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Hazards, Accidents,Process Safety Management& Process Hazard Analysis

Well developed, time honored process:Ammonia Refrigeration

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Topics

Hazards and Accidents

Process Safety Management (PSM)

Process Hazard Analysis (PHA)

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Learning Objectives

Describe the hazard and accident-drivenstimulus for, and main components ofOSHAs Process Safety Managementstandard

Define Process Hazard Analysis and relatedterminology

Describe major hazard analysis methods Assess applicability (via pros and cons) of

major hazard analysis methods

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Hazards

An inherent physical or chemical characteristicthat has the potential for causing harm to people,the environment, or property1

Hazards are intrinsic to a material, or itsconditions of use

Examples

Hydrogen sulfidetoxic by inhalation

Gasolineflammable

Moving machinerykinetic energy, pinch points

1 AICHE Center for Chemical Process Safety

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Hazard Management:

The World as It Was Before

Reliant on Personal Responsibility

Experience = Expertise

Administration was not same asDocumentation

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The Rising Case for Change

2,500immediatefatalities;20,000+ total

Many otheroffsiteinjuries

1984Bhopal, IndiaToxic MaterialReleased

HAZARD:Highly Toxic

Methyl Isocyanate

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1984Mexico City, MexicoExplosion

300 fatalities

(mostly offsite)$20M damages HAZARD:

Flammable LPG

in tank

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1988Norco, LAExplosion

7 onsite fatalities, 42 injured

$400M+ damages

HAZARD:Flammable

hydrocarbon vapors

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1989Pasadena, TXExplosion and Fire

23 fatalities, 130 injured; damage $800M+

HAZARD:Flammable

ethylene/isobutanevapors in a 10 line

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Enter Process Safety Management

Integral part of OSHA Occupational Safety andHealth Standards since 1992

Known formally as: Process Safety Managementof Highly Hazardous Chemicals (29 CFR1910.119)

PSMapplies to most industrial processescontaining 10,000+ pounds of hazardous material

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In a Few Words, What is PSM?

Theproactive andsystematicidentification,evaluation, andmitigation or preventionof chemical releasesthat could occur as a

result of failures inprocess, procedures, orequipment.

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Whats Covered by PSM?

Process SafetyInformation

Employee Involvement Process Hazard Analysis

Operating Procedures

Training

Contractors

Pre-Startup SafetyReview

Mechanical Integrity

Hot Work

Management of Change Incident Investigation

Emergency Planningand Response

Compliance Audits

Trade Secrets

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Process Hazard Analysis

Simply, PHA allows the employer to:

Determine locations of potential safety problems

Identify corrective measures to improve safety

Preplan emergency actions to be taken if safetycontrols fail

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PHA Requirements

Use one or more establishedmethodologies appropriate to thecomplexity of the process

Performed by a team with expertise inengineering and process operations

Includes personnel with experience and

knowledge specific to the process beingevaluated and the hazard analysismethodology being used

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PHA Must Address (contd)

Consequences of failure of engineeringand administrative controls, especially

those affecting employees

Facility siting; human factors

The need to promptly resolve PHAfindings and recommendations

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Hazard Analysis Methodologies

What-If

Checklist

What-If/Checklist Hazard and Operability Study (HAZOP)

Failure Mode and Effects Analysis (FMEA)

Fault Tree Analysis An appropriate equivalent methodology

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What-If

Experienced personnel brainstorming aseries of questions that begin, "What if?

Each question represents a potential failurein the facility or misoperation of the facility

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What-If

The response of the process and/oroperators is evaluated to determine if apotential hazard can occur

If so, the adequacy of existing safeguards isweighed against the probability and severity

of the scenario to determine whethermodifications to the system should berecommended

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What-If Steps

1. Divide the system up into smaller, logicalsubsystems

2. Identify a list of questions for a subsystem3. Select a question

4. Identify hazards, consequences, severity,

likelihood, and recommendations5. Repeat Step 2 through 4 until complete

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What-If Question Areas

Equipment failures

Human error

External events

What if a valve leaks?

What if operator fails to restart pump?

What if a very hard freeze persists?

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What-If Summary

Perhaps the most commonly used method

One of the least structured methods

Can be used in a wide range of circumstances

Success highly dependent on experience of the

analysts

Useful at any stage in the facility life cycle Useful when focusing on change review

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Checklist

Consists of using a detailed list of preparedquestions about the design and operationof the facility

Questions are usually answered Yes orNo

Used to identify common hazards throughcompliance with established practices andstandards

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Checklist Question Categories

Causes of accidents

Process equipment

Human errorExternal events

Facility Functions

Alarms, construction materials, controlsystems, 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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Checklist Summary

The simplest of hazard analyses

Easy-to-use; level of detail is adjustable

Provides quick results; communicatesinformation well

Effective way to account for lessonslearned

NOT helpful in identifying new orunrecognized hazards

Limited to the expertise of its author(s)

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ChecklistSummary (contd)

Should be prepared by experiencedengineers

Its application requires knowledge of thesystem/facility and its standard operatingprocedures

Should be audited and updated regularly

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What-If/Checklist

A hybrid of the What-If and Checklistmethodologies

Combines the brainstorming of What-Ifmethod with the structured features ofChecklist method

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What-If/Checklist Steps

Begin by answering a series of previously-prepared What-if questions

During the exercise, brainstormingproduces additional questions to completethe analysis of the process under study

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What-If/Checklist Summary

Encourages creative thinking (What-If) whileproviding structure (Checklist)

In theory, weaknesses of stand-alone methods areeliminated and strengths preservednot easy todo in practice

E.g.: when presented with a checklist, it is typicalhuman behavior to suspend creative thinking

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HAZOP

Hazard andOperability Analysis

Identify hazards (safety, health,environmental), and

Problems which prevent efficient operation

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HAZOP

1. Choose a vessel and describe intention

2. Choose and describe a flow path

3. Applyguidewordtodeviation Guidewords include NONE, MORE OF, LESS

OF, PART OF, MORE THAN, OTHERTHAN, REVERSE

Deviations are expansions, such as NO FLOW,MORE PRESSURE, LESSTEMPERATURE, MORE PHASES THAN(there should be),

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HAZOP

(Illustrative example of HAZOP)

To Distillation Column

Feed Tank

Check

ValvePump

1. Vessel

3. REVERSAL OF FLOW

2. FLOW PATH

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HAZOP

4. Can deviation initiate a hazard of consequence?

5. Can failures causing deviation be identified?

6. Investigate detection and mitigation systems7. Identify recommendations

8. Document

9. Repeat 3-to-8, 2-to-8, and 1-to-8 until complete

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(Illustrative example of HAZOP)

HAZOP

To Distillation Column

Feed Tank

CheckValve

Pump

1. Vessel

3. REVERSAL OF FLOW

2. FLOW PATH

4. Distillation materials returning via pumparound

5. Pump failure could lead to REVERSAL OF FLOW

6. Check valve located properly prevents deviation

7. Move check valve downstream of pumparound

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Loss of Containment Deviations

Pressure too high

Pressure too low (vacuum)

Temperature too high Temperature too low

Deterioration of equipment

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HAZOPs Inherent Assumptions

Hazards are detectable by careful review

Plants designed, built and run to appropriatestandards will not suffer catastrophic loss ofcontainmentif ops stay within design parameters

Hazards are controllable by a combination of

equipment, procedures which are Safety Critical

HAZOP conducted with openness and good faithby competent parties

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HAZOP Pros and Cons

Creative, open-ended

Completenessidentifies all process hazards

Rigorous, structured, yet versatile

Identifies safetyandoperability issues

Can be time-consuming (e.g., includes operability)

Relies on having right people in the room Does not distinguish between low probability,

high consequence events (and vice versa)

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FMEA Failure Modes, Effects Analysis

Manual analysis to determine the consequencesof component, module or subsystem failures

Bottom-up analysis

Consists of a spreadsheet where each failure

mode, possible causes, probability ofoccurrence, consequences, and proposedsafeguards are noted.

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FMEAFailure 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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FMEA on a Heat ExchangerFailureMode

Causes ofFailure

Symptoms PredictedFrequency

Impact

Tube

rupture

Corrosion

from fluids(shell side)

H/C at

higherpressurethan

coolingwater

Frequent

hashappened2x in 10 yrs

Critical

couldcause amajorfire

Rank items by risk (frequency x impact)

Identify safeguards for high risk items

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FMEA Failure Modes, Effects Analysis

FMEA is a very structured and reliable methodfor evaluating hardware and systems.

Easy to learn and apply and approach makesevaluating even complex systems easy to do.

Can be very time-consuming (and expensive) anddoes not readily identify areas of multiple faultthat could occur.

Not easily lent to procedural review as it may notidentify areas of human error in the process.

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Fault Tree Analysis

Graphical method that starts with ahazardous event and works backwards toidentify the causes of thetop event

Top-down analysis

Intermediate events related to the top eventare combined by using logical operationssuch as AND and OR.

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FTA

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Fault Tree Analysis

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

event combinations Amenable tobut for comprehensive

systems, requiringuse of software

Not intuitive, requires training

Not particularly useful when temporalaspects are important

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Accident Scenarios May Be

Missed by PHA No PHA method can identify all accidents

that could occur in a process

A scenario may be excluded from thescope of the analysis

The team may be unaware of a scenario

The team consider the scenario but judge itnot credible or significant

The team may overlook the scenario

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Summary

Despite the aforementioned issues with PHA:

Companies that rigorously exercise PHA areseeing a continuing reduction is frequency andseverity of industrial accidents

Process Hazard Analysis will continue to playan integral role in the design and continuedexamination of industrial processes

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Using What You Learn

The ideas and techniques of ProcessHazard Analysis will be immediately

useful in upcoming recitation exercise onHazard Evaluation

Expect to be part of a Process HazardAnalysis Team early on in yourprofessional career

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Where to Get More Information

Chemical Safety and Hazard InvestigationBoards web site: www.csb.gov

MPRI web site: www. Mpri.lsu.edu/main/ Crowl and LouvarChemical Process Safety:

Fundamentals with Applications

KletzHAZOP & HAZAN: Notes on the Identificationand Assessment of Hazards

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