Process Safety in Chemical Plants with Focus on HAZOP

by

S. S PIPARAFaculty at AVVIARE Educational Hub, Noida

and

Ex. Joint President GRASIM Industries Ltd., Nagda (India)

Second World Congress on Disaster Management

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Process Safety Management

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Root cause analysis of incidents The hazards associated with Unit

processes and Unit operations Process Safety and Equipment

Health

Experience Based Checklists and What-If /

Checklists Indices and Layers of

Protection Analysis (LOPA)

Analytical Failure Mode and Effects Analysis

(FMEA) Fault Tree Analysis and Event Tree

Analysis

Techniques in use are in one of three categories:TechniquesTechniques

1 2 3

Hazard Identification Techniques

Creative Brainstorming HAZOPS

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Process Hazard Analysis

An organized and systematic effort to identify and determine the significance of the hazards associated with the handling and processing of highly hazardous chemicals and assess the effectiveness of safeguards.

Catastrophic Release Major uncontrolled emission, fire or explosion that causes serious danger to employees in the workplace

Highly Hazardous Chemical

a substance that has toxic, flammable, explosive or reactive properties.

Process Any activity including use, storage, manufacturing, handling or on-site movement of a highly hazardous chemical

Safeguard Procedures and devices used to control process hazards and manage risk.

PreventionsProcedures and devices intended to stop the initiation of an undesired event or interrupt the escalation of an event sequence.

Mitigations Procedures and devices intended to respond to events and reduce the magnitude of undesired consequences.

Definitions

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Experience Based Hazard Identification Techniques

• Individual (of most limited value)• Informed Individual (safety specialist)• Outside standards such as:

• Center for Chemical Process Safety (CCPS)

• National Fire Protection Association (NFPA)

Checklist What-If/ Checklist •Natural extension of simple checklist•Begins to introduce a customization of the checklist to better fit the process•Best if done by experienced personnel•Most effective in early design stage of new projects.•Most often guided by a checklist of topics•Can be applied to a limited scope

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Process Upset Causes Consequences Safeguards Action Items

What if sample is spilled on operator

•Bottle breaks•Operator error

Operator burned, LTI

  Procedures and trainingPPE

Modify procedures to stress issue

What if batch temperature is too high?

Control failureOperator error

No issue, material is thermally stable

Procedures and training DCS

What if reactor leaks?

CorrosionMaintenance Error

Clean up costs only

PM ProgramERP

 Ensure adequate spill clean up materials are on hand

What if spill ignites and pool fire occurs indoors?

Leak plus spark from equipment

Operator fatality possible  Big $$$ loss

Fixed SprinklersAdequate drainageERP

Ensure adequate PM of electrical devices

Note: Action items are often abbreviated during the review and expanded to include additional explanation in the final report.

What-If Spreadsheet Example

Fault Tree Analysis

• Graphical representation of the combination of faults leading to a predefined undesired event

• This methodology uses logic gates to show all the credible paths from where the undesired event could occur

• A top down approach where each level is required to allow the next;

• The analyst asks what is required for the upper event or condition to exist?

• The pathway is plotted on the diagram using standard symbols

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Analytical Hazard Identification Techniques

• Use of a logic diagram to plot the path from an undesired outcome back to the basic equipment, systems and human failures, the Basic Events;

• Predominantly used for high consequence, low frequency events, to determine the adequacy of safeguards;

Basic Fault TreeBad Consequences

AndAnd

InitiatingEvent(s)

Failure of Protective Systems

• Equipment failure:• Corrosion• Fabrication error• Design error• Fire Exposure• Collision

• Operator error• Maintenance error

• Community ERP• Site ERP• 2nd Containment• ERS• SIS• Auto Shutdown • Alarms/Intervention• Process Control• Procedural Checklist• Procedures/Training• Mech Design/PM• Process Design

Frequency = F Probabilityof Failure

on Demand= P

Likelihood = FxP

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Event Tree Analysis

• An event tree is a graphical representation of the logic model that identifies and quantifies the possible outcomes following an initiating event.

• Use of a logic diagram to plot the path from a single initiating event through each decision point where consequences can be altered to arrive at the final potential consequence. At each decision point success or failure diverts the path.

• Event trees are used to identify the various accidents that can occur in a complex process

• Can be used with FMEA to develop safety oriented mechanical integrity programs.

Vapor CloudExplosion

Pool Fire

Reportable EnvironmentalIncident

Minor in-houseincident

FlammableLiquid isReleased

YES 90%

NO 10%

Ignition?

NO 90%

YES 10%

Delay?

NO 50%

YES 50%

90%

0.5%

0.5%

9.0%

Outcome FrequencyIncident development path

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Event Tree Analysis Example Quantified

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• Failure Modes and Effects Analysis (FMEA) is methodology for analyzing potential reliability problems early in the development cycle where it is easier to take actions to overcome these issues, thereby enhancing reliability through design.

• FMEA is used to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures.

Failure Mode Effect Analysis

• An assessment of equipment, components and systems to determine the way in which failures can occur and the consequences of component failure on systems and units.

• Most often qualitative but a quantitative assessment can be made.

• A “Bottom Up” approach• Spreadsheet style documentation

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FEMA

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Selecting a Hazard Identification Technique

Considerations

• Information available• Project stage• Personnel requirements• Personnel skill level• System complexity• System type• Schedule and time restrictions

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Selecting TechniqueMethod Pro Con

Checklist Good for high experience processes

Can be applied by one person

Good in early stages Can be tailored to area

of concern

Not comprehensive Limited by team experience Most applicable to preliminary

design stages

What-If Better than simple checklist

Can make use of inexperienced PHA personnel

Limited by team experience Not comprehensive

FMEA Can support fault tree Can support MI

Can miss interactions and multiple failure modes

Equipment oriented Poor for un-steady state

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Brainstorming

• An unstructured technique used by a team to gather all ideas about a topic, without specific analysis of those ideas. • The scribe will typically

write down all that is said by the team members for later analysis. (Flip Chart)

• May be leader or checklist driven:

“How can the pump fail?”• Common method within a

PHA team

Creative Hazard Identification Techniques

• The classic method encourages free thinking and creativity, no idea is turned away.

• Only after the team’s brainstorming has reached a logical end, are documented ideas analyzed, and possibly discarded.

• Brainstorming can be a good way of encouraging team participation.

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HAZOP - HAZard & OPerability

• First developed at ICI in the UK in 1964 this method is a natural extension of standardized checklists.

• Where checklists count on past experience, HAZOPs develops ‘synthetic experience’ by hypothesizing deviations from desired performance.

• Most applicable to new and novel processes where experience is lacking.

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• The basic premise of HAZOPS is:

All hazardous material incidents are instigated by a deviation from the desired operating state or condition.

• If we can predict all deviations and analyze them before we operate a new process then we can head off the undesired consequences.

Forewarned is Forearmed

HAZOP - HAZard & OPerability

HAZOP Approach

Parameter + Guided words

Deviation Cause Consequence Safeguard Action

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Define Intended Process

Repeat

Intention: • The Intention defines, How the selected

section/unit is expected to operate Parameters:• Aspects of a process that describe it physically

or in terms of what is happeningSome Parameters:• Flow • Pressure • Temperature • Level • Phase • Viscosity • Concentration

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HAZOP APPROACH

Guidewords:• These are simple words, which are used to

qualify the intentions in order to guide and stimulate the thinking process and so discover deviations.

Some Guidewords: • No/None • More • Less• Reverse • Other than • As well as • Part of

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HAZOP APPROACH

HAZOP APPROACHGuideword Meanings

Guideword Meaning Example Parameter: Flow

No/None None of design intent is achieved No Flow

More Quantitative increase in a parameter More Flow

Less Quantitative decrease in a parameter Less Flow

Reverse Logical opposite of the design intent occurs

Reverse Flow

Other than Complete substitution – another activity takes place

Boiling

As well as An additional activity occurs Chemical Reaction

Part of Only some of the design intent is achieved

-----

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Deviations: • Deviation means departure from the design

intent

These are discovered by systematically applying the guidewords

Causes: • Reasons for deviations

Consequences:• Results of deviations

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HAZOP APPROACH

Safeguards:• Procedures or devices exists to control

causes or mitigate consequences• Prevention measures or • Mitigation measures or • Combination of both

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HAZOP APPROACH

• HAZOPS uses a standard list of “Guidewords” as modifiers to process Parameters to hypothesize Deviations from the desired intent.

Deviation = Guideword + Parameter

• The Deviations are analyzed by the team to determine if a hazardous condition would occur, or if an important operating upset is discovered.

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HAZOP APPROACH SUMMARY

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HAZOP APPROACH SUMMARY

HAZOP Study Team

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Leader

Instrumentation supervisor

Operator

Chemist

Chemical Engineer

Maintenance Supervisor

Specialist

OperationsSupervisor Design Team

Member

Common Team Size:4-7 people

Scribe

• HAZID - To identify hazards and potential accident scenarios

to be performed at the initial stage of a project

• HAZOP - To identify specific hazards arising from process

deviation, to evaluate adequacy of existing safeguards and to

identify additional mitigating measures

to be performed at different stages throughout the entire

project life

• QRA - To assess personnel risk posed by potential hazard

scenarios

to be performed at the initial stage of the project with further

updating at a later stage

Hazard Studies

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Safety Review Checklist Preliminary Hazard Analysis What-If Abbreviated HAZOP Study

Used in preliminary hazard evaluation studies to provide a general overview of existing risks (Usually not too time consuming)

What-If/Checklist Detailed and complete HAZOP

Study Failure Mode and Event

Analysis

Used to develop a more detailed analysis of potential risks

Fault Tree Analysis Event Tree Analysis Cause Consequence Analysis Human Reliability Analysis

Used in conjunction with quantitative risk analysis to establish a high level detail about risks (Usually used for specific area or Unit Operations)

Risk Identification TechniquesRisk Identification Techniques When you might use themWhen you might use them

Identifying the Risk

HAZARD IDENTIFICATION METHODS:

- Process hazard checklist

- Hazard survey: DOW index

- HAZOP hazard & operability study

- Safety review

System description

Hazard identification

Scenario identification

Accident

probability

Accident

consequences

Risk determination

Risk &

Hazard

acceptable

?

Modify design

Accept system

Y

NEXTREMES

- Low probability

- Minimal consequences

RISK ASSESSMENT:

- What can go wrong & how ?

- What are the chances ?

- Consequences ?

Risk Assessment Procedure

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THANKS

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