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Calgary Tel 1-403-221-8077 Fax 1-403-221-8072E-mail: [email protected] Website: www.seal.ab.ca
PROCESS HAZARDS ANALYSIS
LEADERSHIP TRAINING
NPC TRAINING PROGRAM
STUDENT HANDOUT
Presented byMarcel Leal-Valias
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Table of Contents
COURSE OBJECTIVES.................................................................................................. 1
COURSE OBJECTIVES ....................................................................................................... 1OVERVIEW OF PHA ......................................................................................................... 2PHA IN ANUTSHELL........................................................................................................ 3HISTORY OF PHA............................................................................................................. 4
QUANTITATIVE & QUALITATIVE HAZARD ANALYSIS.................................... 5
QUANTITATIVE AND QUALITATIVE HAZARD ANALYSIS OVERVIEW ................................ 5PHA AND RISKANALYSIS COMPARED ............................................................................ 6
OVERVIEW OF HEALTH, SAFETY & ENVIRONMENT HAZARD
MANAGEMENT .............................................................................................................. 7
SAFETY MANAGEMENT SYSTEMS REVISITED BY HAZARDS ANALYSIS ........................... 9
ELEMENTS OF FACILITY RISK .............................................................................. 13
PROCESS ACCIDENTS ..................................................................................................... 14PROCESS RISKREDUCTION STRATEGIES........................................................................ 15HUMAN FACTORS IN FACILITY RISK.............................................................................. 15
Factors Influencing Human Performance ................................................................ 17Human Error In Accident Causation........................................................................ 18Human Error Risk Reduction Checklist at Different Levels of Interaction.............. 21
SITING ISSUES IN FACILITY RISK.................................................................................... 22ENVIRONMENTAL ISSUES IN FACILITY RISK................................................................... 23
PHA TEAMS................................................................................................................... 25
SIZE OF PHATEAM ....................................................................................................... 25WHY A TEAM APPROACH?............................................................................................. 25RESPONSIBILITY OF GROUP PARTICIPANTS IN PHAS ..................................................... 27THINKING SKILLS REQUIRED OF PARTICIPANTS IN PHAS .............................................. 27
PHA METHODOLOGIES ............................................................................................ 30
VIDEOPROCESS HAZARDS ANALYSIS......................................................................... 30GENERAL PHAPROCEDURE FLOW CHART .................................................................... 31OBJECTIVES OF A GOOD PHASTUDY ............................................................................ 32PROCESS SAFETY INFORMATION FORHAZARDS ANALYSIS............................................ 32VIDEOPROCESS SAFETY INFORMATION...................................................................... 32METHODOLOGIES OVERVIEW ........................................................................................ 35
HAZard and OPerability Analysis (HAZOP) ........................................................... 35Preliminary Hazards Analysis.................................................................................. 44Checklist Analysis ..................................................................................................... 47What-If Analysis........................................................................................................ 49What-If/Checklist Analysis........................................................................................ 51Failure Modes and Effects Analysis (FMEA)........................................................... 53
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Other PHA Methodologies Reserved for Specific Safety Concerns.......................... 57ADVANTAGES AND DISADVANTAGES OF PHAMETHODOLOGIES .................................. 58LIMITATIONS OF PHA.................................................................................................... 59
METHODOLOGY SELECTION CRITERIA ............................................................ 60
FACTORS TO CONSIDERWHEN SELECTING THEAPPROPRIATE PHAMETHODOLOGY.. 60Purpose of Study ....................................................................................................... 60Type of Results Required .......................................................................................... 61Type of Information Available .................................................................................. 61Time Frame for Completion of Study........................................................................ 61Development Phase of the Facility ........................................................................... 62Relative Risks Associated with Chemicals, Process and/or Facility Location......... 64PHA Team Experience Level .................................................................................... 65Operating History (Past Incidents)........................................................................... 65Resource Availability and Management/Leader Preference .................................... 65
METHODOLOGY SELECTION FLOW CHART .................................................................... 66COST BENEFIT CONSIDERATIONS................................................................................... 67
DOCUMENTATION ISSUES....................................................................................... 68
DOCUMENTATION FORDECISION MAKING .................................................................... 68DOCUMENTATION FORFUTURE REFERENCE .................................................................. 68WORKSHEET REPORT..................................................................................................... 69COMPLETED REPORTS.................................................................................................... 70
Usual Format for PHA Report.................................................................................. 71LEGAL ISSUES (DUE DILIGENCE)................................................................................ 72
PHA LEADERSHIP....................................................................................................... 73
PHAFACILITATION SKILLS ........................................................................................... 73
TEAM LEADERQUALIFICATIONS ................................................................................... 73PHALEADERSHIP RESPONSIBILITIES............................................................................. 74
Causes and Solutions for PHA Quality Problems .................................................... 77PHAGROUP DYNAMICS ................................................................................................ 78GETTING THE BEST FROM YOURTEAM ......................................................................... 80
PHA WORKSHOP (HAZOP & WHAT-IF)................................................................ 84
DEFINING SCOPE AND OBJECTIVE OF PHAS................................................................... 84ESTIMATING TIME FORPHAS AND PLANNING SCHEDULE ............................................. 87QUALITATIVE RISKRANKING MATRIX FORPHAS......................................................... 89FIRST MEETING.............................................................................................................. 93
DOCUMENTING THE PHAWORKSHEET ......................................................................... 94CREDIBILITY OF CAUSES................................................................................................ 95ACCIDENT CAUSES CATEGORIES TO BE CONSIDERED BY PHATEAM .......................... 97PHAFOLLOW-UP .......................................................................................................... 98
PHA WORKSHOP DRAWING RESOURCES .......................................................... 99
APPENDIX.................................................................................................................... 101
GLOSSARY OF PHATERMS.......................................................................................... 101
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COMMON HAZOPTERMINOLOGY............................................................................... 108SIMPLIFIED CHECKLIST FORHAZARD ANALYSIS ......................................................... 110SAMPLE HAZARD CHECKLIST ...................................................................................... 114SAMPLE MATERIAL INCOMPATIBILITY INDEX.............................................................. 118LIST OF HIGHLY HAZARDOUS CHEMICALS,TOXINS AND REACTIVES .......................... 119
METHODOLOGY SELECTION AND/ORPRIORITY ORDERING WORKSHEET FORCONDUCTING PHAS .................................................................................................... 124ARTICLE....................................................................................................................... 131
Extend HAZOP to Computer Systems ................................................................ 131ARTICLE....................................................................................................................... 132
Culture................................................................................................................ 132STANDARDS ................................................................................................................. 133
Management of Process Hazards....................................................................... 133STANDARDS ................................................................................................................. 134
OSHA 29 CFR PART 1910................................................................................. 134
READING ENGINEERING DRAWINGS ................................................................ 135
TYPES OF ENGINEERING DRAWINGS USED IN PHASTUDIES ....................................... 135OVERVIEW OF READING P&IDS .................................................................................. 136
Valve Markings ....................................................................................................... 136Examples of P&ID Abbreviations........................................................................... 137
ENGINEERING DRAWING INFORMATION....................................................................... 139Function Blocks ...................................................................................................... 140Reference Symbol Sheets......................................................................................... 142General Symbols ..................................................................................................... 143Instrument/Process Line Symbols........................................................................... 147Valve Body Symbols................................................................................................ 148Self Actuated Valves................................................................................................ 150Flow Rate Symbols.................................................................................................. 152Actuator Symbols .................................................................................................... 154Typical Letter Combinations................................................................................... 155
GENERAL REFERENCES......................................................................................... 156
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CCOOUURRSSEE OOBBJJEECCTTIIVVEESS
Course Objectives
The objectives for this course are:
To build an understanding of the concepts of Process Hazards Analysis (PHA)
and its role in Health, Safety and Environment management.
To provide a basic understanding of all the major hazard identification techniques
and when each should be used.
To provide an understanding of the responsibilities involved in PHA leadership.
To provide basic skills and practice in the use of the What-If and HAZOP
techniques.
To provide training in the use of software as a tool in the facilitation of PHA.
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Overview of PHA
A PHA is a systematic multidisciplinary team study. It focuses on identifying and
analysing the significance of potential process hazards and on making initial
recommendations for eliminating and/or reducing the consequences of potential
incident/accidents.
A PHA is the foundation of any Process Safety Management Program.
A PHA is interested in the potential causes, likelihood and consequences of
process incidents.
A PHA works by combining the experience, knowledge and intuitive
imaginations of expert team members with a selected analytical methodology.
A PHA provides companies with the information necessary to make operating
decisions, to help improve safety, and to manage the risk of operations.
Various hazard identification methodologies provide flexibility according to time
scope and objectives of study.
A PHA should be conducted several times during a facilitys design, construction
and operating life cycle.
Some methodologies not only identify hazards, but also operability problems.
A PHA assigns qualitative likelihood and severity ratings from which a relative
risk ranking can be estimated.
A PHA identifies high level hazards for possible further quantitative risk analysis.
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PHA in a Nutshell
FOUNDATION FOR PROCESS HAZARDS ANALYSIS
Historical
Experience
PHA
Methodology
Kno
and I
PROCESS HAZARDS ANALYSIS
What can gowrong?
How likely is
it?
What are
consequen
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History of PHA
HAZOP, the first formal PHA, was developed in the UK at ICI over 30 years ago.
Other methodologies have followed as requirements for less comprehensive and
time consuming reviews have emerged.
The occurrence of major industrial accidents and the subsequent forceful safety
and environmental legislation throughout the world has led to Process Safety
Management (PSM) or Process Hazards Management becoming an industry
standard.
Companies have become increasingly aware that operating a safer facility leads to
a more profitable business and that, in the long run, safety is in the best financial
interest.
Development of sophisticated software to aid in the sometimes tedious task of
PHA has lead to its adoption throughout the process chemical industry.
PHA was legislated (1992) in the USA as part of OSHA CFR 29, Part 1910.
PHA is part of American Petroleum Institute (API) Recommended Practice 750,
1990, which stands as the recommended standard for Canadian process industries.
OSHA 29 CFR, British Standards 8800 and Norwegian regulations have become
the world standards.
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QQUUAANNTTIITTAATTIIVVEE && QQUUAALLIITTAATTIIVVEE HHAAZZAARRDD AANNAALLYYSSIISS
Quantitative and Qualitative Hazard Analysis Overview
Safety is Good Business Both qualitative and quantitative hazard analyses are important in identifying and
analysing risk.
It is a given that money properly spent on safety increases profitability through
fewer injuries and reduced lost time, and through reduced property and production
losses.
However, too much money can be spent on safety and the benefits can be
outweighed by the cost. For instance, if the predicted expenditure to remove an
identified hazard is very high, it will be necessary to statistically quantify its
probability and the scope of its consequence to decide how it can be best
minimized.
PHA is the initial predictive identification of potential hazards.
RISK ANALYSIS provides a statistically based quantitative assessment of the
probability and consequence of major hazards identified in a PHA.
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PHA and Risk Analysis Compared
PHA RISK ANALYSIS
Initial predictive identification of all
potential hazards - estimates likelihoodand severity, suggests improvements
USE ON EVERY PROJECT- at everystagefrom concept throughdecommissioning
QUALITATIVE- based on the experience,knowledge and creative thinking ofworkers involved in the process
MULTIDISCIPLINARY TEAM
Several methodologies available
What-if
What-if/Checklist HAZOP
FMEA
Preliminary Hazards Analysis
Subsequent assessment of major hazards
only statistically based probability /consequence hazard assessment
SELECTIVE- if the potential exists for acatastrophic accident or if no easy andobvious solution to identified hazard isevident
QUANTITATIVE- requires extensivestatistical data and specialized expertise very costly
ONE OR TWO SPECIALLY TRAINED
PEOPLE
Also called:
Hazan
Risk Assessment Probabilistic Risk Assessment (PRA)
Quantitative Risk Assessment (QRA)
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OOVVEERRVVIIEEWW OOFF HHEEAALLTTHH,, SSAAFFEETTYY && EENNVVIIRROONNMMEENNTT HHAAZZAARRDD
Health, Safety & Environment
Cost SavingsQuality Production
Customer Satisfaction
Process Review
ManagementCommitment
Hazard C
Hiring &Health
Monitoring
Inspections
Accident /Incidents
Hazard Assessment
Off-The-Job Safety
EmergencyPreparedness
& Response
Com
HSE SteeringCommittee
HazardousMaterials
PreventativeMaintenance
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Safety Management Systems Revisited By Hazards Analysis
Hazard identification and assessment has to be the starting point for successful HSE
management. The information gained from a PHA about potential hazards, is essential to
any HSE Management Program. Human, process, equipment, environmental and
production hazards can be identified and the information used to develop and fine-tune
all the component systems of a Safety Management Program.
Let us revisit the HSE Management System introduced in the introductory session, this
time reflecting on the pivotal role that PHA plays in each component.
Management Commitment
provides the essential information for risk management decision making
can pinpoint gaps in management and administrative controls
demonstrates management commitment to the safety of personnel boosting
employeemorale
Hazards Identification and Assessment
identifies a wide range of hazards to people, process, structures, equipment, and
the environment, e.g. chemical, biological, ergonomic, radiation, etc.
identifies actual and hidden potential hazards
allows hazards to be prioritised according to risk ranking making management
decision making easier
identifies high risk hazards requiring further quantitative analysis
can provide recommendations for mitigating consequences of accidents
highlights opportunities for improving operability
Hazard Controls
Rules & Procedures
design layout information can identify design errors and highlight opportunities
for debottlenecking and improving operability.
identifies a need for formal operating, maintenance and emergency procedures
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highlights weaknesses in existing procedures
can be adapted to perform Job Hazard Assessments and Critical Task Analyses
identifies the need for a refresher training schedule
Management of Change
identifies design or material errors of the proposed change
follows the effect of the proposed change on the rest of the process and facility
identifies where procedures are missing and need to be improved
identifies where additional training may be required
identifies the health, safety and environmental considerations of proposed changes
can provide initial recommendations for mitigating consequences of accidents
Contractor Management
identifies requirement for procedures and training
identifies potentially hazardous interaction with the operation
Training - Management & Employees
trains management and PHA participants in the hidden hazards of their workplace
highlights gaps and deficiencies in training
Communication (Record Keeping)
highlights gaps and deficiencies in communication
provides reported and stored information about hazards and gaps in Safety
Management Systems
provides recorded system for resolution of HAZOP recommendations
identifies the hazard potential of proposed changes
provides the opportunity to prove due diligence
Inspections
provides a paper trail for resolution of recommendations for hazard reduction
highlights gaps and deficiencies in HSE Management
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Hazardous Materials
identifies potential immediate and long term health concerns
identifies potential chemical interaction hazards
identifies gaps in existing precautionary procedures
can provide recommendations for mitigating consequences of accidents
Hiring & Health Monitoring
identifies areas where additional health monitoring may be required
Emergency Preparedness & Response
identifies potential types of emergencies and harm
identifies gaps and deficiencies in the Emergency Response Plan
Accident/Incident Investigation
provides a paper trail for accident/incident investigation
provides valuable past incident information for a PHA - highlights potential
hazards
HSE Steering Committee
identifies workplace hazards
identifies need for additional controls
Preventive Maintenance
identifies areas and equipment requiring regular preventive maintenance
trains maintenance personnel in the process and its potential hazards
Off The Job Safety
assists participants with general safety awareness
Process Review/Audit
provides the basis for an audit
broadly identifies the actual or potential gaps in the overall Safety Management
System
provides paper trail
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Conclusion
Proactively taking care of the safety of people, production, equipment and the
environment makes good economic sense. The way to start to take care of safety is by
identifying and assessing the actual and potential hazards in the facility and by putting a
well-planned system in place to manage them.
If you do not know what can go wrong, or how often it is likely to go wrong and what the
consequences may be, it is impossible to plan or operate a safety system effectively.
Often, time and money can be spent reacting to accidents and near misses without
really getting very far in reducing the existing and potential hazards and their associated
visible and hidden costs.
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EELLEEMMEENNTTSS OOFF FFAACCIILLIITTYY RRIISSKK
Hazard potential arises from any combination of risk elements, such as process, material,
siting, environment and human interaction, and exists at all levels throughout a facility
lifecycle.
To identify ways to eliminate or reduce the frequency and consequences of process
accidents, it is essential to understand the breadth of hazard potential in a facility. Process
hazards are always a combination of hazardous materials and the conditions under which
they are handled. However, it usually takes a sequence of events to create an accident
outcome. The important thing to remember as a PHA facilitator or participant is that each
event in the sequence presents an opportunity to avert the accident or to mitigate the
severity of its outcome. PHAs can play an important educational role in helping workers
participating in them to understand potential accident sequences in their facility and see
the significance of failure of defenses at any level.
Process accidents are rarely the result of isolated events; they are usually the result of a
sequence of failures or errors.
Initiating events are the first events in an accident sequence, the event or action that
sets off a chain reaction. Sometimes the initiating event may be the only event if there
is no built in protection against it or the event is so severe that existing protection is
overwhelmed by the event.
Propagating events are the secondary events that link an initiating event to an
accident outcome. These events are the responses that engineered safety features and
administrative controls make when the initiating event occurs. Usually these events
can be correlated to equipment failure, human error, inadequate safety defences,
inadequate administrative controls or unusual external conditions.
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Process Accidents
HAZARDOUS MATERIALS + PROCESS CONDITIONS
INITIATING EVENTS
Design ErrorsManagement System FailuresHuman ErrorsExternal Events
PROPAGATING EVENTS
Equipment FailuresSafety System FailuresIgnition SourcesManagement System FailuresHuman ErrorsExternal Contributions (e.g. theweather)
ACCIDENT OUTCOMES
EmissionsFiresExplosions
Projectiles
ACCIDENT EFFECTS
Toxic (acute & chronic)ThermalOverpressure
RadiationContamination
DAMAGE ASSESSMENTS
EmployeesSurrounding CommunityEnvironment
ProductionCompany AssetsCompany ReputationCompany Liability
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Process Risk Reduction Strategies
Risk reduction strategies are built-in defenses and appropriate responses to initiatingevents that avert an incident or mitigate the severity of outcome.
Operator Control Systems Alarms/early warning
Control system response
Manual and automatic ESD Fire/gas detection system
Operating Safety Systems Relief valves
Depressurization systems
Isolation systems High reliability trips
Back-up systems
Specially designed structures
Mitigation Systems
Dikes and drainage Flares
Fire protection systems
Explosion vents
Toxic gas absorption
Ventilation systems
Emergency Plans
Sirens/warnings Emergency procedures
Personnel safety equipment
Safe shelters
Escape and evacuation
Management
Commitment to Safety ManagementProcess Safety Information availableand up to date.
Training Systems
Operations
Contractors Procedures
Source: Adapted from Table 1.3, Guidelines for Hazard Evaluation Procedures, AIChE, New York, 1992.
Human Factors in Facility Risk
Human error is seen as the incompatibility of task demands and human emotional, mental
and physical capabilities. Human errorhas been the major cause of almost all
catastrophic accidents in the chemical process industry and has an ultimate impact on
profitability through losses and lower quality product. Human error can be reduced if the
workplace culture and the tasks within it are designed with consideration for the needs
and capabilities of those who will interact with it.
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The PHA objective, in considering human factors in facility risk, is to look at all aspects
of potential human interaction with a process to predict what could possibly happen.
When human causes are taken into account, hazards that appear unlikely on a hardware
level may significantly increase in likelihood.
SCOPE OF HUMAN ERROR
HUMAN FAILURE
ERRORS VIOLATIONS
Deliberate actions Different from those prescribed
Carries known associated risks
Ignores operational procedures
Violation errors occur because of aperception of lack of relevance, timepressure or laziness.
Competency exists
Intentions are correct
Slips occur while carryingout habitual, routine, skillbased activity automaticpilot syndrome
Incorrect intention
Inadequate knowledge
Incorrect information processing
Inadequate training
Mistakes occur because of poor attitude, incorrectassumptions or incorrect tunnel vision application ofrules.
SLIPS MISTAKES
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Source: Adapted from Fig. 2.6, Guidelines for Preventing Human Error in Process Safety, AIChE, New York, 1992
Factors Influencing Human Performance
As humans interface with processes and systems, they can be considered a liability or a
safeguard. Factors that influence performance and create liability need to be considered
when attempting to identify potential human error hazards. The following factors must
be considered when attempting to identify the potential for human error.
Economic and Political Environment
regulatory climate
legislation
general economic conditions
Corporate Policy and Management Systems
safety culture and policies
resource allocation
Process Environment
materials handled
complexity of process
frequency of human interaction
perceived danger by workers
protective clothing and equipment
Physical Work Environment
noise
lighting
temperature
environmental conditions
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Work Control Systems
supervision
standard, emergency, maintenance and contractor procedures
level, clarity and frequency of training/instruction
quality of checks and warnings
frequency of use
Working Conditions
work hours
shift rotations
distribution of work contractor interaction
Operator Attributes
training
skill and experience
physical/intellectual capability
morale and motivation
Human Error In Accident Causation
Human error is either an active or a latent (waiting to happen) error.
Active Human Error
Active human error has an immediate and direct effect on the cause of a hazardous
situation or is the direct initiator of a chain of events, which leads to an accident.
Latent Human Error
Latent human error is different in that the consequences of the error may only become
dynamic after a period of time when the condition caused by the original error combines
with other errors or system failures to bring about unsafe conditions.
Latent human error is of the most concern for PHA teams. Most latent human errors
occur at the engineering design or at management policy level. It is at the engineering
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design level that PHA study teams must be most vigilant. For instance, inappropriate
design for valve placement or inadequate space allowed for worker movement in
attending to routine inspections and maintenance will increase the probability of active
errors.
The Flixborough disaster discussed in the video in the introductory session is an example
of latent human error. Engineering staff should have realized that the constant pressure
fluctuations within and between the reactors would have an adverse effect on the
temporary bypass pipe if it were not adequately supported.An error of this kind would
have been picked up in a well-conducted PHA of the modification.
The value of having knowledgeable and diversely experienced PHA team members
becomes particularly evident when dealing with the potential for human error during a
PHA.
WINDOW OF INCIDENT OPPORTUNITY
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Inappropriate policies at the corporate level, or incorrect or deficient implementation of
policies by management at the line level can create an error inducing environment at the
operational level. This environment at the process and physical work level leaves the
door for actions or decisions that are unsafe. If engineering and human defenses against
foreseeable hazards at any level prove inadequate, an incident will occur.
The individual who performs the action leading to an incident is usually the last straw
that breaks the system already made vulnerable by the latent errors of poor management.
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Human Error Risk Reduction Checklist at Different Levels of Interaction
MANAGEMENT
Tangible management commitment to
facility safety and training is shown.
Process safety information is keptcomplete and current.
Safety policies are clearlycommunicated to employees.
Appropriate employee participation ispart of safety management.
PROCEDURES
A task analysis has been performed.
Critical tasks have been identified.
Critical task deviations have beenanalyzed for potential hazards.
Tasks are designed for the humans whowill perform them.
Routine/non-routine and emergencyprocedures are current, appropriate,clear, concise and consistent.
Procedures provide quality checks andwarnings.
Procedures are used.
WORKING CONDITIONS
Noise, lighting and temperature are atappropriate levels.
Adequate protective clothing andequipment is provided.
Hours worked are appropriate forcomplexity of continuous taskperformance.
Shift rotation allows for optimalperformance.
DESIGN AND CONSTRUCTION
Equipment is accessible, clearlylabeled.
Materials used comply with appropriatecodes and standards.
Adequate safety measures are built intodesign.
Adequate containment of hazardouschemicals is built into design.
Buildings are designed and sited tocomply with existing guidelines andstandards for worker and equipmentprotection.
Buildings are appropriately located inrelation to hazardous materials or
processes.
TRAINING
Quality training is provided for all newemployees.
Performance is evaluated and trainingis refreshed regularly.
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Siting Issues in Facility Risk
Siting issues should be addressed in every PHA, or for a large complex facility, siting can
be the subject of its own specialised PHA. Siting includes the physical site of the
facility, the location and layout of equipment, and the location of hazardous materials,processing and storage. Siting issues are considered in relation to the people who occupy
the site for any length of time and the geographic and environmental implications.
During a PHA, the following are some of the issues that need to be considered.
Site Selection Considerations:
(Usually considered at conceptual stage of facility lifecycle.)
adjacent facilities
nearby communities
transport availability
availability of utilities (e.g. power and water)
topography and average weather conditions
environmental sensitivity
Layout Considerations:
industry and insurance guidelines and statutory regulations
process materials being handled or stored (inherent properties)
extremity of physical process conditions
location and spacing of process plant buildings and equipment to provide access
for routine operation and emergency services
location and spacing of process plant buildings and equipment to ensure safe
distances from process and storage of hazardous chemicals
buffer zones between hazardous material storage and extreme processes to reduce
potential for domino effects
building design and construction standards to withstand the intrusion of fire,
explosion and toxic effects
occupancy level of areas in proximity to process units and material storage
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Protective Mechanisms and Equipment:
containment
drainage
fire proofing
ventilation
explosion barriers
crash barriers
fire water supply
NOTE: PHA-Pro provides a comprehensive Siting Checklist in the OSHA templates
Environmental Issues in Facility Risk
PHAs are not only interested in the safety of life and production, but international
regulations and human responsibility insist that they are also interested in the safety of
the environment.
The following are some of the issues that should be considered during a PHA.
On and off-site contamination:
ground water contamination contaminated surface water run-off
soil contamination
plant life
food chain
air quality and ozone depletion
Human impacts:
Chronic and acute exposure to toxic materials through contaminated drinking water,
agricultural products and air.
allergies
eye irritation
lung damage
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genetic mutations
poisoning
Wildlife impacts:
migratory routes
critical habitats for endangered species
genetic mutations
Domestic animal impacts:
contamination of feed and water
genetic mutations
poisoning
impact on agriculture and food supply
Micro/Macro biological impacts:
ecosystems
food chain
surface and ground water
air quality
eradication of habitat or species
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PPHHAA TTEEAAMMSS
A PHA is performed by a multidisciplinary team experienced in engineering, operations
and maintenance. Other relevant experts should be included as required. At least one
member of the team should have knowledge specific to the process being evaluated and
at least one member should be knowledgeable in the PHA methodology being used and
impartial in the evaluation.
Size of PHA Team
As few as two or three and as many as seven or eight depending on the
methodology chosen and the size and complexity of the facility. Too many
participants reduce the efficiency of any PHA.
Why a Team Approach?
Advantages of team approach:
Range of expertise and experience creates a wide information pool base for
decision-making.
Representatives from different cultural groups in a facility can bring multiple
perspectives to problems and the implications of proposed actions. (See article
Culture in Appendix.)
Multidisciplinary teams provide an inclusive safety culture in which to learn
about, and understand other operating cultures.
Groups can make higher quality decisions because they have a greater combined
capacity to comprehend a problems complexities and its alternative solutions.
Groups can fill in each others blind spots and jolt each other out of rigid
thinking.
Groups can help each other see the big picture more clearly.
Groups stimulate creativity by piggy backing on each others ideas to
sometimes create an unusual solution to a routine problem.
Groups can enhance commitment of participants to carry out the groups decision.
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Disadvantages of team approach:
Time Pressure
Groups can feel the pressure of time and rush through a discussion so it is
necessary to avoid using arbitrary deadlines; assess the demands of the task
realistically before estimating the deadline.
Social Pressure
Groups can feel pressure to conform to group norms (e.g. participants will
frequently accept the first feasible solution that seems acceptable to the majority
of members while other, perhaps superior, solutions go unexamined).
Groups can succumb to groupthink and minimise critical testing of ideas
because of a fear that conflict will create disharmony (often happens in close knit
groups such as facility co-workers).
Ego Pressures
Group pressure sometimes can lead to ego defensive strategies that are counter-
productive to group efficiency.
Domination of discussion by one individual can inhibit challenges to the ideas of
the talker and the presentation of alternative points of view.
Apprehension by participants perceiving themselves as having lower status than
others in the group can lead to acquiescence to the ideas of members seen as
having higher status.
A competitive environment destroys group effectiveness when members allow
individual goals of winning the argument to take priority over the shared goal of
solving the problem.
Egocentric communication within a group does not listen to the ideas of others so
decisions are often made according to whoever pushes their own point of view the
hardest.
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It is the responsibility of both participants in PHAs and the leaders of PHA teams to
recognize the negative potential within the group and work towards creating group
cohesion and efficiency.
Responsibility of Group Participants in PHAs
Be on time - commit to schedule and study goals.
Remain focused.
Respect the ideas of others.
Actively participate.
Critically evaluate ideas not the person who presented the idea.
Contribute all relevant information and ideas.
Be prepared for some degree of conflict.
Think in the long term as well as the here and now.
Be prepared to find out if you do not know.
Think laterally, keep an open mind. Think, out of the box.
Note: PHA leadership responsibilities will be addressed in detail in a later section.
Thinking Skills Required of Participants in PHAs
Creative Thinking Skills
Creative thinking requires that you deviate from the routine or common ways of
doing things to find unique solutions to problems.
Creative thinking listens to intuition and hunches and explores them for their
potential.
Creative thinking is able to adapt to different thinking modes and combine the
thinking outcomes
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Thinking Modes
Teams work best when a number of different personality/information processing
styles make up the group and a conscious effort is made by team members to
adopt different thinking modes.
objective thinking just the facts (interested in concrete details)
intuitive thinking (listen to your gut feeling)
worst case thinking (What is the worst thing that could happen?)
best possible scenario of what is practical and beneficial
forward thinking of alternatives, solutions and linking of old and new
Big picture thinking that organises and controls the detailed thinking
process
Critical Thinking Skills
Effective decision-making requires critical testing of assumptions, ideas and
arguments.
Critical thinking explores as many bases as possible for acceptance or rejection of
an idea by asking questions that test the relevance of assumptions and inferences
and finds holes in the logic of arguments.
E.g. It is assumed and inferred by the P&ID being studied that product will
normally flow from point A to B safely and without interruption to operation. To
test this assumption it is questioned:
Could there be no flow?
How could it occur?
What would be the consequences of no flow?
Would the consequences be hazardous or would it prevent efficient operation?
What are the solutions?
Warning:
To protect the egos of those who offer ideas, the group should consider an idea a
separate entity that belongs to no one once it enters the group discussion.
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Exercise:
To test your creative and out of the box critical thinking skills, mount the jockey on the
horse.
After completing exercise, think how the kind of thinking you applied to the task could
also be adapted to identifying hazards and finding solutions to hazardous situations.
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PPHHAA MMEETTHHOODDOOLLOOGGIIEESS
Video Process Hazards Analysis
In this video, you will see an overview of PHA and the most often used techniques. Use
the remainder of the space to make any notes.
NOTES:
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General PHA Procedure Flow Chart
Define Node or System
Hazard Identification - Various Methodologies
Accident Likelihood
Estimation
Accident Severity
Estimation
Risk Ranking
Recommendation
Accept risk Modify system
Operate System
Possible Hazard Consequences
Identify Existing Safeguards
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Objectives of a Good PHA Study
To identify hazards, not to necessarily provide solutions to hazards.
To provide the greatest possible confidence that all of the potential hazards are
identified while taking up the minimum resources needed to get the job done.
To provide a qualitative estimate of the likelihood and the severity of potential
accidents.
To qualitatively evaluate the consequences of failed engineering and
administrative controls.
To provide management with a concrete and easy to use basis for making risk
management decisions.
To identify ways in which operability might be improved.
To provide information which can be useful in improving future designs.
To provide objective documented evidence of a thorough well conducted study
for audit and insurance purposes.
PHAs are only as effective as the action taken to implement the recommendations
made during the study.
Process Safety Information for Hazards Analysis
The quality of any PHA depends directly on the quality and quantity of information
available to the study team. Differing amounts of information will be available at
different facility lifecycle stages and will, therefore, affect the PHA methodology chosen.
For a satisfactory PHA, easily accessible information is required, at the least, about the
hazards and characteristics of the chemicals used, about the process technology and how
it works, and about the equipment used in the process.
Video Process Safety Information
In this video, you will learn about some of process information required for a PHA and
how to gather it in a time effective manner. Use the remainder of the space to make any
notes.
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NOTES:
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The video pointed out the need for hazardous material information and for information
about the technology of the process under review. The following gives a comprehensive
list of necessary and ideal process safety information for a PHA.
As a minimum the following information should be available for any PHA:
Material Safety Data Sheets (MSDS) for all hazardous, toxic or explosive
chemicals
process flowsheets and material balance information with a range of operating
pressures
temperatures, flows, levels and compositions
safe upper and lower limits for pressures, temperatures and flows
overview of the process and a process description
Mechanical Flow Diagrams (MFD)
shutdown key or emergency shutdown system logic diagrams
operating and maintenance procedures
list of safety critical components
Emergency Response Plans (ERPs)
If possible also try to access the following information:
plot plans and equipment layouts Piping and Instrument Diagrams (P&IDs)
electrical single line diagrams and area classification drawings
flare, vent and relief system design basis
relief valve specification sheets and design capacities
building ventilation design basis
flare and gas detection design basis
equipment failure history logs and failure analysis
fire system design basis, i.e., extinguishers, firewater, dikes, protective coatings
and firewalls
process equipment specification sheets or fabrication drawings and applicable
piping, electrical or foundation design specifications
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Methodologies Overview
HAZard and OPerability Analysis (HAZOP)
HAZOP is the most comprehensive PHA at all stages of facility life, from detailed design
through construction and routine operation. It identifies operability problems as well as
hazards to personnel, the public, company property and the environment.In a HAZOP study, the process under review is first broken down into nodes, which are
logical and manageable segments that have a definable design intent. Each node is
studied in detail by applying each of the relevant guidewords to design parameters to
identify potential cause and consequence of hazards and operability problems. Equipment
failure, human error, engineering and administrative controls, and external events are all
considered as potential causes of hazards. Using a Risk Ranking Matrix, severity and
likelihood rankings are estimated and a numerical risk ranking is assigned to each
identified hazard.
Requires considerable amounts of process and safety information.
Uses systematic, structured examination augmented by creative team thinking.
Encourages interaction of team members with diverse backgrounds and
knowledge.
Looks at equipment, instrumentation, utilities, human action (routine and non-
routine), building and equipment siting, procedures, and external factors to reveal
hazardous situations.
Ranks identified risks for severity and likelihood (for sample Risk Ranking
Matrix see page 91).
Can be made applicable to almost any industry, process or system.
Can be used effectively to perform job task analyses and procedures.
Makes note of existing safeguards and evaluates them for sufficiency.
Ensures each recommendation is thoroughly explored because of the diverse team
member agendas.
Can be limited by the assumption the process will be operated as it was designed
to operate.
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People Requirements:
leader experienced in the technique.
up to eight (maximum) team members with specific knowledge about some aspect
of the process being reviewed (too many can slow study and reduce quality).
example team members:
chemical, electrical, mechanical engineering specialists
safety specialist
environmental specialist
toxicologist
vendor representative
maintenance personnel and operators
Objectives of HAZOP Analysis:
to determine if process deviation can lead to undesirable consequences.
to identify operability problems as well as hazards to personnel, the public,
company property and the environment.
to identify where more research into cause and consequence need to be
conducted.
to recommend changes or improvements to design or operation.
Approximate Time Required for HAZOP:
Depending on the size and complexity of process or modification preparation
can take from 1 - 4 days (leader) analysis, from 1 day to several weeks
documentation, 2 days.
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Select Drawings for Review
Explain Process Involved
Select Node for Review
Explain Intent of Node
Select a Parameter
Apply Guidewords/Develop Deviations
Identify Causes
Assign Cause Categories (if desired)
Identify Possible Consequences
Estimate Severity and Likelihood (Risk Ranking)
Identify Existing Safeguards
Make Initial Recommendations
Are Other Guidewords Applicable?
Are Other Parameters Applicable?
Drawing Complete
No
No
Yes
Yes
STEPSINHAZOPANALYSIS
Any Other Nodes?
Yes
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Sample Guideword Meanings
GUIDEWORDS
NO/NONE
MEANINGS
The negation of design intentions/Intention is not achieved
MORE/HIGHERQuantitative increase (above design intent) or morecomponents in the system than design intent
Usually in reference to measurable physical properties suchas flow, and temperature or extra phase, impurities, etc.
LESS/LOWQuantitative decrease (below design intent) or fewercomponents in the system than design intent
Usually in reference to measurable physical properties suchas flow and temperature
AS WELL ASQualitative increase
Something in addition to design intent is achieved
PART OF
Composition of system different from what it should be
Only part of design intent is achieved - something ismissing
REVERSE/MISDIRECTEDLogical opposite of design intent
Usually in reference to actions such as flow or chemicalreaction
OTHER THAN including
SOONER/LATER
Alternative mode (What else can happen)
Substitution of something other than design intention
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Sample Guidewords and Parameters for Creating Deviations from Design Intent for
HAZOP Studies
DEVIATION. GUIDEWORD. PARAMETER
As well as.......................................................As well asLess ................................................................LessMore...............................................................MoreNo...................................................................NoOther than.......................................................Other thanReverse...........................................................ReverseSooner/Later...................................................Sooner/LaterHigh Agitation/Recirculation.........................High........................................AgitationLow Agitation/Recirculation .........................Low ........................................Agitation
No/Less Component Separation ....................Less.Component Separation
Contaminants Enter Compressor ...................As well as...............................CompositionContaminants .................................................As well as...............................CompositionContamination................................................As well as...............................CompositionHigh Concentration of Impurities ..................As well as...............................CompositionHigh Contaminants ........................................As well as...............................Composition
No/Less Cooling ............................................Less ........................................CoolMore/Excess Cooling.....................................More.......................................Cool
Casing Rupture...............................................Other than...............................FlowHigh Flow ......................................................High........................................Flow
Leak................................................................As well as...............................FlowLeakage..........................................................As well as...............................FlowLow Flow.......................................................Low ........................................FlowLow/No Flow.................................................Low/No ..................................FlowMore/High Flow.............................................More.......................................FlowNo/Low Flow.................................................Low/No ..................................FlowReactor Rupture .............................................Other than...............................FlowReverse/Misdirected Flow .............................Reverse/Misdirected ..............FlowRupture...........................................................Other than...............................FlowShell Leak ......................................................As well as...............................FlowShell Rupture .................................................Other than...............................FlowTube Rupture .................................................Other than...............................FlowTube Leak ......................................................As well as...............................Flow
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More/Excess Heating.....................................More.......................................HeatMore Fire/Explosion Risk..............................More.......................................HeatNo/Less Heating.............................................Less ........................................Heat
Loss of Instrumentation/Control....................No.Instrumentation/ControlHigh Interface Level ......................................High.Interface LevelHigh/Excess Interface Level..........................High.Interface LevelLow Interface Level .......................................Low ........................................InterfaceLow/Reduced Interface Level........................Low ........................................Interface
High/Excess Level .........................................High........................................LevelHigh Bottoms Level.......................................High........................................LevelHigh Level .....................................................High........................................LevelLess/Reduced Level .......................................Less ........................................LevelLow Bottoms Level........................................Low ........................................Level
Low Level ......................................................Low ........................................LevelLow Tray Level..............................................Low ........................................Level
More Load on Structures ...............................MoreLoad on StructuresMore Load on Flare System...........................More.......................................Load to Flare
Maintenance Hazards.....................................Other than...............................Maintenance
Cavitation.......................................................As well as...............................PerformanceColumn Flooding ...........................................Part of.....................................PerformanceLoss of Performance ......................................Other than...............................Performance
High Pressure.................................................High........................................PressureHigh Discharge Pressure................................High........................................PressureHigh Suction Pressure....................................High........................................PressureLess/Low Pressure .........................................Low ........................................PressureLow Suction Pressure ....................................Low ........................................PressureLow Pressure..................................................Low ........................................PressureLow Pressure..................................................Low ........................................PressureMore/High Pressure .......................................More .......................................Pressure
High Reaction Rate........................................More.......................................ReactionLow Reaction Rate.........................................Less ........................................Reaction
Start-up/Shutdown Hazards ...........................Other than...Start-up/ShutdownHigh Temperature ..........................................High........................................TemperatureHigh Discharge Temperature.........................High........................................Temperature
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Less/Low Temperature ..................................Low ........................................TemperatureLow Temperature...........................................Low ........................................TemperatureMore/High Temperature ................................High........................................Temperature
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Preliminary Hazards Analysis
Preliminary Hazards Analysis identifies potential hazards at the conceptual stage of a
design when they can be corrected with minimal cost and disruption.
General focus is on the hazardous materials to be handled, the layout, operating
environment, and major process areas of the facility.
Hazards can be identified while it is still possible to make cost effective changes.
For each definable area of the process, potential hazards are identified, possible
causes and worst case consequences are listed and suggestions are made to correct
the problem.
Not considered a comprehensive study because little information on design details
or procedures is available.
Usually followed later by a more comprehensive analysis.
People Requirements:
Can be performed by as few as two people with process safety backgrounds.
Because analysts are required to use their own judgment, experienced leaders and
participants are preferable to ensure an exhaustive and detailed analysis.
Objectives of Preliminary Hazards Analysis:
to provide information required to make fundamental decisions about facility
siting, unit operations and special design considerations.
to identify areas where more research is required to ensure a safe, effective
process and design.
to provide an opportunity to incorporate recommendations into design.
to prioritise hazards in existing facilities when more extensive techniques are not
available.
Approximate Time Required for Preliminary Hazards Analysis:
Depending on the size and complexity of process, preparation can take from .5 -
3 days (leader only) analysis, from 1 - 6 days documentation, from 1 - 4 days.
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Recommended Process Safety Information:
plant design criteria
plant equipment specifications
material specifications
proposed facility layout if available
Steps in Preliminary Hazards Analysis:
1. Leader reviews all available material prior to first meeting to develop list of
possible hazards and checklist questions about location, environment and weather,
process materials, emergency equipment, etc.
2. Meeting: Leader suggests a potential hazard (e.g. toxic release) and follows the
process from beginning of flow to end, prompting with questions and encouraging
the team to question and think creatively about all possibilities.
3. Causes for the hazard are identified and documented.
4. Consequences are estimated and documented.
5. Severity and likelihood factors are estimated and risk ranking assigned.
6. Suggestions are made for improvements and documented.
7. Leader suggests next hazard and the process repeats itself.
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Checklist Analysis
A detailed list of questions, written from knowledge and experience is used to assess the
acceptability or status of the process, system or operation compared to standard design
and operating practices.
Checklist Analysis is an experience-based methodology and its value is dependent
on the quality of the checklist.
Operating systems are defined and lists of questions are generated about standard
design and operating practices for each system.
Checklist questions need to be developed by a multidisciplinary team with
experience in the process being studied.
Checklists are best tailored specifically for an individual company or plant and
built upon over time.
Questions usually require Yes, No or Requires more information answers.
Can be used at any time in the facility lifecycle to evaluate materials, equipment
and procedures, but is especially effective combined with a pre-start-up safety
review if a previous hazards analysis has been conducted at the detailed design
stage.
Can be as detailed as required for the purpose.
Can be combined with What-If Analysis for comprehensive evaluation of hazards. Can be used as an investigative tool to identify hazards and an audit tool to verify
designs and installations.
Is not an aid to identification of unknown hazards.
Does not identify operability problems well.
People Requirements:
Requires a leader who is knowledgeable in the process and experienced in start-up
and construction.
Requires people experienced in the system/process as it is being studied.
Does not require same team members at all times. Experts come and go as
required.
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Objectives of Checklist Analysis:
to verify compliance with design, codes and regulations at startup.
to help control management of change.
to aid in a comparative review of process not yet built.
to act as an aid in training people inexperienced in a process.
Approximate Time Required for Checklist Analysis:
Depending on the size and complexity of process, preparation can take from .5 -
3 days (experienced engineers and maintenance/operations personnel to generate
checklist questions) analysis, from .5 - 5 days documentation, from .5 - 4 days.
Checklists
Checklists generated from experience, standards and codes and industry
guidelines and any other authoritative references such as engineering and
construction drawings, equipment specifications and previous hazards analysis
study findings.
Checklists can be developed by a number of people with experience in specific
parts of the process or plant. (Sample Checklist can be found in Appendix.)
Steps in Checklist Analysis:1. Acquire or develop appropriate checklists.
2. Expert team members tour the subject process with leader and compare
equipment and operation to checklist items.
3. Deficiencies are noted.
The Checklist process can be performed on a not yet built facility in a meeting room with
the team members reviewing the process drawings, completing the Checklist and
documenting their discussion of the deficiencies.
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What-If Analysis
What-If Analysis uses a creative team brainstorming what if questioning approach to
the examination of a process or operation to identify potential hazards and their
consequences. Users should be experienced and creative thinkers.
Questions that begin with what-if are formulated by engineering personnel experienced
in the process or operation and subdivided into specific categories of interest.
For example:
What if the raw material being introduced is the wrong concentration?
What if the operator forgot to manually close the valve?
Questions can also focus on specific consequences such as process safety,
operating procedures, human error or environmental safety. Does not easily
generate operability information.
Questions are applied to existing P&IDs and process descriptions.
Questions are usually added as the analysis progresses.
Hazards are identified, existing safeguards noted and qualitative severity and
likelihood ratings are assigned to aid in risk management decision-making.
Loose structure necessitates experienced team. Can only provide high level of assurance with very knowledgeable, experienced
and creative team.
Often used at design concept stage and to analyse proposed changes to a facility.
People Requirements:
Leader experienced in the What-If Technique and five or six participants
knowledgeable and experienced in the subject process.
Objectives:
to aid in identification of possible deviations from design, construction,
modification or operating intent.
to identify hazards and suggest risk reduction methods.
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Approximate Time Required for What-If Analysis:
Depending on the stage of project development and the size and complexity of
process or modification, preparation can take from .5 - 3 days (leader) analysis,
from .5 - 6 days documentation, from .5 - 3 days
Steps in a What-If Analysis:
1. Provide relevant information to selected team members in sufficient time before
the study for their input in developing What if questions.
2. Leader divides process into logical systems and subsystems.
3. Scope and objectives of study are explained.
4. Existing safety precautions and equipment are described.
5. Team reviews information to generate more questions related to the systems of
the process.
6. List of questions is made.
7. Systems and subsystems are analysed from the beginning of the process to the end
by applying the relevant what if questions.
8. Potential hazards are identified and consequences estimated and documented.
9. Severity and likelihood factors are given and a risk ranking assigned and
documented.
10. Recommendations for improvement are made and documented.
In some cases, responsibility for follow-up on the recommendations is assigned to
individual parties or departments and documented.
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What-If/Checklist Analysis
What-if/Checklist Analysis combines the creative brainstorming features of the What-If
Analysis with the systematic features of the Checklist Analysis to provide a
comprehensive method of identifying hazards.
Creative questioning augments the systematic experienced based checklist to
provide a more complete study.
Checklists are generally structured to focus on general sources of hazards and
accidents.
Study can begin with a checklist to which what-if questions are applied to
round out gaps in the list.
Alternatively, study can begin with a brainstormed identification of hazards
followed by the structure of a checklist.
Can be used successfully at any stage in facility lifecycle.
Requires a team experienced in the process under review.
Usually provides a less detailed review than the more structured analyses such as
HAZOP.
Can be structured to provide detailed analysis but this can be time consuming
unless checklists and questions can be used from previous studies.
Objectives of What-If/Checklist Analysis:
to identify and evaluate the most common hazards in a process.
to provide a qualitative evaluation of the consequences of accident outcomes.
to evaluate the adequacy of existing safeguards.
Approximate Time Required for What-If/Checklist Analysis:
Depending on the stage of project development and the size and complexity of
process or modification, preparation can take from .5 - 3 days (leader) analysis,from .5 - 6 days documentation, from .5 - 3 days.
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Failure Modes and Effects Analysis (FMEA)
FMEA is not strictly speaking a hazard identification technique, but it provides an
important source of hazard information because it documents and describes all the ways
in which individual pieces of equipment can fail and the effects of such failure on a
facility.
Can be used at all stages of a facilitys life and can be easily updated for plant
modifications.
Requires knowledge of equipment function and failure modes as well as facility
function and its potential response to equipment failure.
Requires consistent format and procedure to help ensure efficient study.
Can be conducted at component or system level.
Each equipment item within a defined system is evaluated for its failure modes.
Identifies and describes all possible ways in which equipment fails (failure
modes) e.g. On/off, open/closed, etc.
Identifies only single failure modes that cause or contribute to an accident (e.g.
individual failure is considered an independent occurrence).
Not effective in identifying the combinations of equipment failures that result in
an accident.
Investigates and documents each failure modes effect on facility safety. System level hazards can be analysed by focusing on the individual pieces of
equipment that make up the system while keeping in mind the overall effect on
the subject system.
People Requirements:
requires leader experienced in the technique.
can be conducted with as few as two or three team members with knowledge of
equipment function and potential failure modes as well as facility function and its
potential response to equipment failure.
Objectives of FMEA:
to provide a list of equipment and their potential failure modes.
to describe how equipment fails.
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to evaluate the effects of equipment failure on other parts of the process or system
in a facility.
to make recommendations for improving equipment reliability.
Approximate Time Required for FMEA:
Depending on the number of equipment items and the complexity of process or
modification, preparation can take from .5 - 3 days (leader), analysis, from 1
day - several weeks documentation, from 2 - 8 days
Steps in an FMEA:
1. Establish the physical and operating boundaries of the study.
2. Identify and describe each equipment component.
3. Beginning at the beginning of a system boundary, evaluate the equipment items in
the order that they appear on the process flow diagram.
4. List and evaluate all failure modes for each component before proceeding to the
next.
5. For each failure mode, describe the immediate and surrounding effects and the
anticipated effects on other equipment and overall system using a worst-case
scenario assuming safeguards do not work. Document findings.
6. Estimate a qualitative rating of likelihood and severity, and by combining these
ratings, provide a qualitative risk ranking. Document findings.
7. Describe the existing safeguards or procedures that can mitigate the consequences
of equipment failure. Document findings.
8. List recommendations for corrective actions for further evaluation. Document
findings.
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Other PHA Methodologies Reserved for Specific Safety Concerns
The following PHAs are hazard evaluation techniques rather than hazard identification
techniques and are generally quantitative in nature, time consuming and require special
expertise and statistical data.
Fault and Event Tree Analyses and Cause/Consequence Analysis
Both provide graphical representations of accident root causes and sets of failures that
could result in an accident.
Quantitative Risk Analysis (QRA) (Hazan) (Risk Assessment)
See page 5.
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Advantages and Disadvantages of PHA Methodologies
ADVANTAGES DISADVANTAGES
PRELIMINARY
HAZARDSANALYSIS
Identifies the potential for majorhazards at a very early stage of projectdevelopment.
Provides basis for design and sitingdecisions.
Helps to ensure plant to plant and plantto environment compatibility.
Facilitates a later full hazard analysis.
Is not comprehensive and must befollowed by a full HAZOP beforeconstruction begins.
CHECKLIST Easy to use, relatively quick.
Quick way to verify compliance withcodes and regulations.
Limited by authors experience andknowledge.
Does not identify new or unknownhazards.
Does not directly address operabilityproblems.
WHAT-IF Team of relevant experts extendknowledge and creativity pool.
Easy to use.
Ability to focus on specific element(e.g. human error or environmentalissues).
Quality dependent on knowledge,thoroughness and experience of team.
Loose structure can let hazards slipthrough.
Does not directly address operabilityproblems.
WHAT-IF/
CHECKLIST
Combines creative brainstorming withstructured checklist.
Flexible level of detail.
Quality dependent on knowledge,thoroughness and experience of team.
Does not directly address operabilityproblems.
FMEA Systematic, component by componentanalysis aids thoroughness.
Beneficial at all stages of a facilityslife.
Can easily be updated for plantmodifications.
Not efficient for identifyingcombinations of equipment failure.
Does not directly address siting issues,general safety and environmentalissues.
Does not directly address operabilityproblems.
Can be time consuming.
HAZOP Most systematic and comprehensive ofmethodologies.
Can be used in conjunction with HumanError analysis.
Only PHA to address both safety andenvironmental hazards and operabilityproblems.
Provides greatest safety assurance.
Can be time consuming and costly.
Can be tedious if not well facilitated.
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Limitations of PHA
Like any analysis, PHAs are subject to limitations. Users must understand and respect
these limitations when participating in or leading PHAs or when using the results of a
study to reduce risk. Can never guarantee that all hazards, causes and consequences have been
identified.
Are only effective if it can safely be assumed that the facility is operated in the
manner intended by the designers and in accordance with good practice.
Are only relevant to the time conducted. Even minor changes may significantly
impact facility safety.
Are subjective and only as good as the collective knowledge, creativity and
experience of the team.
Can only be effective and comprehensive if the information available is complete,
accurate and up to date.
May overlook hazards related to material quality and workmanship.
Are only effective if action is taken to implement the recommendations made
during the study.
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MMEETTHHOODDOOLLOOGGYY SSEELLEECCTTIIOONN CCRRIITTEERRIIAA
The range of PHA methodologies affords flexibility of study objective. There is not
always any one best methodology for a specific process or operation. Regardless of
methodology, the effectiveness of any study is greatly enhanced if the team is
knowledgeable and experienced and is lead by a person also knowledgeable and
experienced in the technique being used.
The following criteria for methodology selection will provide a basis for making initial
decisions, but only experience will provide the knowledge and confidence to make the
right choice for the defined purpose.
NOTE:
A danger exists that a less appropriate methodology may be chosen to save time or
because of inadequate financial or people resources. Under funded, understaffed or
rushed studies are not destined for success.
Factors to Consider When Selecting THE Appropriate PHA Methodology
Purpose of StudyThe purpose of the study is the most important factor in selecting an appropriate
methodology. The reason for the study must be clearly defined by management.
For Example:
Is the study part of policy for all new facilities?
Are the study results to be used for risk reduction planning in an existing facility?
Is the study required for regulatory compliance or insurance purposes?
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Type of Results Required
Knowing how the results will be utilised or could be utilised will help determine which
methodology to use.
For Example: simple list of identified hazards or accident scenarios for emergency planning
purposes
prioritized estimations of likelihood and severity for future quantitative risk
analysis purposes
recommendations to reduce hazards and minimize operability problems for risk
reduction planning
legal and regulatory compliance
Type of Information Available
Information needs to be of good quality and current. Using unsuitable or out of date
information is a waste of time and can, in fact add to the hazardous situation at a facility
by providing a false sense of security or incorrect risk management information.
More information becomes available in the evolution of a facility, from concept to
normal operation. Therefore, studies performed at the early stages of a design, of
necessity, must be more simp