Short Course on HAZOP and Risk Assessment UDPS 1 Hazard and Operability Hazard and Operability Study Study (HAZOP) (HAZOP) 2 I suppose that I should have done that HAZOP Study!
Short Course on HAZOP and Risk Assessment
UDPS 1
Hazard and Operability Hazard and Operability Study Study
(HAZOP)(HAZOP)
2
I suppose that I should have done that
HAZOP Study!
Short Course on HAZOP and Risk Assessment
UDPS 2
3
A scenario…A scenario…
You and your family are on a road trip by using a car inthe middle of the night. You were replying a textmessage while driving at 100 km/h and it was rainingheavily. The car hits a deep hole and one of your tireblows.
You hit the brake, but due to slippery road and your cartire thread was thin, the car skidded and was thrown offthe road.
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Points to ponderPoints to ponder
What was the cause of the accident?
What was the consequence 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?
Short Course on HAZOP and Risk Assessment
UDPS 3
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Can we make it more systematic?Can we make it more systematic?Parameter Guideword Possible
Causes
Consequences Action Safeguard
Car speed Too fast
Too slow
Rushing Skidded when emergency brake
- Slow down
- Speed up
-ABS brake system
-Safety belt
- Air bag
Tire No thread
Less thread
Tire too old, often speeding and emergency break
Car skidded - Check frequently
- Have spare tire
Window visibility
Low
Very low
Rain Cannot see the road
Car light Dim
No light
-Stop car
-Go to nearest garage
-Use emergency signal
Road With holes
Rocky
Breaks the car tire
- Put a signboard
-Street lights
Travel time Night
Foggy
No street light -Travel during daylight
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What is a HAZOP study?What is a HAZOP study?
Systematic technique to IDENTIFY potential HAZardand OPerating problems
Involves a multi-disciplinary team methodically“brainstorming” the plant design
A qualitative technique based on “guide-words” tohelp provoke thoughts about the way deviations fromthe intended operating conditions can lead tohazardous situations or operability problems
Short Course on HAZOP and Risk Assessment
UDPS 4
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What is a HAZOP study?What is a HAZOP study?
A HAZOP study is an examination procedure.
Its purpose is to identify all possible deviation from theway in which a design is expected to work and to identifyall the hazards associated with these deviations.
When deviation arise that results in hazards, action aregenerated that require design engineers to review andsuggest solutions to remove the hazard or to reduce itsrisk to an acceptable level.
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Potential Hazard Potential Hazard ANDAND Operability Operability ProblemsProblems
Short Course on HAZOP and Risk Assessment
UDPS 5
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ExampleExample
A study was commissioned for a new plant.
Some two years previously, and for the first time, asimilar study had been carried out on differentplant at the same site which was then in theprocess of being designed.
Before the latest review commenced, theProduction Manager expressed the hope that thesame benefits would accrue as before, stating that
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Definition of Hazard & OperabilityDefinition of Hazard & Operability
Hazard - any operation that could possibly causea catastrophic release of toxic, flammable orexplosive chemicals or any action that could resultin injury to personnel.
Operability - any operation inside the designenvelope that would cause a shutdown that couldpossibly lead to a violation of environmental, healthor safety regulations or negatively impactprofitability.
Short Course on HAZOP and Risk Assessment
UDPS 6
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BenefitsBenefits
The circumstances when HAZOPs are likely to producebenefits are:– during the design or installation of any new plant or process, or
major modification to an existing one;– when there are unique hazards such as environmental hazards
and quality or cost issues associated with the operation;– following a major incident involving fire, explosion, toxic release
etc; and– to justify why a particular code of practice, guidance note or
industry code is not to be followed.
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When should a HAZOP be heldWhen should a HAZOP be held
During various stages of plant design – At the beginning of the project as a ‘safety and environmental
specification’– Towards the end of process definition, when the Process Flow
sheets are available as a Safety and Environmental Review– When P&IDs are at ‘Approved for Design’ stage (Final design
HAZOP) During construction site inspections ensure that
recommendations arising from the HAZOP or other safety and environmental reviews are being implemented.
A pre-commissioning study reviews plant procedures and perform a conventional safety audit
Once operational, an audit of plant and procedures at regular interval ensures ongoing safety awareness
Short Course on HAZOP and Risk Assessment
UDPS 7
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HAZOP study of existing plantHAZOP study of existing plant
Can be done at any time Mainly used to improve operating procedures or when
modifying plant Sometimes used to identify possible improvements in
plants where accident or incident rate is abnormally high Can be used in conjunction with plant safety audits Needs exceptional care to fully define the scope and
aims of the study Despite detailed operation knowledge, much of the
original design intent is often unknown
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Simple Example of a HAZOP StudySimple Example of a HAZOP Study
Diammonium Phosphate (DAP) Production
Phosphoric acid and ammonia are mixed, and a non-hazardousproduct, diammonium phosphate (DAP), results if the reaction ofammonia is complete. If too little phosphoric acid is added, thereaction is incomplete, and ammonia is produced. Too littleammonia available to the reactor results in a safe but undesirableproduct.
Both chemicals will be used in large quantities and inconcentrated form. Due to the highly corrosive nature ofboth chemicals, the project team was assigned toinvestigate the hazards posed to staff from the reactionresulting from study line 1 (phosphoric acid delivery line).
Short Course on HAZOP and Risk Assessment
UDPS 8
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Production of DAP (continuous process)Production of DAP (continuous process)
Ammonia
Valve B
Reactor
Diammonium Phosphate (DAP)
Valve C
Valve A
Phosphoric Acid
Study line 1Phosphoric acid delivery line
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HAZOP Study Report on line 1 of DAP HAZOP Study Report on line 1 of DAP
Short Course on HAZOP and Risk Assessment
UDPS 9
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Preliminary HAZOP ExamplePreliminary HAZOP Example
TC
Cooling Coils
MonomerFeed
Cooling Water to Sewer
Cooling Water In
Thermocouple
Refer to reactor system shown.
The reaction is exothermic. A coolingsystem is provided to remove theexcess energy of reaction. In the eventof cooling function is lost, thetemperature of reactor would increase.This would lead to an increase inreaction rate leading to additionalenergy release.
The result could be a runaway reactionwith pressures exceeding the burstingpressure of the reactor. Thetemperature within the reactor ismeasured and is used to control thecooling water flow rate by a valve.
Perform HAZOP Study
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Preliminary HAZOP on Reactor Preliminary HAZOP on Reactor -- ExampleExample
Guide Word Deviation Causes Consequences Action
NO No cooling Temperature increase in reactor
REVERSE Reverse cooling flow
Failure of water source resulting in backward flow
MORE More cooling flow
Instruct operators on procedures
AS WELL AS Reactor product in coils
Check maintenance procedures and schedules
OTHER THAN Another material besides cooling water
Water source contaminated
Short Course on HAZOP and Risk Assessment
UDPS 10
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Preliminary HAZOP on Reactor Preliminary HAZOP on Reactor –– AnswerAnswer
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 inefffective and effect on the reaction
If less cooling, TAH will detect. If detected, isolate water source. Back up water source?
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Term Definition
Cause The reason(s) why the DEVIATION could occur. More CAUSES can be identified for one DEVIATION.
Comments Any remarks to be given to the RECOMMENDATIONS or which, in another way, showed up during the HAZOP sessions.
Consequence The results of the DEVIATION, in case it occurs. CONSEQUENCES may both comprise process hazards and operability problems, like plant shutdown. More CONSEQUENCES can follow from one cause and, in turn, one CONSEQUENCE can have several CAUSES.
HAZOP Terminology HAZOP Terminology -- 11
Short Course on HAZOP and Risk Assessment
UDPS 11
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Term DefinitionDeviation A way in which the process conditions may depart from their
INTENTION.
Intention / Design intent
Description of how the process is expected to behave at the Study Line. This is qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or quantitatively in the process parameters, like temperature, flow rate, pressure, composition, etc.
Keyword/ Guideword
A short word to create the imagination of a DEVIATION of the INTENTION. The mostly used set of Guidewords is: NO, MORE, LESS, AS WELL AS, PART OF, OTHER THAN and REVERSE. The GUIDEWORDS are applied, in turn, to all the PARAMETERS, in order to identify unexpected and yet credible DEVIATIONS from the INTENTION.
HAZOP Terminology HAZOP Terminology -- 22
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Term DefinitionParameter The relevant parameter for the condition(s) of the process,
e.g., pressure, temperature, composition, etc.
Study Line/ Node A specific location in the process in which (the deviations of)the process intention are evaluated. Examples might be:separators, heat exchangers, scrubbers, pumps, compressors,and interconnecting pipes with equipment
Recommendation Activities identified during a HAZOP study for follow-up. Thesemay comprise technical improvements in the design,modifications in the status of drawings and processdescriptions, procedural measures to be developed or furtherin-depth studies to be carried out.
HAZOP Terminology HAZOP Terminology -- 33
Short Course on HAZOP and Risk Assessment
UDPS 12
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HAZOP Terminology HAZOP Terminology -- 44
Term Definition
Action – Where a credible cause results in a negative consequence, it mustbe decided whether some action should be taken. It is at this stagethat consequences and associated safeguards are considered. If it isdeemed that the protective measures are enough, then no actionneed be taken, and words to that effect are recorded in the Actioncolumn.
– Actions fall into two groups:• Actions that remove the cause.
• Actions that mitigate or eliminate the consequences.
– Whereas the former is to be preferred, it is not always possible,especially when dealing with equipment malfunction. However,always investigate removing the cause first, and only wherenecessary mitigate the consequences.
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HAZOP Planning and ExecutionHAZOP Planning and Execution
PLANSelect Team
Examine SystemKeywords
CLOSE OUTRecord/File Completed
ActionsTRACK
ACTIONSHAZOP Review Meeting
TEAMSystem
AssessmentTeam Activity
REPORTAction List
HAZOP Report
Short Course on HAZOP and Risk Assessment
UDPS 13
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HAZOP leader - The leader should be independent (i.e. has no responsibility for the process and/or the performance of operations)•Plan sessions and timetable•Control discussion•Limit discussion•Encourage team to draw conclusion•Ensure secretary has time for taking note•Keep team in focus•Encourage imagination of team members•Motivate members•Discourage recriminations•Judge importance issues
Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members
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Checklist for HAZOP LeaderChecklist for HAZOP Leader
Always prepare study program in advance.
Agree on the format or form to be used.
Prepare follow up procedures.
Brief members about HAZOP during first meeting.
Stop the team trying to redesign the process.
HAZOP is a team exercise. Do not let anybody (including the leader himself to dominate).
Short Course on HAZOP and Risk Assessment
UDPS 14
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Process Engineer
• Provide a simple description
• Provide design intention for each process unit
• Provide information on process conditions and design conditions
• Provide a simple description
• Provide design intention for each process unit
• Provide information on process conditions and design conditions
Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members
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Mechanical Design Engineer
• Provide specification details
• Provide vendor package details
• Provide equipment and piping layout information
Instrument Engineer
• Provide details of control philosophy
• Provide interlock and alarm details
• Provide info on shutdown, safety features
Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members
Short Course on HAZOP and Risk Assessment
UDPS 15
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Plant Engineer or Manager• Provide information on compatibility with any existing adjacent plant• Provide details of site utilities and services• Provide (for study on existing plant) any update on maintenance access and
modifications
Shift Operating Engineer or Supervisor• Provide guidance on control instrumentation integrity from an operating
experience view point• Provide (for study on existing plant) information on plant stability at the
specified control parameters• Provide information on experienced operability deviations of hazard
potential
Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members
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Chemist
• Provide details of process chemistry
• Provide details of process hazards (polymerisations, byproducts, corrosion
etc)
Project Engineer
• Provide details of cost and time estimation and also budget constraints.
• Ensure rapid approval if required
Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members
Short Course on HAZOP and Risk Assessment
UDPS 16
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Required informationRequired information
P & IDs
Process flow diagrams
Heat and Material Balances
Layouts
Logic Diagrams
Equipment Data Sheets
Material Hazard Data Sheets
Hazardous area Layouts
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Does any other guideword combine with this parameter to give a meaningful deviation?
Specify the section or stage to be examined
Describe & discuss the step/ operation; determine the design envelope.Develop & record the design intention
From the description and the design intention select a parameter
Combine this parameter with a guideword to develop a meaningful deviation
Seek a possible cause of the deviation and identify the consequences
Evaluate the safeguards and decide if they are adequate of if a changeor further study is needed.
Have all causes of this deviation been considered?
YES
Are there further parameters to consider?
Examination of the steps/ stage is complete
NO
NO
YES
YES
NO
PHASE 2: SELECT A LINE
Record
Divide section into Study linePHASE 1: DIVIDE SECTION
PHASE 3: ANALYSIS
PHASE 4: RECORDING
PHASE 5: REEVALUATE
Sequence for conducting a HAZOP StudySequence for conducting a HAZOP StudyFlow diagram for the HAZOP analysis Flow diagram for the HAZOP analysis –– The parameterThe parameter--first approachfirst approach
Short Course on HAZOP and Risk Assessment
UDPS 17
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Process HAZOP worksheetProcess HAZOP worksheetHazards and Operability Review
Project Name: Date: Page of
Process :
Section: Ref. Drawing:
Item Study node
Process Parameter
Deviations (guide words)
Possible causes
Possible consequences
Action Required
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Guidewords/ KeywordsGuidewords/ KeywordsThe basic HAZOP guide-words are:
Guide-word Meaning Example
No (not, none) None of the design intent is achieved
No flow when production is expected
More (more of, higher) Quantitative increase in a parameter
Higher temperature than desired
Less (less of, lower) Quantitative decrease in a parameter
Lower pressure than normal
As well as (more than) An additional activity occurs Other valves closed at the same time (logic fault or human error)
Part of Only some of the design intention is achieved
Only part of the system is shut down
Reverse Logical opposite of the design intention occurs
Back-flow when the system shuts down
Other than (Other) Complete substitution –another activity takes place
Liquids in the gas piping
Short Course on HAZOP and Risk Assessment
UDPS 18
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Additional guidewordsAdditional guidewords
Guide-word Meaning
Early/ late The timing is different from the intention
Before/ after The step (or part of it) is effected out of sequence
Faster/ slower The step is done/not done with the right timing
Where else Applicable for flows, transfer, sources and destinations
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Process parameterProcess parameter
Process parameter may generally be classified into the following groups:– Physical parameters related to input medium properties– Physical parameters related to input medium conditions– Physical parameters related to system dynamics– Non-physical parameters related to batch type process– Parameters related to system operations
These parameters are not necessarily used in conjunction with guide-words• Instrumentation• Relief• Startup/ shutdown• Maintenance• Safety/ contingency• Sampling
Short Course on HAZOP and Risk Assessment
UDPS 19
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Examples of process parameterExamples of process parameter
Flow Composition pH
Pressure Addition Sequence
Temperature Separation Signal
Mixing Time Start/stop
Stirring Phase Operate
Transfer Speed Maintain
Level Particle size Service
Viscosity Measure Communication
Reaction Control Absorb
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Guidewords + ParameterGuidewords + Parameter
Some examples of combinations of guide-words and parameters:
NO FLOW– Wrong flow path – blockage – incorrect slip plate – incorrectly fitted
return valve – burst pipe – large leak – equipment failure – incorrect pressure differential – isolation in error
MORE FLOW– Increase pumping capacity – increased suction pressure – reduced
delivery head – greater fluid density – exchanger tube leaks – cross connection of systems – control faults
MORE TEMPERATURE– Ambient conditions – failed exchanger tubes – fire situation – cooling
water failure – defective control – internal fires
Short Course on HAZOP and Risk Assessment
UDPS 20
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HAZOP ExerciseHAZOP Exercise
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Case Study Case Study –– Shell & Tube Heat ExchangerShell & Tube Heat Exchanger
Using relevant guide works, perform HAZOP study on shell & tube heat exchanger
Processfluid
Cooling water
Short Course on HAZOP and Risk Assessment
UDPS 21
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HAZOP on Heat Exchanger HAZOP on Heat Exchanger –– Answer 1Answer 1
Guide Word Deviation Causes Consequences Action
Less 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 maintainanceand operator alert
Corrosion Corrosion of tube
Hardness of cooling water
Less cooling and crack of tube
Proper maintainence
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HAZOP on Heat Exchanger HAZOP on Heat Exchanger –– Answer 2Answer 2Guide Word Deviation Causes Consequences 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 lineInstall 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 (whether it is crucial have to check?)
CONTAMINATION
Process fluid contamination
Contamination in cooling water
Outlet temperature too low
Proper maintenance and operator alert