HAZOP Basics

HAZOPDesigned byHossam A. Hassanein

GoalsBasic understanding of HAZOPHAZOP requirementsHow it worksCase studyHAZOP teamAdvantage & disadvantage

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You and your family are on a road trip by using a car in the middle of the night. You were driving at 100 km/h and, it was raining heavily. The car hits a deep hole and, one of your tire blows. You hit the brake, but due to slippery road and your car tire thread was thin, the car skidded and was thrown off the road.

Scenario

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What is the cause of the accident?

What is the consequenc

e of the event?

What can we do to

prevent all those

things to happen in the first place?

What other possible

accidents might

happen on the road

trip?

Can we be prepared

before the accident occurs? Points to

Ponder

Definition

HAZOP(Hazard &

Operability) Study

- Is structured technique, which may be applied typically to a chemical production process, identifying hazards resulting from potential malfunctions in the process

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History5

Initially prepared by Dr. H G Lawley and associates of ICI at Wilton in 1960’s . In 1977, Chemical

Industries Association

published the edited version.

ICI expanded the procedure called HAZARD STUDY levels 1 to 6.

ICI Six Levels

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Project exploration / preliminary project assessment

Project definition

Design and procurement

During final stages of construction

During plant commissioning

During normal operation, some times after start-up

REMEBER

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HAZOP is an identifying

technique and not intended as a

means of solving problems

Features of HAZOP Study

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Subsystems of interest line and valve, etc Equipment, Vessels

Modes of operation Normal operation Start -up mode Shutdown mode Maintenance /construction / inspection mode

Trigger events Human failure Equipment /instrument/component failure Supply failureEmergency environment event


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Effects within plant Changes in chemical conditions Changes in inventory Change in chemical physical conditions

Corrective actions Change of process designChange of operating limitsChange of system reliability Improvement of material containment Change control system Add/remove materials


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How would hazardous conditions detected ?

During normal operation Upon human failure Upon component failure In other circumstances

Contingency actions Improve isolation Improve protection

Documents Needed for HAZOP Study

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Preliminary

HAZOP

– Process Flow Sheet or digram ( PFS or PFD )

– Description of the Process

Detailed

HAZOP

– Piping and Instrumentation Diagram (P & ID)

– Process Calculations

– Process Data Sheets

– Instrument Data Sheets

– Interlock Schedules

– Layout Requirements

– Hazardous Area Classification

– Description of the Process

Process Flow Diagram (PFD)

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Is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment.

The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations

Process Flow Diagram (PFD)Example

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P&ID

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A Piping and Instrumentation

Diagram - P&ID, is a schematic

illustration of functional

relationship of piping,

instrumentation and system equipment

components.

P&ID represents the last step in process

design.

P&ID Example

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HAZOP Procedure

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Possible

Causes

ProcessDeviation

s

PossibleConsequences

List of guide words for

generation of process

deviations

Definitions

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Study Nodes

The locations (on piping and

instrumentation drawings and

procedures) at which the process

parameters are investigated for

deviations.

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Intention

The intention defines how the plant is

expected to operate in the absence of deviations at the

study nodes.

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Deviations

Is a way in which the process conditions may depart from

their design/process intent

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Causes

These are the reasons why

deviations might occur

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Consequences

The results of the deviation, in case it

occurs.

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Safeguards

Facilities that help to reduce the occurrence

frequency of the deviation or to

mitigate its consequences.

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A short word to create the

imagination of a deviation of the design/process

intent.

Guide Words

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Guide Words Used (most 7 used)

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Guide Words MeaningNo Negation of the design intendLess Quantitative DecreaseMore Quantitative IncreasePart of Qualitative DecreaseAs Well As Qualitative IncreaseReverse Logical opposite of the intendOther Than Complete Substitution

HAZOP Deviation Guide 26

No,Not,None

Less,Low,Short

More,High,Long

Part of As Well As,Also

Other Than

Reverse

Flow No Flow Low Rate High Rate Missing Ingredient

Misdirection,Impurities

Wrong Material

Backflow

Pressure Open to Atmosphere

Low Pressure

High Pressure

____________ ____________ ____________ Vacuum

Temperature Freezing Low Temperature

High Temperature

____________ ____________ ____________ Auto refrigeration

Level Empty Low Level High Level Low Interface

High Interface

____________ ____________

Agitation No Mixing Poor Mixing Excessive Mixing

Mixing Interruption

Foaming,Extra Phase

____________ Phase Separation

Reaction No Reaction Slow Reaction

Runaway Reaction

Partial Reaction

Side Reaction

Wrong Reaction

Decomposition

Time Procedure

Skipped or Missed Step

To Short,To Little

Too Long,Too Much

Action Skipped

Extra Action(Shortcuts)

Wrong Action

Out of Order,Opposite

Speed Stopped Too Slow Too Fast Out of Synch

____________ Web or Belt Break

Backward

Special Utility Failure

External Leak

External Rupture

Tube Leak Tube Rupture

Startup,Shutdown,Maint

____________

Process Variable

Guide Words

Process Parameters

Physical parameters related to input medium properties

Physical parameters related to input medium conditions

Physical parameters related to system dynamics

Non-physical tangible parameters related to batch type processes

Parameters related to system operations

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Process parameters may generally be classified into the following groups:

Examples of Process Parameters

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Flow Pressure Composition Addition Separation Time

pH Signal Start/stop Operate Maintain Services

Communication Temperature Mixing Stirring Transfer Phase

Speed Particle size Measure Control Level Viscosity

Reaction Sequence

Simply How does it work?

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NODE: Pipe after pump and splitter

PARAMETER: Flow rate

GUIDE WORD: Less (less than normal value) DEVIATION: less flow than normalCAUSE: of deviation, can be more than one CONSEQUENCE: of the deviation/cause ACTION: initial idea for correction/ prevention/mitigation

A group members focus on the same issue

The HAZOP Process

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Monitor Actions For Completion

Agree Actions To Be Taken

Apply Risk Ranking

Associate Consequences

Identify Causes

Choose Deviation OR Parameters & Guide Words

Select Equipment Node

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Case Study

Case Study 1: Preliminary HAZOP on Reactor

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Cooling Water Refer to reactor system shown.The reaction is exothermic. A cooling system is provided to remove the excess energy of reaction. In the event of cooling function is lost, the temperature of reactor would increase. This would lead to an increase in reaction rate leading to additional energy release.The result could be a runaway reaction with pressures exceeding the bursting pressure of the reactor. The temperature within the reactor is measured and is used to control the cooling water flow rate by a valve.

Perform HAZOP Study

Case Study 1: Preliminary HAZOP on Reactor

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Guide Word Deviation Causes Consequences

Action

No No Cooling Cooling water valve malfunction

Temperature increase in reactor

Install high temperature alarm (TAH)

Reverse Reverse cooling flow

Failure of water source resulting in backward flow

Less cooling, possible runaway reaction

Install check valve

More More cooling flow

Control valve failure, operator fails to take action on alarm

Too much cooling, reactor cool

Instruct operators on procedures

As Well As Reactor product in coils

More pressure in reactor

Off-spec product Check maintenance procedures and schedules

Other Than Another material besides cooling water

Water source contaminated

May be cooling ineffective and effect on the reaction

If less cooling, TAH will detect. If detected, isolate water source. Back up water source?

Cooling Water

Case Study 2: Shell & Tube Heat Exchanger

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Using relevant guide words, perform HAZOP study on shell & tube heat exchanger

Case Study 2: Shell & Tube Heat Exchanger (Answer 1)

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ActionLess Less flow of

cooling water Pipe blockage Temperature of

process fluid remains constant

High Temperature Alarm

More More cooling flow

Failure of cooling water valve

Temperature of process fluid decrease

Low Temperature Alarm

More of More pressure on tube side

Failure of process fluid valve

Bursting of tube Install high pressure alarm

Contamination Contamination of process fluid line

Leakage of tube and cooling water goes in

Contamination of process fluid

Proper maintenance and operator alert

Corrosion Corrosion of tube

Hardness of cooling water

Less cooling and crack of tube

Proper maintainence

Case Study 2: Shell & Tube Heat Exchanger (Answer 2)

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Action

None No cooling water flow

Failure of inlet cooling water valve to open

Process fluid temperature is not lowered accordingly

Install Temperature indicator before and after the process fluid line Install TAH

More More cooling water flow

Failure of inlet cooling water valve to close

Output of Process fluid temperature too low

Install Temperature indicator before and after process fluid lineInstall TAL

Less Less cooling water

Pipe leakage Process fluid temperature too low

Installation of flow meter

Reverse Reverse process fluid flow

Failure of process fluid inlet valve

Product off set Install check valve Contamination Process fluid

contamination Contamination in cooling water

Outlet temperature too low

Proper maintenance and operator alert

HAZOP Team

5 to

7

mem

bers

Design EngineerProcess

EngineerOperations SupervisorInstrument

Design EngineerChemist

Maintenance Supervisor

Safety Engineer (team

leader)

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HAZOP AdvantageEasy to learn

Stimulates creativity and generates ideas

Systematic and through procedure

Participants gain valuable knowledge of process

Readily acceptable to regulatory authorities

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HAZOP DisadvantageTime consuming

Focusing too much on solutions

Team members allowed to divert into endless discussions of details

HAZOP is poor where multiple-combination events can have severe effects.

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Division Into SectionsGuideline

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Choices of lines–P&ID must be divided logically. Not too

many sections.

Each section should contain active components, which

gives rise to deviations. e.g piping which contains control valves can give rise to flow deviations, heat exchangers can cause Temp. deviations.

Materials in section – contain significant amount of hazardous materials.

Section based on process and states of materials. Only

1 process operation per 1 section.

Define each major process component as a section.

Define one line section between each major process

component.

Define additional line sections for each branches off the main process flow.

Define a process section at each connection to existing

equipment.

Define only one process section for equipment in

identical service.

Define only one line at the end of a series of

components if there are no other flow paths.

Define only one additional line section if there are alternative flow paths,

regardless of how many branches there are.

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Education

HAZOP Basics