Understanding Major Accident Hazards

Training from ESR Technology

ESR Technology has built a long track-record, over many years, in delivering its Major Hazard Risk Assessment training programme throughout the Energy Industry and to its Regulators e.g. UK Health and Safety Executive Inspectors.  From this we have developed a series of free web based introductory modules to deliver an understanding of:

  • Hazard Identification – what are the hazards, can they be eliminated?
  • Scenario Definition – how might a hazardous event develop; how do we prevent it?
  • Consequence Analysis – if the event happens, how bad will it be, who or what will it harm?
  • Frequency Determination – how often is an event likely to happen, can we tolerate it?

The modules provide a high-level overview of the content within ESR Technology’s comprehensive Major Hazard Risk Assessment training programme, accessible to delegates on a module-by-module or whole course basis via on-demand/webinar sessions, and can be tailored to accommodate any specific requirements of Companies and the delegates.  They are aimed at engineers and scientists with a practical interest in the application of risk management and major hazards assessment. 


Hazard Identification – What can go wrong?

The identification of what can go wrong is an important stage of the risk assessment process.  Accidents can only be prevented by anticipating how they can occur.  Every industry operation using power, machinery, chemicals etc is hazardous, with work-place accidents like tripping, falling, electrical shocks, etc being commonplace events.  The types of hazards that we are principally concerned with here, however, are MAJOR HAZARDS, i.e. accident events that could affect a significant proportion of the workforce and also affect members of the general public outside the plant site.

Hazard identification involves the rigorous consideration of all situations in which the potential for harm may exist, followed by a disciplined analysis of the combination or sequences of events, which could transform this potential into an accident.  Normally consideration must be given to the following aspects for hazard identification relating to major hazards:

  • Determining whether a given operation or activity has the potential to give rise to a major hazard situation.
  • Determining the range of major hazard events which the operation or activity could present. This is typically performed using either:
    • Comparative Methods: these draw mainly on knowledge gained from experience. Checklists and hazard indices are comparative methods.
    • Analytical Methods: these are structured ways for stimulating a group of people to apply foresight in conjunction with their knowledge to the tasks of identifying hazardous scenarios by raising “What If?” type questions.



Scenario Definition – How could it develop?

A conceptual framework for scenario definition can be characterised as a Hazard-Vector-Target or Source-Pathway-Receptor approach as it is more commonly characterised when discussing environmental hazards. Without all three of the elements being present, no harm occurs.

Effective scenario definition depends on knowledge and experience of the hazard and relies on systematic methods to ensure that this knowledge and experience is applied to identifying the routes by which each of these major hazard events could be realised, i.e. identify potential accident scenarios.  Such accident scenarios include combinations or sequences of events, with possible escalation from an initiating minor accident event into a major hazard event.

Typically, analytical methods are used to define scenarios. These are structured ways for stimulating a group of people to apply foresight in conjunction with their knowledge to the tasks of identifying hazardous scenarios by raising “What If?” type questions.  Examples of this type of methodology are:

  • Hazard and Operability Studies (HAZOP).
  • Failure Modes and Effects Analysis (FMEA).
  • Fault tree, event tree and Bow-Ties.


Consequence Analysis – How bad will it be?

Once a scenario has been defined, consequence analysis may be undertaken to understand the impact the hazard has upon the target / receptor. This consists of:

  • Defining ‘inventories’ of hazardous materials. The ‘inventory’ may be a material with a hazardous property such as flammability or toxicity, or it may have stored energy such as a pressurised gas.
  • Defining the release conditions. The release conditions may be normal operating conditions, or abnormal conditions. The release path will depend on the failure mechanism, and may be low velocity, high velocity or explosive.
  • Evaluating the effects to personnel and the environment of all end consequences. These may be immediate, delayed or knock-on from the initial event.


Frequency Determination – How likely is it to happen?

The purpose of frequency analysis is to determine the likelihood of each of the undesired events or accident scenarios identified at the hazard identification stage.  There are two basic approaches which are commonly employed in trying to estimate event frequencies.  These are:

  • To use relevant historical data
  • To synthesise event frequencies using techniques such as Fault Tree Analysis and Event Tree Analysis

The two approaches are in fact complementary, each having strengths where the other has weaknesses and hence, wherever possible, it is useful to pursue both approaches.  In this way, the two approaches can be used as independent checks on one another and hence, hopefully, serve to increase confidence in the results. 


Further Modules

The above introductory videos are a taster of the training we can offer on the ESR Technology Major Hazards course. We offer several of the course modules in the form of on-demand/webinar sessions. If you would like further information, please indicate which modules are of interest and complete the contact form below

Hazard Identification
Scenario Representation
HSE - Management Systems
Reliability Definition
Event Tree Analysis
Fault Trees
Bow-Tie Analysis
Data Sources
Human Factors
Milestone Disasters
Safety Integrity Level
Consequence Analysis
Source Terms and Gas Dispersion
Thermal Radiation
Toxic Hazards
Blast Overpressure
Risk Calculation
Risk Criteria and ALARP Demonstration

Would you like us to keep you up to date with services and any future developments with ESR Technology?

Major Hazards Risk Assessment Training Programme

This course is well established and has been delivered by ESR Technology for over 20 years and is used widely as formal major hazards and practical risk assessment training by industrial and regulatory personnel both in the UK and internationally. The course involves formal lectures and interactive syndicate exercises and provides an ideal vehicle for managers and engineers to gain an appreciation of the application of risk assessment techniques and the benefits that may be gained. This course can be presented in its standard form or can be tailored to accommodate any specific requirements of Companies and the delegates.

It is aimed at Engineers and Scientists with a practical interest in the application of risk management and major hazards assessment.

Full Course Duration: 3-5 days (also available as shorter individual modules)

Objectives: The objective of the course are to provide an:

  • Understanding of the risk assessment process
  • Knowledge of tools and techniques for hazard identification
  • Knowledge of tools and techniques for frequency analysis and synthesis
  • An introduction to the modelling of major hazard consequences
  • An understanding of how risks are calculated and issues surrounding their use.

ESR Technology is one of the world’s leading practitioners in the development and application of Safety and Engineering Support Services, having largely pioneered the use of safety engineering and risk assessment techniques across many industries (including the chemical process, oil and gas, power generation, utilities, transport, petrochemical, military and food) and governing bodies both in the UK and internationally.

For more information please contact Terry Atkinson (This email address is being protected from spambots. You need JavaScript enabled to view it.).

Managing Risk During Decommissioning

None of us are getting any younger and that’s just as true for offshore installations. Over the last decade, decommissioning has increasingly become a normal part of business for many operators. This presents numerous challenges, not least of which includes controlling safety and environmental risks on a rapidly changing installation.

ESR Technology, building on our 30-year heritage of major hazards risk assessment for the offshore energy sector, can help you to identify and manage the risks associated with decommissioning and ensure that risks from operations continue to remain ALARP.

We support operators through the complex task of decommissioning in the following areas:

  • Safety Case Preparation
  • ALARP Demonstration at all stages
  • Plugging and Abandonment (P&A) Risk Assessments
  • Safety Input to Decommissioning Programmes
  • SECE Rationalisation and Performance Standard Updates
  • HAZID & ENVID Workshops
  • SIMOPS Workshops
  • COMOPS Notifications & Bridging Documents
  • MAH Risk Assessment (QRA, FERA, TR Impairment, Ship Collisions etc.)
  • Dropped Object Risk Assessment
  • Escape and Evacuation Assessments (EERA)
  • PFEER Compliance
  • Environmental Risk Assessments

 For more information please download our Decommissioning flyer.

Decommissioning Flyer

Conducting Workshops Remotely

COVID-19 has changed how we work. Though, regardless of the workshop or meeting purpose (HAZOP, HAZID, Bow Tie, ALARP, 3D model reviews, training, etc., etc.), we have found a way to make it work.
Here are a few tips we have learned from conducting remote workshops:

  • Be seen, turn on the video camera, non-verbal cues are important!
  • Flip charts, post-it notes, whiteboards – use the online equivalent.
  • A good scribe is more important than ever.
  • Preparation, preparation, and more preparation – share workshop material beforehand.
  • IT systems are like working with children and animals (predictably unpredictable), test it works for everyone beforehand.
  • Frequent breaks to maintain motivation.

For more information please contact Terry Atkinson (This email address is being protected from spambots. You need JavaScript enabled to view it.).

ESR further expands software development capabilities

ESR Technology are very pleased to announce the recruitment of a new Principal Software Developer in our Warrington head office. Ed Walton has re-joined ESR Technology having previously worked at ESR for 6 years after joining the company as a graduate and progressing to become a senior safety and risk consultant.

Ed brings a wealth of experience in software development with particular focus on creating software for mathematical modelling, scientific insight and data visualisation. ESR Technology has more than forty years’ experience in creating software to aid in the application of engineering excellence to demanding projects.

ESR Technical Director Dr Neil Ketchell commented; “The team and I are delighted to welcome Ed back to ESR Technology. ESR has a strong track record in software development which is further strengthened with this appointment. Ed’s experience in enterprise software development coupled with his understanding of Oil and Gas consultancy makes him ideally placed to develop optimal solutions for our clients ”.

The HOIS joint industry project, managed by ESR Technology, shares NDT good practice guidance documents to address energy industry challenges of corrosion under insulation (CUI) and external corrosion of uninsulated components.


HOIS members have approved open publication of two new key documents: HOIS/OGTC Guidelines for in-situ inspection of corrosion under insulation (CUI) and HOIS/OGTC guidance on the inspection for uninsulated external corrosion scabs These documents, rather than being confidential to HOIS members, can now benefit the wider industry and may be downloaded from: www.hoispublications.com.


Corrosion under insulation (CUI) poses a significant operational, safety and economic challenge for the energy industry. The Oil & Gas Technology Centre highlight these headline figures:

  • Corrosion costs the UK economy an incredible £28 billion every year, with that figure rising to £4 trillion globally!
  • Over 20% of the major oil and gas incidents reported within the EU since 1984 are associated with CUI.
  • Many assets in the North Sea are operating beyond their expected design life and 60% of pipe failures are caused by CUI.

The occurrence of CUI is often unpredictable and there is continuing interest in effective inspection/NDT methods to reduce the risk of loss of containment.

The HOIS1 project, supported in this case by the Oil & Gas Technology Centre, highlights the many factors to consider when assessing the applicability of an NDT method for CUI inspection including pipe (or vessel) OD, wall thickness, CUI morphology, the insulation material and thickness as well as the outer cladding (or weather jacket) material and thickness. The guidance document has been developed following an extensive programme of independently assessed blind trials of a range of NDT technologies. It contains a summary of relevant information on CUI within the energy industry. and summarises the main methods currently available (including developmental methods) for NDT. Where available, a summary of performance and reliability information obtained from the HOIS CUI trials is given. Guidance on the application of the methods is given depending on the inspection requirements, including summary tables of methods applicability. Usage of NDT within a strategy for CUI integrity management is also considered and illustrated by case studies, provided by HOIS members, involving successful application of NDT for CUI inspection.

HOIS would like to acknowledge the blind trial participants who invested considerable time, energy and equipment: Acuren, Bilfinger, CAN, Eddyfi, Exxam Systems, GUL, Maxwell NDT/Ether NDE, Oceaneering, Pixel Thermographics, Robinson Research Institute, Russel NDE and Shell and TUV Sonovation. In addition, the Oil &Gas Technology Centre is thanked for their generous co-funding of this work.

External corrosion

External corrosion of uninsulated carbons steel pipework is also a significant problem for energy industry asset owners. As external degradation occurs, corrosion product or scale usually builds up on the affected components to form blisters or scabs. Removal of corrosion product by blasting pressurised live process components has an associated hazard of loss of containment.
In this case, the inspection challenge is to determine the remaining ligament under the corrosion scab. As it is generally not possible to propagate ultrasound through corrosion product; the presence of the scab renders the area of corrosion inaccessible. Hence standard 0° pulse-echo methods are not applicable. Factors that influence the applicability of NDT methods for scab minimum ligament determination include the following:

  • Pipe wall diameter and wall thickness
  • Component geometry
  • Extent of the corroded area in the axial and circumferential directions
  • Accessibility to the corroded area and space around it
  • Surface condition surrounding the corroded area
  • Morphology of the corrosion, especially the presence of highly localised pitting

The HOIS Joint Industry Project started to look at this issue in 2012 and, since then, an extensive series of trials of NDT techniques for inspection of externally corroded un-insulated pipes with the corrosion product in situ has been performed. The most recent trial-based project started in 2017, supported by the Oil & Gas Technology Centre, and was designed to develop and focus the HOIS resources and capabilities for conducting rigorously controlled independent evaluation trials and to compare different inspection methods for these challenging problems. The most recent trials comprised further M-skip scans of additional manufactured components, dual frequency eddy currents, pulsed eddy currents and the GUL QSR1 system.

The trial report is confidential to HOIS members however, the results have been used to develop HOIS/OGTC guidance (HOIS-G-028) on the inspection for uninsulated external corrosion scabs. It summarises the main NDT methods currently available and provides, where available, performance and reliability information obtained from the HOIS scab trials. The final section provides guidance on application for the methods depending on the inspection requirements, including summary tables of method applicability. The guidance is intended for areas of external corrosion that have been located by other means (e.g. visual inspection) for which removal of the corrosion product or scale is hazardous. The component material is limited to carbon steel and the degradation type is limited to loss of wall thickness due to corrosion.


[1] HOIS (www.hois.co.uk) is a well-established joint industry project, managed by ESR Technology, which has been running for more than thirty five years with project partners in the energy sector including asset owner/operators, non-destructive testing service companies, NDT equipment vendors, The Oil & Gas Technology Centre and regulatory authorities such as the HSE. The HOIS vision is to improve the effectiveness of in-service inspection for the energy industry.

Current active HOIS projects include:

  • Determination of remaining thickness under external corrosion scabs: scab characteristics and advanced NDT methods
  • Digitalisation in Oil and Gas
  • Assessment of NDT techniques for carbon and low alloy steel heat exchanger tubing inspection
  • Ultrasonic NDT for NII at elevated temperatures
  • Flange face corrosion recommended practice: updated an extension to include RTJ flanges
  • Optimisation of PEC Technique for CUI – by open trials and modelling
  • Corrosion mapping for small bore pipework
  • Development of a Remote Digital Visual Inspection RP for unmanned pressure vessel IVI (akin to HOIS-RP-103)

Contact This email address is being protected from spambots. You need JavaScript enabled to view it. or This email address is being protected from spambots. You need JavaScript enabled to view it. for more information.



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