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Major Hazard Facilities Major Accident Identification and Risk Assessment. Overview. This seminar has been developed in the context of the MHF regulations to provide: An overview of MA identification and risk assessment The steps required for MA recording

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Major Hazard Facilities Major Accident Identification and Risk Assessment

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Presentation Transcript
  • This seminar has been developed in the context of the MHF regulations to provide:
    • An overview of MA identification and risk assessment
    • The steps required for MA recording
    • Examples of major accidents identified
    • The steps required for a risk assessment
    • Examples of risk assessment formats
some abbreviations and terms
Some Abbreviations and Terms
  • AFAP - As far as (reasonably) practicable
  • BLEVE – Boiling liquid expanding vapour explosion
  • BPCS – Basic process control system
  • DG - Dangerous goods
  • Employer - Employer who has management control of the facility
  • Facility - any building or structure which is classified as an MHF under the regulations
  • HAZID - Hazard identification
  • HSR - Health and safety representative
  • LOC - Loss of containment
  • LOPA – Layers of protection analysis
  • MHF - Major hazard facility
  • MA - Major accident
  • SIS – Safety instrumented system
topics covered in this presentation
Topics Covered In This Presentation
  • Regulations
  • Definition - Major accident (MA)
  • MA identification issues
  • Approaches to MA identification
  • MA recording
  • Pitfalls
topics covered in this presentation5
Topics Covered In This Presentation
  • Definition of a risk assessment
  • Approaches
  • Risk assessment
  • Likelihood assessment
  • Consequences
  • Risk evaluation and assessment
  • Summary
  • Sources of additional information
  • Review and revision

Occupational Health and Safety (Safety Standards) Regulations 1994

  • Hazard identification (R9.43)
  • Risk assessment (R9.44)
  • Risk control (i.e. control measures) (R9.45, S9A 210)
  • Safety Management System (R9.46)
  • Safety report (R9.47, S9A 212, 213)
  • Emergency plan (R9.53)
  • Consultation

Occupational Health and Safety (Safety Standards) Regulations 1994

  • All reasonably foreseeable hazards at the MHF that may cause a major accident; and
  • The kinds of major accidents that may occur at the MHF, the likelihood of a major accident occurring and the likely consequences of a major accident.

Regulation 9.43 (Hazard identification) states:

The employer must identify, in consultation with employees,

contractors (as far as is practicable) and HSRs:


Occupational Health and Safety (Safety Standards) Regulations 1994

Regulation 9.44 (Risk assessment) states:

If a hazard or kind of major accident at the MHF is identified under regulation 9.43, the employer must ensure that any risks associated with the hazard or major accident are assessed, in consultation with employees, contractors (as far as is practicable) and HSRs.

The employer must ensure that the risk assessment is reviewed:

  • Within 5 years after the assessment is carried out, and afterwards at intervals of not more than 5 years; and
  • Before a modification is made to the MHF that may significantly change a risk identified under regulation 9.43; and
  • When developments in technical knowledge or the assessment of hazards and risks may affect the method at the MHF for assessing hazards and risks; and
  • If a major accident occurs at the MHF.

Occupational Health and Safety (Safety Standards) Regulations 1994

Regulation 9.45 (Risk control) states:

The employer must, in consultation with employees, contractors (as far as is practicable) and HSRs, ensure that any risk associated with a hazard at the MHF is:

  • eliminated; or
  • If it is not practicable to eliminate the risk – reduced as far as practicable.

The employer must:

  • Implement measures at the MHF to minimise the likelihood of a major accident occurring; and
  • Implement measures to limit the consequences of a major accident if it occurs; and
  • Protect relevant persons, an at-risk community, and the built and natural environment surrounding the MHF, by establishing an emergency plan and procedures in accordance with regulation 9.53.

Major Accident

A major accident is defined in the Regulations as:

A sudden occurrence at the facility causing serious danger or harm to:

  • A relevant person or
  • An at-risk community or
  • Property or
  • The environment

whether the danger or harm occurs immediately or at a later time

ma identification issues
MA Identification Issues
  • Unless ALL possible MAs are identified then causal and contributory hazards may be overlooked and risks will not be accurately assessed
  • Likewise, controls cannot be identified and assessed
  • Identification of MAs must assume control measures are absent/unavailable/not functional

That is:


ma identification issues12
MA Identification Issues

MAs can be identified in three different areas

These are:

  • Process MAs
  • MAs arising from concurrent activities
  • Non-process MAs
ma identification issues13
MA Identification Issues

Process MAs

  • These are MAs caused by hazards which are associated with upsets in the process, or failure of equipment in the process, etc

MAs arising from concurrent activities

  • Typical concurrent operations which must be considered are:
    • Major shutdowns/start ups
    • Other activity on site
    • Activities adjacent to the facility
ma identification issues14
MA Identification Issues

Non-Process MAs

  • MAs created by non-process hazards that could cause release of Schedule 9 materials
  • Non-process hazards may typically include the following: aircraft crashing; dropped objects; extreme environmental conditions (earthquake, cyclone, high winds, lightning); non-process fires (e.g. bush fire); vehicles and road transport; heat stress
ma identification issues15
MA Identification Issues
  • Collate appropriate
    • Facility information
    • Incident data/histories
  • To ensure a thorough understanding of :
    • The nature of the facility
    • Its environment
    • Its materials
    • Its processes
ma identification issues16
MA Identification Issues
  • Develop/select a structured method for determining what types of MA can occur:
    • Loss of containment
    • Fire
    • Explosion
    • Release of stored energy
    • Where they can occur
    • Under what circumstances
  • Define and document any restrictions applied to the above
ma identification tools usage
MA Identification – Tools Usage

Examples of tools which might be used include:

  • Analysis of Schedule 9 materials and DG properties
  • Use of HAZID techniques
  • Review of existing hazard identification or risk assessment studies
  • Analysis of incident history – local, industry, company and applicable global experience
approach to ma identification
Approach to MA Identification
  • It may be efficient to treat similar equipment items handling the same Schedule 9 materials together - as often they have similar hazards and controls
  • Further, to ensure correct mitigation analysis, the equipment grouped together should contain similar materials at similar process conditions, resulting in similar consequences on release
approach to ma identification19
Approach to MA Identification
  • For consistency of analysis, all MAs should be defined in terms of an initial energy release event
  • This can be characterised as a loss of control of the Schedule 9 material
  • As an example, in the case of a hydrocarbon release from one vessel leading to a jet fire that subsequently causes a BLEVE in a second vessel, the MA should be defined in terms of the initial hydrocarbon release from the first vessel
approach to ma identification20
Approach to MA Identification
  • Review HAZID studies to identify initiating events for each MA
  • Review to ensure all hazards have been identified
  • Special checklists should be developed to assist with this process
  • Further hazards may be identified from:
    • Discussions with appropriate subject experts
    • Review of incident data
    • Review of the records from a similar system
ma recording
MA Recording
  • A structured approach is important
  • It can then link equipment management strategies and systems
  • Record the key outputs in a register

For each MA, the register should record the following information:

  • Equipment that comprises the MA
  • Group similar items into one MA
  • Description
  • Consequences
ma recording22
MA Recording
  • Consider all Schedule 9 materials - regardless of quantity
  • Screen out incidents that do not pose a serious danger or harm to personnel, the community, the environment or property
  • Screening should only be on the basis of consequence not likelihood
    • i.e. Events should not be screened out on the basis of likelihood or control measures being active
    • Consequence modelling should be used as justification for screening decisions
  • External influences need to be considered, for example, potential for a power failure to cause a plant upset leading to an MA
example ma recording
Example – MA Recording

The following are examples of MA recording details

what is risk
What is Risk?
  • Regulatory definition (per Part 20 of the Occupational Health and Safety (Safety Standards) Regulations 1994) :

“Risk means the probability and consequences of occurrence of injury or illness”

  • AS/NZS 4360 (Risk Management Standard)

“the chance of something happening that will have an impact on objectives”

  • Risk combines the consequence and the likelihood
risk assessment definition
Risk Assessment Definition
  • Any analysis or investigation that contributes to understanding of any or all aspects of the risk of major accidents, including their:
    • Causes
    • Likelihood
    • Consequences
    • Means of control
    • Risk evaluation
the risk assessment should
The Risk Assessment Should…
  • Ensure a comprehensive and detailed understanding of all aspects for all major accidents and their causes
  • Be a component of the demonstration of adequacy required in the safety report - e.g. by evaluating the effects of a range of control measures and provide a basis for selection/rejection of measures
  • The MHF Regulations respond to this by requiring comprehensive and systematic identification and assessment of hazards
  • HAZID and Risk Assessment must have participation by employees, as they have important knowledge to contribute together with important learnings
  • These employees MAY BE the HSRs, but DO NOT HAVE TO BE
  • However, the HSRs should be consulted in selection of appropriate participants in the process



Qualitative Assessment

Detailed Studies

Quantitative Risk Assessment

Asset Integrity Studies

Likelihood Analysis

Consequence Analysis

Human Factors Studies

Plant Condition Analysis

Technology Studies


Types of Risk Assessment

  • From the HAZID and MA evaluation process, pick an MA for evaluation
  • From the hazard register, retrieve all the hazards that can lead to the MA being realised
  • In a structured approach, list all of the controls currently in place to prevent each of the hazards that lead to the MA being realised
  • Examine critically all of the controls currently in place designed to prevent the hazard being realised
  • As an example, from hazard register, MA - A26

Ignition of materials

(MA - A26)


Hazard Scenario 1

Ignition of materials

(MA - A26)

Hazard Scenario 2

Hazard Scenario 3, etc


List all possible causes of the accident (identified during HAZID study)


Hazard Scenario 1







Ignition of materials

(MA - A26)

Hazard Scenario 2







Hazard Scenario 3, etc


List all prevention controls for the accident (identified during HAZID study)

likelihood assessment
Likelihood Assessment
  • Likelihood analysis can involve a range of approaches, depending on the organisation’s knowledge, data recording systems and culture
  • This knowledge can range from:
    • In-house data - existing data recording systems and operational experience
    • Reviewing external information from failure rate data sources
  • Both are valid, however, the use of in-house data can provide added value as it is reflective of the management approaches and systems in place
likelihood assessment36
Likelihood Assessment
  • A “Likelihood” is an expression of the chance of something happening in the future - e.g. Catastrophic vessel failure, one chance in a million per year (1 x 10-6/year)
  • “Frequency” is similar to likelihood, but refers to historical data on actual occurrences
likelihood assessment37
Likelihood Assessment

Likelihood Analysis can use:

  • Historical
    • Site historical data
    • Generic failure rate data
  • Assessment
    • Workshops (operators and maintenance personnel)
    • Fault trees
    • Event trees
    • Assessment of human error
likelihood assessment qualitative approach
Likelihood Assessment – Qualitative Approach
  • A qualitative approach can be used for assessment of likelihood
  • This is based upon agreed scales for interpretation purposes and for ease of consistency
    • For example, reducing orders of magnitude of occurrence
  • It also avoids the sometimes more complicated issue of using frequency numbers, which can be difficult on occasions for people to interpret
likelihood assessment fault trees
Likelihood Assessment – Fault Trees
  • A fault tree is a graphical representation of the logical relationship between a particular system, accident or other undesired event, typically called the top event, and the primary cause events
  • In a fault tree analysis the state of the system is to find and evaluate the mechanisms influencing a particular failure scenario
likelihood assessment fault trees41
Likelihood Assessment – Fault Trees
  • A fault tree is constructed by defining a top event and then defining the cause events and the logical relations between these cause events
  • This is based on:
    • Equipment failure rates
    • Design and operational error rates
    • Human errors
    • Analysis of design safety systems and their intended function
likelihood assessment fault trees example

Process vessel over pressured


Pressure rises

PSV does not relieve



Process pressure rises

Control fails high

Set point too high

Fouling inlet or outlet

PSV too small

PSV stuck closed

Likelihood Assessment – Fault Trees Example
likelihood assessment generic failure rate data
Likelihood Assessment – Generic Failure Rate Data
  • This information can be obtained from:
    • American Institute of Chemical Engineers Process Equipment Reliability Data
    • Loss Prevention in the Process Industries
    • E&P Forum
    • UK Health and Safety Executive data
    • and other published reports

(Refer to Sources of Additional Information slides for references)

likelihood assessment human error
Likelihood Assessment – Human Error
  • Human error needs to be considered in any analysis of likelihood of failure scenarios
  • The interaction between pending failure scenarios, actions to be taken by people and the success of those actions needs to be carefully evaluated in any safety assessment evaluation
  • Some key issues of note include:
    • Identifying particular issue
    • Procedures developed for handling the issue
    • Complexity of thought processing information required
likelihood assessment event trees
Likelihood Assessment – Event Trees
  • Used to determine the likelihood of potential consequences after the hazard has been realised
  • It starts with a particular event and then defines the possible consequences which could occur
  • Each branching point on the tree represents a controlling point, incorporating the likelihood of success or failure, leading to specific scenarios
  • Such scenarios could be:
    • Fire
    • Explosion
    • Toxic gas cloud
  • Information can then used to estimate the frequency of the outcome for each scenario
likelihood assessment event trees47
Likelihood Assessment – Event Trees

Event tree example – LPG Pipeline Release

  • Most scenarios will involve at least one of the following outcomes:
    • Loss of containment
    • Reactive chemistry
    • Injury/illness
    • Facility reliability
    • Community impacts
    • Moving vehicle incidents
    • Ineffective corrective action
    • Failure to share learnings
  • Consequence evaluation estimates the potential effects of hazard scenarios
  • The consequences can be evaluated with specific consequence modelling approaches
  • These approaches include:
    • Physical events modelling (explosion, fire, toxic gas consequence modelling programs)
    • Occupied building impact assessment
consequences qualitative evaluation
Consequences - Qualitative Evaluation
  • A qualitative evaluation is based upon a descriptive representation of the likely outcome for each event
  • This requires selecting a specific category rating system that is consistent with corporate culture
consequences quantitative evaluation
Consequences – Quantitative Evaluation
  • Consequence analysis estimates the potential effects of scenarios
  • Tools include:
    • Potential consequences (event tree)
    • Physical events modelling (explosion, fire and/or gas dispersion consequence modelling programs)
    • Load resistance factor design (building design)
consequences qualitative evaluation example
Consequences - Qualitative Evaluation Example

Example: Impact ofExplosions

Note: Calculations can be undertaken to determine probability of serious injury and fatality

consequences qualitative evaluation example54
Consequences - Qualitative Evaluation Example

Example - Overpressure Contour - impact on facility buildings

Release scenario location

35 kPa

21 kPa

14 kPa

7 kPa

risk evaluation
Risk Evaluation
  • Risk evaluation can be undertaken using qualitative and/or quantitative approaches
  • Risk comprises two categories - frequency and consequence
  • Qualitative methodologies that can be used are
    • Risk matrix
    • Risk nomograms
  • Semi – quantitative techniques
    • Layers of protection analysis
    • Risk matrix
  • Quantitative - quantitative techniques
risk assessment what type
Risk Assessment - What Type?

Simple, subjective, low resolution, high uncertainty, low cost

Qualitative Assessment

Semi-Quantitative Assessment

Detailed, objective, high resolution, low uncertainty, increasing cost

Quantitative Assessment

risk assessment issues for consideration
Risk Assessment – Issues For Consideration
  • Greater assessment detail provides more quantitative information and supports decision-making
  • Strike a balance between increasing cost of assessment and reducing uncertainty in understanding
  • Pick methods that reflect the nature of the risk, and the decision options
risk assessment issues for consideration58
Risk Assessment – Issues For Consideration
  • Stop once all decision options are differentiated and the required information compiled
  • Significant differences of opinion regarding the nature of the risk or the control regime indicate that further assessment is needed
risk assessment qualitative
Risk Assessment - Qualitative
  • Qualitative risk assessment can be undertaken using the following
    • Risk nomogram
    • Risk matrix
  • Both approaches are valid and the selection will depend upon the company and its culture
risk assessment risk nomogram
Risk Assessment - Risk Nomogram
  • A nomogram is a graphical device designed to allow approximate calculation
  • Its accuracy is limited by the precision with which physical markings can be drawn, reproduced, viewed and aligned
  • Nomograms are usually designed to perform a specific calculation, with tables of values effectively built into the construction of the scales
risk assessment risk nomogram61


Might well be

Very High Risk




Expected at Sometime





Very Rare,



Yearly or Less

Many Fatalities


Quite Possible

>$100M Damage

Could Happen


High Risk




Few per year

Multiple Fatalities


>$10M Damage



Unusual but


Very Serious



Once per Month



>$1M Damage








Serious Injury


Once per Week

>$100k Damage


Risk must be







Conceivable but

>$10k Damage

Very Unlikely






Minor Injury / First Aid


Acceptable if


>$1k Damage


Reduced SFARP


Risk Assessment - Risk Nomogram

Most nomograms are used in situations where an approximate answer is appropriate and useful

risk assessment risk nomogram62
Risk Assessment - Risk Nomogram

Advantages and Disadvantages

  • Accuracy is limited
  • Designed to perform a specific calculation
  • Cannot easily denote different hazards leading to an MA
  • Typically not used by MHFs
risk assessment risk matrix
Risk Assessment - Risk Matrix
  • Hazards can be allocated a qualitative risk ranking in terms of estimated likelihood and consequence and then displayed on a risk matrix
  • Consequence information has already been discussed, hence, information from this part of the assessment can be used effectively in a risk matrix
  • Risk matrices can be constructed in a number of formats, such as 5x5, 7x7, 4x5, etc
  • Often facilities may have a risk matrix for other risk assessments (eg Task analysis, JSA)
risk assessment risk matrix64
Risk Assessment - Risk Matrix
  • Results can be easily presented
    • In tabular format for all MAs
    • Within a risk matrix
  • Such processes can illustrate major risk contributors, aid the risk assessment and demonstration of adequacy
  • Care needs to be taken to ensure categories are consistently used and there are no anomalies
  • Australian/New Zealand Standard, AS4360, Risk Management 1999, provides additional information on risk matrices
risk assessment risk matrix65












Health and Safety Values

A near miss, First Aid Injury (FAI) or one or more Medical Treatment Injuries (MTI)

One or more Lost Time Injuries (LTI)

One or more significant Lost Time Injuries (LTI)

One or more fatalities

Significant number of fatalities

Medium impact outside the facility boundary

Medium impact.

Release within facility boundary

Environmental Values

No impact

No or low impact

Major impact event

Financial Loss Exposures

Loss below $5,000

Loss $5,000 to $50,000

Loss from $50,000 to $1,000,000

Loss from $1,000,000 to $10,000,000

Loss of above $10,000,000


A Possibility of repeated events, (1 x 10-1 per year)

Significant Risk

Significant Risk

High Risk

High Risk

High Risk

Moderate Risk

Significant Risk

Significant Risk

High Risk

High Risk

B Possibility of isolated incidents, (1 x 10-2 per year)

Low Risk

Moderate Risk

Significant Risk

High Risk

High Risk

C Possibility of occurring sometimes, (1 x 10-3 per year)

D Not likely to occur,

(1 x 10-4 per year)

Low Risk

Low Risk

Moderate Risk

Significant Risk

High Risk

E Rare occurrence,

(1 x 10-5 per year)

Low Risk

Low Risk

Moderate Risk

Significant Risk

Significant Risk

Risk Assessment - Risk Matrix

Risk matrix example (AS4360)

risk assessment risk matrix66
Risk Assessment - Risk Matrix


If used well, a risk matrix will:

  • Identify event outcomes that should be prioritised or grouped for further investigation
  • Provides a good graphical portrayal of risks across a facility
  • Help to identify areas for risk reduction
  • Provide a quick and relatively inexpensive risk analysis
  • Enable more detailed analysis to be focused on high risk areas (proportionate analysis)
risk assessment risk matrix67
Risk Assessment - Risk Matrix


  • Scale is always a limitation regarding frequency reduction - it does not provide an accurate reduction ranking
  • Cumulative issues and evaluations are difficult to show in a transparent manner
  • There can be a strong tendency to try and provide a greater level of accuracy than what is capable
risk assessment semi quantitative approach
Risk Assessment - Semi-Quantitative Approach
  • One tool is a layer of protection analysis approach (LOPA)
  • It is a simplified form of risk evaluation
  • The primary purpose of LOPA is to determine if there are sufficient layers of protection against a hazard scenario
  • It needs to focus on:
    • Causes of hazards occurring
    • Controls needed to minimise the potential for hazards occurring
    • If the hazards do occur, what mitigation is needed to minimise the consequences
diagrammatic representation lopa
Diagrammatic Representation - LOPA

Risk Assessment - Semi-Quantitative Approach (LOPA)

  • Analysing the safety measures and controls that are between an uncontrolled release and the worst potential consequence
risk assessment semi quantitative approach lopa




Risk Assessment - Semi-Quantitative Approach (LOPA)

The information for assessment can be presented as a bow-tie diagram

Mitigative Controls

Preventative Controls





risk assessment semi quantitative approach lopa71
Risk Assessment - Semi-Quantitative Approach (LOPA)

Advantages and Disadvantages

  • Risk evaluation can be undertaken using a bow-tie approach
  • A procedural format needs to be developed by the company to ensure consistency of use across all evaluations
  • External review (to the safety report team) should be considered for consistency and feedback
  • Correct personnel are needed to ensure the most applicable information is applied to the evaluation approach
risk assessment quantitative
Risk Assessment - Quantitative
  • Quantitative assessments can be undertaken for specific types of facilities
  • This is a tool that requires expert knowledge on the technique and has the following aspects:
    • It is very detailed
    • High focus on objective
    • Detailed process evaluations
    • Requires a high level of information input
    • Provides a high output resolution
    • Reduces uncertainty
  • Frequency component can be questionable as generic failure rate data is generally used
  • Provides understanding on the high risk contributors from a facility being evaluated
risk assessment quantitative73
Risk Assessment - Quantitative

Typical result output from such an assessment is individual risk contours

Example shown is for land use planning

risk assessment quantitative74
Risk Assessment - Quantitative
  • Time consuming
  • Expensive
  • Expert knowledge is required
  • Not suitable for every MHF site
  • Process upsets (such as a runaway reaction) cannot be easily modelled as an initiating event using standard equipment part counts - incorporation of fault tree analysis required
  • Use of generic failure rate data has limitations and does not take into consideration a specific company’s equipment and management system strategies
  • A risk assessment provides an understanding of the major hazards and a basis for determining controls in place
  • Risk assessments can involve significant time and effort
  • Operations personnel and managers could cause, contribute to, control or be impacted by MAs
  • Hence they should be involved in the risk assessment
  • HSRs may or may not take part, but must be consulted in relation to the process of HAZID & Risk Assessment
  • They should also be involved in resolution of any issues that arise during the studies, including improvements to methods and processes
review and revision
Review and Revision
  • Employer must review (and revise) Hazard Identifications, Risk Assessments and Control Measures to ensure risks remain reduced to AFAP:
    • At the direction of the Commission
    • Prior to modification
    • After a major accident
    • When a control measure is found to be deficient
    • At least every 5 years
    • Upon licence renewal conditions
sources of additional information
Sources of Additional Information

The following are a few sources of information covering risk assessment

  • Hazard and Operability Studies (HAZOP Studies), IEC 61882, Edition 1.0, 2001-05
  • Functional Safety – Safety Instrumented Systems for the Process Industry Sector, IEC 61511, 2004-11
  • Fault Tree Analysis, IEC 61025, 1990-10
  • Hydrocarbon Leak and Ignition Data Base, E&P Forum, February 1992 N658
  • Guidelines for Process Equipment Reliability Data, Center for Chemical Process Safety of the American Institute of Chemical Engineers, 1989
sources of additional information78
Sources of Additional Information
  • Offshore Hydrocarbon Release Statistics, Offshore Technology Report – OTO 97 950, UK Health and Safety Executive, December 1997
  • Loss Prevention in the Process Industries , Lees F. P., 2nd Edition, Butterworth Heinemann
  • Layer of Protection Analysis, Simplified Process Risk Assessment, Center for Chemical Process Safety of the American Institute of Chemical Engineers, 2001
  • Nomogram, Wikipedia, the free encyclopaedia