cf lecture 12 hazard identification
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Hazard IdentificationWhy? To identify hazards so that they can be
eliminated or controlled.
How? Using a number of available procedures.
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P-36
platform on
transport
barge
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Other examples of accidents due to
undetected hazards. Titanic 1912. Bulkheads not full height.
Water flooded into adjacent compartments.
Alexander Keilland 1980. Undetectedcracks in bracing member. Leg detached
from rig which capsized.
Esso Longford 1998. No HAZOP. Heat
exchanger failed due to low temperatures.
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How many hazards can you identify?
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Approach to all Hazard Identification methods
Identify process hazards
Review previous incidents
Analyze engineering and administrative controls and consequencesof control failures
Consider facility location
Address human factors
Evaluate effects of incidents on employees
Decide when action items are warranted
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Brainstorming
Rules Postpone and withhold your judgement of ideas.
Encourage wild and exaggerated ideas.
Quantity counts at this stage, not quality.
Build on the ideas put forward by others.
Every person and every idea has equal worth.
By its very nature a brainstorming
session cannot be structured, but it
can be guided.
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HAZARD IDENTIFICATION METHODS
Check List
What If
Hazid Hazop
Task Analysis
Fault Tree Analysis Failure Modes & Effects Analysis
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Safety Analysis
QualitativeCheck Lists
What If Reviews
Hazop Reviews
QuantitativeEvent Trees
Fault TreesFailure Mode and Effects Analysis (FMEA)
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Process Hazard Identification
Selection of the most appropriate methods for each facility or processand provide the rationale for their selections.
Sometimes a combination of methods may be most appropriate.
Depends on many factors including the size and complexity of theprocess and existing knowledge of the process.
All Hazard Identification methods are subject to certain limitations.
Hazard Analysis depends on good judgement, therefore assumptionsmade must be documented, understood, and retained for future
hazard reviews.
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Consider each situation to be unique
Each may require a different approach
Each is dependant upon process complexity
Increasing Expertise Required
Obvious low hazard
or simple process
Obvious high hazard or
complicated process
Supervisor Expert Team
Hazard Identification
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Checklist Analysis
A checklist analysis is used to verify the status of a system.
The checklist analysis method is versatile, easy to use and can beapplied at any stage in the life of a process. It is primarily used toindicate compliance with standards and practices. It is also a cost-effective way to identify common and customarily recognizedhazards.
Checklists also provide a common basis for management review ofassessments.
Many organizations use standard checklists to control thedevelopment of a process or an entire project from initial designthrough decommissioning.
The completed checklist must be approved by all relevant staffmembers and managers before a project can move from one stageto the next.
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Process Hazards Checklist Analysis
Storage. Storage tanks, dykes, emergency valves, inspection, maintenance,procedures, specifications, limitations
Materials Handling. Pumps, conveyors, ducts, piping, procedures
Process Equipment and Systems. Procedures, conformance, loss of utilities,vessels, relief devices, hazards, electrical, ignition sources, compatibility
Personnel Protection. Protection, ventilation, exposure, hazards manual,environmental
Controls and Emergency Devices. Controls, calibration, inspection, alarms,interlocks, relief devices, emergencies, process isolation
Waste Disposal. Ditches, vents, characteristics,
Sampling. Sample points, procedures, sample analysis
Maintenance. Decontamination, vessel opening, procedures
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Cooling Water Chlorination System
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MATERIAL
Do a l l ra w m a t e ri a l s co n t i n u e t o co n f o rm t o o ri g i n a l sp e ci f i ca t i o n s? Yes. The drums are ordered with the same chlorine specification used
since startup.
Is e a ch re ce ip t o f m a t eri a l ch e cke d ? Yes. The supplier once sent acylinder of phosgene.
Since then, a test is performed by the maintenance staff. In addition, thefusible plugs are inspected for evidence of leakage, before a cylinderis hooked up.
Do e s t h e o p e ra t i n g s t a f f h a ve a cce ss t o M a t eri a l S af e t y Da t a Sheets? Yes. All staff are familiar with the process chemistry,including the hazards of Chlorine.
I s f i re f i g h t i n g a n d sa f e t y e q u i p m e n t p ro p e rl y l o ca t e d a n d m a i n t a i n e d ? Yes. This system is on a concrete building roof.Because there are no flammable materials involved in this system, if afire occurs, there will be no special effort by fire fighting crews toconcentrate on the roof area.
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EQUIPMENT
H a s a ll e q u i p m e n t b e en i n s p e c t e d a s s c h e d u l e d ? Yes. The maintenancepersonnel have inspected the equipment in the process area according tocompany inspection standards.
H a v e p r e s s u r e r e l ie f v a l v es b e e n i n s p e c t ed a s s c h e d u l e d ? Yes.
H a v e r u p t u r e d i s k s b e e n i n s p e c t e d ( fo r h a v i n g b l o w n ) as s c h e d u l e d ? Notapplicable.
A r e t he pr oper maint enance mat er ials ( par t s, et c. ) avai lable? Yes. Theyinclude spare pigtails for the supply cylinders, as well as a rotameter and apressure check valve. Other items must be ordered.
Is t h e r e a n e m e r g e n c y c y l i n d e r c a p p i n g k i t ? Yes.
PROCEDURES
A r e t h e o p e r at i n g p r o c e d u r e s c u r r e n t ? Yes.
A r e t h e o p e r a t o r s f o l l o w i n g t h e o p e r a t i n g p r o c e d u r e s ? No. It is reported thatsome staff do not always check the cylinder's fusible plugs for leaks. Staffshould be re-reminded of this procedural item and its importance.
A r e n e w o p e r at i n g s t a f f t ra i n ed p r o p e r l y ? Yes. Training includes a review ofthe Hazard Analysis for this process and familiarization with MSDSs.
H o w a r e c o m m u n i c a t i o n s h a n d l e d a t s h i f t c h a n g e ? There are relatively fewopen items at the end of a shift. The chlorine cylinders need to be changedonly about once every 45 days. If an empty chlorine cylinder needs replaced,it has proven to be easy to schedule the change during a shift.
Is h o u s e k e ep i n g a c c e p t ab l e ? Yes.
A r e s a f e w o r k p e r m i t s b e i n g u s e d ? Yes.
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Does not address new processes, equipment, etc.
May miss issues not covered by lists
Past data might not contain infrequent, high consequence
accident
Encourage a tick off mentality
Does not deal effectively with hazards that arise from
interactions
Checklist Limitations
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Later model with round windows
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What If Analysis
What-if analysis is to identify hazards,
hazardous situations, or specific
accident events that could produce an
undesirable consequence.
What-if analysis involves the examination
of possible deviations from the design,
construction, modification, or operatingintent of a process.
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Approx Time Requirements
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Advantages of What if analysis
It can be accomplished with a relatively low skill level.
The typical What if review is a brainstorming session, allsorts of topics may be randomly addressed as they arethought up. Combined with a checklist format, thereview may become simple to answer.
It is fast to implement, compared to other qualitative
techniques. What if review is a direct question methodpossibly from a standardized check list from whichquestions can be easily and rapidly addressed.
It can analyse a combination of failures. The option ofaddressing continuing sequential failures can be
investigated.
It is flexible. It is readily adaptable to any type ofprocess and questions can focus on specific potentialfailures.
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Limitations of What if technique
It is based on experience. A what if analysis cannot berelied upon for identifying unrecognized hazards. Areview team may fail to investigate deep enough intothe process with which they have become superficiallyfamiliar. Unless the review team asks the rightquestions, hazards may not be identified.
It is not systematic. It is considered a brainstormingsession. Personnel familiar with the facility discussaspects in a random fashion whatever comes to mind.
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Combines the creative, brainstorming feature of
what if analysis and the systematic features of
the checklist analysis to try and overcome the
random approach of What If.
What If /Checklist
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HAZID (HAZard IDentification)
A process where a list of hazards and
guidewords is applied to a facility or
activity in a systematic manner.
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HAZID
Suitable for application during concept selection, and equally
for review of basic development concepts when the following
level of information is normally available:
operations philosophy sparing and maintenance philosophy
process flow schemes
preliminary layouts
fire and explosion strategies.
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Hazards Guidewords
Release GasLiquid
Condensate
Other
Fire Fuel sourceIgnition
Relief
Smoke & gas ingress
Explosion FuelConfinement
Impact LiftingMaintenance
Mechanical failure
Structural Failure Primary structuresTemporary structures
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Hazards Guidewords
Environmental VolatilesLiquids
Solids
Chemical TypesHandling
Protection
Logistic Aviation
MarineOther
Materials CorrosionErosion
Climatic EarthquakeExtreme weather
Occupational OperationalDiving
Transport
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HAZID
Divide the item under consideration into nodes, whichare manageable sections, with clearly defined limits.
Apply the first guideword and ask how could this
happen?
Determine in what manner the hazard might be realised.
What would be the consequence of this?
List any existing safeguards or precautions.(Preventive
or control measures)
List any areas for discussion or any actions which need
to be taken.Record everything, drawings used, team members,
dates.
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HAZID Worksheet
HAZARD PHASE CAUSE EFFECT/ESCALATION
PREVENT CONTROL DISCUSSION ACTION
Loss ofcontainment
Production Leak of processgas containingH2S
Toxic gas cloud.Risk topersonnel onplatform
The amount ofprocessequipment onthe platform isbeing kept to aminimum, withprocessing ofthe gas beingperformedonshore.
Platform is designedso that the prevalentwind direction isaway from themuster andevacuation areas.
Breathing apparatusis available on theplatform
Saver sets will beprovided to allpersonnel (typicallyup to 15 minutesprotection againstH2S)
Arrangementsfor changingfrom saversets to BA sets
are not clear.
Command andcontrol with
personnelwearing BAwill be difficult.
Action 001: Confirm thecommand and control strategywith regard to H2S and wearingBA.
Action 002: Develop anevacuation strategy that issuitable for a sour gasenvironment.
Action 003: Develop anintervention schedule and
ensure that intervention is keptto an absolute minimum bykeeping the amount of processequipment to a minimum.
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HAZOP Objectives
To identify the causes of all deviations or
changes from the design intent
To determine all major hazards and
operability problems associated with these
deviations
To decide whether action is required to
control the hazard or the operability problem
To ensure that the actions decided upon are
implemented and documented
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Formal procedure for identifying hazards
Basic idea generate a list of all the ways in which
process failures can occur
Determine what may cause each failure and what the
results might be
Recommend actions to avoid each failure
Not quantitative no trade off between risk and
consequences
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Coarse Hazop - Early study to identify basic flaws indesign which would be costly to correct later
Main Hazop - Primary vehicle for identification of
hazards, effects and operability problems
Final Hazop - Coverage of systems not sufficiently
developed for the Main Hazop
Procedural Hazop - Identification of hazards and
operability problems arising from procedures such as
commissioning, maintenance and other non-
continuous procedures.
HAZOP types
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HazidCoarse
Hazop
Main
Hazop
Procedures
Final Hazop
Commissioning
Identification Phase Definition Phase
Prospective Project Front End Engineering
Execution Phase
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HAZOP Leader
HAZOP SecretaryHAZOP Leader Specialists(as required)
Process Engineer
Instrument Engineer
Operations Representative
Maintenance Engineer
Pipeline Engineer
Metallurgist
others
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Preparatory Work
Assemble the data
Understand the subject
Subdivide the plant and plan the sequence
Mark up the drawings Devise list of appropriate keywords
Prepare table headings and an agenda
Prepare a timetable
Select the team
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Hazop study
Full size Piping & Instrumentation Diagram
(P&ID) displayed. Team members are provided
with individual reduced size P&ID copies
Introductory talk and brief description of thetechnique are given by the Hazop chairman.
A plant description is provided usually by the
process engineer, summarizing the processing
facilities, including an account of the function ofeach equipment item.
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The accuracy of the drawings and other data used
as the basis for the study
Technical skills and insights of the team
Ability of the team to use as an approach as an aid
to their imagination in visualising deviation, causes
and consequences
Ability of team to maintain sense of proportion
Key aspects for success of Hazop
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Node Identification
Divide the facility into process systems and
subsystems
Follow the process flow of the system understudy
Isolate subsystems into major components which
achieve a single objective
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Parameters
FLOW
PRESSURE
TEMPERATURE
LEVEL
PHASE
COMPOSITION
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Guidewords
p
p
p
p
p
p
FLOW
Analysis based on appropriate
operations identified by the team
PRESSURE
TEMPERATURE
LEVEL
PHASE
COMPOSITION
(specific component)
NO
MORELESS
ASWELLAS
PA
RTOF
REVERSE
OTHER
THAN
Typical Operations:Isolation
Maintenance
Start-up
Shutdown
Blowdown
Parameters
p = possible
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Hazop study
Select the appropriate NODE
Apply the PARAMETER
Apply the GUIDE WORD (orDEVIATION)
Agree credibility of deviation
Determine the potential CAUSES of the deviation
Assess the PROTECTION provided against thedeviation and its consequences
Agree a RECOMMENDATION for action or further
consideration to the problem.
Reiterate above steps for other GUIDE WORDS
Reiterate above steps for other process
PARAMETERS
Reiterate above steps for other NODES in review
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Maintenance
Utility failure
Start-up
Normal shut down
Emergency shut down
Operational phases
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Equipment Failure
Operational Errors
External Events
Product Deviations
Possible CAUSES
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CREDIBLE SCENARIOS
A single human error with or without established operating
instructions
A single instrument or mechanical failure
A single failure coupled with a single instrument or
mechanical failure
NON CREDIBLE SCENARIOSSimultaneous failure of two independent instrument or
mechanical systems
Failure of both the primary and secondary relief device to
operate as designed
Immediate change of process characteristicsMassive impact from foreign object
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RECOMMENDATIONS
Modify the design
Add an alarm
Add an interlockDevelop or change procedure
Review the design
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Documentation
Summary reportHAZOP worksheets
List of proposed actions
The report is updated when all engineering and some
procedural actions are completed.
At the end of the project, a final report is issued
including
HAZOP Procedure
HAZOP Follow-up ReportList of all actions with status (completed, in progress
etc)
Complete set of P&IDs as used in the HAZOP study
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HAZOP FORM
Unit: Fired Heater
Node: Feed pipe Parameter: Flow
Location (line or vessel) Process variablesor procedure (start up)
Guide Word Deviation Cause Consequence Action
Select from
official list of
words to ensure
systematic
consideration ofpossibilities
applying guide
word to this
parameter
process
engineering
process
engineering
preliminary result
which should be
reconsidered when
time is available
no no feed flow 1. feed pump stops damage to pipes inradiant section,
possible pipefailure
1. automaticstartup of backup
pump on low feedpressure
fuel
air
feed
product
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2. feed valve
closed
2. fail open valve
3. feed flow meter
indicates false high
flow (controllercloses valve)
3. redundant flow
meters
4. pipe blockage 4. a) test flow
before startup
4. b) place filter in
pipe
5. Catastrophic
failure of pipe
5.a) damage to
pipes in radiantsection
b) pollution and
hazard for oil
release to plant
environment
Install remotely
activated blockvalves at feed
tanks to allow
operators to stop
flow
For 1-5, SIS to
stop fuel flow onlow feed flow,
using separate feed
flow sensor
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Advantages of Hazop
It uses a systematic and logical approach. It hasspecific guideword listing and the process underreview is subdivided into small sections for analysis
It can analyse a combination of failures. The optionof addressing continuing sequential failures can be
investigated to the final outcome.
It provides an insight into operability features.Operation control methods are fully investigated forpotential deviating conditions. Operators presentcan readily deduct what hazards may be present at
the facility.
Li it ti f H t h i
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Limitations of Hazop technique Require well defined system
Time consuming. It may be slower than other methods.The team leader follows a standard format with specialguidewords and deviations that need to be addressed.Because of standardized listings some unimportantissues may be addressed in some portions of thesystem under review.
Provide no numeric ranking of hazards unless coupledwith a risk ranking scheme
Requires trained personnel with moderate level of skillto conduct. The review is thorough and systematicwhich has to be implemented in a proper fashion andaccurately recorded. A specialized leader is used toguide the review team during the process.
Focus on one-event failures
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TASK ANALYSIS
Systematic examination of a task to be
performed, listing all the ways in which it
might be performed in an unsafe manner.Introduction of safeguards and controls to
prevent or minimise the consequences of
a failure.
Sometimes called a job safety analysis.
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Failure Mode Effect Analysis
A FMEA is used to examine each potential failuremode of a process to determine the effects
of the failure on the system.
A failure mode is the symptom, condition, or
fashion in which hardware fails.
It may be identified as a loss of function, apremature function (function without demand), anout-of-tolerance condition, or a physicalcharacteristic, such as a leak, observed during
inspection. The effect of a failure mode isdetermined by the system's response to thefailure.
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A FMEA has three steps:
defining the process,
performing the analysis, and
documenting the results.
.
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Application of FMEA
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Risk Assessment
Occasional
Seldom
MajorMinor
High High
High
Medium
Medium
Medium
Low
LowLow
Frequent
Substantial
Risk Prioritisation Matrix
Severity
Likelihood
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Personnel Risk Ranking MatrixLevel 5
Level 4
Level 3
Level 2
Level 1
A B C D E
Increasing likelihood
Increasin
gconsequenc
e
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Severity or Consequence
Level 5 - Multiple Fatalities
Level 4 - Single Fatality, Multiple Injuries
Level 3 - Major Injury Level 2 - Minor Injury
Level 1 - No Injury, Near Miss
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Consequence IncreasingLikelihood
A B C D E
Rating AccidentSeverity
Neverheard ofinindustry
Heard ofinindustry
Incidenthasoccurredin our company
Happensseveralper yearin ourcompany
Happensseveraltimes peryear inlocation
0 NoInjury
1 SlightInjury
2 Minor Injury
3 Major Injury
4 SingleFatality
5 MultipleFatalities
IncreasingRisk
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Swiss Cheese theory
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Are more layers safer?
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Layers of Protection Analysis (LOPA)
A risk assessment tool, often used after a HAZOP, todetermine if protective measures are sufficiently robust, orneed augmenting.
Looks at the various protective methods, or layers, such asInherent Safe Design, engineering controls, administrativecontrols, response systems etc These should be
independent from each other, and are called IndependentProtective Layers (IPL).
Develop order of magnitude estimates for likelihood andconsequence severities.
Determine how much protection each IPL provides, for aparticular fault scenario, and what combination is needed toprovide adequate contingency.
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IPL1 IPL2 IPL3
Safe outcome
Undesired but
tolerable outcome
Undesired but
tolerable outcome
Consequences in
excess of risk criteria
Success
Success
Success
Failure
Failure
Failure
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