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
Features of HAZOP Study
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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
Features of HAZOP Study
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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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Guide Word Deviation Causes Consequences
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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Guide 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 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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