equipment identified properly?

Are the procedures complete?

Is the system designed to withstand hurricane winds?

Facility Functions

Is is possible to distinguish between different alarms?

Is pressure relief provided?

Is the vessel free from external corrosion?

Are sources of ignition controlled?

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Hazard Indices

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Hazard Indices Hazard indices give a quantitative indication of

the relative potential for hazardous incidentsassociated with a given plant or process. Theyare used to most effect at the early design

stage of a new plant.

The best known hazard indices are the DowIndex (1981) and the Mond Index (1979).

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Operates like an income tax form.

Penalties for unsafe situations

Credits for control and mitigation

Produces a number - the bigger the numberthe greater the hazard.

Only considers flammable materials

Not effective for procedures.

Dow Fire and Explosion Index

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Dow Fire & Explosion Index

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Considers toxic materials only.

Includes simple source and dispersion models.

Not effective for procedures.

Dow Criteria: If sum of F&EI and CEI > 128,then more detailed hazard review procedurerequired.

Dow Chemical Exposure Index (CEI)

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Mond Index

Objectives of Mond Index

To Identify, Assess and Minimize potential hazards onchemical plants units for new and existing processes

About Mond Index

Index primarily concerned with fire and explosion problem.

Toxicity is considered only as possible complicating factor.

Method gives credits for plant safety features (both hardwareand software).

Mond Index

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Mond Index Procedure1. Divide plant into units and each unit is assessed individually2. Select ion of key material present in the unit.

Key material is the most dangerous chemicals (inherent properties),which higher possibility for combustion, explosion or exothermicreaction.

3. Calculation of Factors Material Factor, B

Special Material hazards, M

Special Process hazards, S

Quantity Hazards, Q

Layout Hazards, L Acute Health Hazards, T

4. Calculation of Indices - Dow Index (D), Fire Index (F), ExplosionIndex (E), Overall Hazard Rating (R).

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The most important criteria - overall hazard rating, R

Overall Hazard Rating Category

0-20 Mild

20-100 Low100-500 Moderate

500-1100 High (group 1)

1100-2500 High (group 2)

2500-12,500 Very high

12,500-65,0000 Extreme

> 65,000 Very extreme

Mond Index Criteria

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HAZID

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HAZID Performed by a team of multidisciplinary

experts

The analyses are carried out based on area by

area basis It is focusing on location of the process

The discussion proceeds through theinstallations modules or operations using

guide words to identify potential hazards, itscauses, and possible consequences

The outcomes are summarised in HAZID Log

Sheet 39

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HAZID Guidewords

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HAZID Guidewords Port Facility

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HAZID Log SheetRefNo

Guideword

HazardDescription

Conse-quences

Risk Potential Safeguards/mitigating

features

Action /commentcons Freq

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HAZOP

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HAZOP

Performed by a team of multidisciplinary experts The process is divided into distinct subsections or

nodes

It is focusing on plant component/equipment

On each node, detailed brainstorming is conductedfacilitated by a HAZOP Leader

Based on the design intent of each equipment specified by thenode, possible deviations are examined, aided by guidewords

and process parameters

Causes, consequences are identified and existing protectionprescribed by the design are assessed. Based on these,recommendations are put forward

The outcome is summarized in a HAZOP Log Sheet 44

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HAZOP Guidewords No: negation of design intention; no part of design intention is

achieved but nothing else happens More: Quantitative increase

Less: Quantitative decrease

As well as: Qualitative increase where all design intention is

achieved plus additional activity

Part of: Qualitative decrease where only part of the designintention is achieved

Reverse: logical opposite of the intention

Other than: complete substitution, where no part of the originalintention is achieved but somethingquite different happen

Contamination, corrosion, sand deposits etc

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HAZOP Log Sheet

Deviation Causes Consequences Protection Action

Guideword +

Parameter

Guideword: No,

Less, More,

reverse etc

Parameter: Flow,

temperature,

level etc

Possible causes of

the deviation

Effect of deviation

of plant safety and

operability

Safety

provision

already

considered.

- Prevent

causes

- prevent/

reduce

consequence

- monitor/

detect

Is the protection

sufficient?

If not, propose

suitable action or

recommendation

Based on the selected NODE and the design intent ofthe node, HAZOP study is conducted. The output issummarised in HAZOP Log Sheet

Example: Simplified HAZOP Log Sheet

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LOPA

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LOPA

LOPA is a semi-quantitative risk analysis technique that is appliedfollowing a qualitative hazard identification tool such as HAZOP.

Similar to HAZOP LOPA uses a multi-discipline team

LOPA can be easily applied after the HAZOP, but before fault treeanalysis

LOPA focuses the risk reduction efforts toward the impact eventswith the highest risks.

It provides a rational basis to allocate risk reduction resourcesefficiently.

LOPA suggests the required Independent Layer of Protection (IPL)required for the system to meet the required Safety Integrity Level(SIL)

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LOPA Methodology There are five basic steps in LOPA:

1. Identify the scenarios

2. Select an accident scenario

3. Identify the initiating event of the scenario anddetermine the initiating event frequency (events peryear)

4. Identify the Independent Protection Layers (IPL)

and estimate the probability of failure on demand ofeach IPL

5. Estimate the risk of scenario

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LOPA

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LOPAConsequence

& Severity

Initiating

event(cause)

Initiating

eventchallenge

frequency

/year

Preventive independent protection

layersProbability of failure on demand

(PFD)

Mitigation

independentprotection

layer (PFD)

Mitigated

consequence

frequency

/year

Process

design

BPCS Operator

response

to alarm

SIF

(PLC

relay)

iJiiIi

ij

J

j

I

i

C

i

PFDPFDPFDf

PFDff

...21

1

ieventinitiatingforCeconsequencagainstprotects

thatIPLjththeofdemandonfailureofyprobabilit

ieventinitiatingforrequencyfrequency

ieventinitiatingforCeconsequencforfrequency

ij

I

i

C

i

PFD

f

f

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Failure Modes,Effects Analysis

(FMEA)

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FMEA Failure Modes, Effects Analysis Performed by a team or a single analyst Systematic review

Considers each component in turn

Subjectively evaluates effects of failure

Based on tabular format

FMECA includes critical analysis

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FMEA Failure Mode Keywords Rupture

Crack

Leak

Plugged Failure to open

Failure to close

Failure to stop

Failure to start Failure to continue

Spurious stop

Spurious start

Loss of function

High pressure

Low pressure High temperature

Low temperature

Overfilling

Hose bypass Instrument bypassed

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Example: FMEA on a Heat ExchangerFailure

Mode

Causes of

Failure

Symptoms Predicted

Frequency

Impact

Tuberupture

Corrosionfrom fluids

(shell side)

H/C athigher

pressurethancoolingwater

Frequent has

happened2x in 10 yrs

Critical could

cause amajorfire

Rank items by risk (frequency x impact) Identify safeguards for high risk items

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Fault-TreeAnalysis

(FTA)

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Fault Tree Analysis

Provides a traceable, logical, quantitativerepresentation of causes, consequences and eventcombinations

Not intuitive, requires training

Top-down analysis

Graphical method that starts with a hazardous eventand works backwards to identify the causes of the topevent

Intermediate events related to the top event arecombined by using logical operations such as ANDand OR.

Not particularly useful when temporal aspects are

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Example of FTA

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FTA Procedure

makedecision:

acceptable?

identify top event

construct the fault tree

analyze qualitatively

analyze quanitatively

accept system

YES

NO

develop improvements

FTA Nomenclature

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PHRMethodSelectionDecisionTree