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Page revision date -  4 September 2021

Risk assessment is a mandatory requirement in law.  It doesn’t matter how complex a facility is, or how big the hazard, the basic framework by which risk assessment is carried out is the same: what varies is the depth of analysis that is required to make the risk assessment proportionate to the risk.

  • Risk is the chance, high or low, of somebody or something being harmed by the hazard, and how serious the harm could be.

  • A hazard is anything that may cause harm, eg chemicals, electricity, working from ladders, noise etc.

HSE guidance breaks down the basic framework of risk assessment into 5 steps [1].  These are given in Table 1 below together with a description as to how we at COMAH Consulting Ltd deal with those steps when dealing with process / chemical type plants:



Risk assessment should be carried out by a person or persons who can demonstrate competence [2].  Competence can be described as the combination of training, skills, experience and knowledge that a person has and their ability to apply them to perform a task safely [2]. 

At COMAH Consulting we have consultants who are competent to carry out process related risk assessment for even the most complex of facilities.  Also, we know what you need to do to be assured of our competence [2] and we can help you with that.

Help and Support

If you would like to discuss a risk assessment challenge that you face please contact us for a no obligation discussion and we will try and help you.

For more information of risk assessment and the legal requirements, see the HSE website 'Risk Management' mini-site and section on frequently asked questions [3]. 





Risk Assessment Step and Description
How COMAH Consulting does this in the chemical / process industry when dealing with Major Accident Hazards?


Identify the hazards

We carry out structured and systematic hazard identification studies.  For example HAZID, HAZOP, FMEA, Safety Critical Task Analysis, and “What if ?”Study. 

Question: How does one know what technique(s) to use?

Answer:  It requires judgement.  A competent person [2] needs to select techniques which provides a depth of challenge and scrutiny that is proportionate to the risk that the facility presents.


Decide who might be harmed and how

This requires consequence estimates of one form or another.  Sometimes all that is warranted is a consensus from experienced personnel based on their experience.  Sometimes complex consequence modelling calculations are required which estimate numbers of people who could be killed and injured and the physical extent and persistence of environmental harm. 

Question: How does one know which technique to use?

Answer:  It requires judgement.  A competent person [2] needs to select the depth of analysis so that it that is proportionate to the risk that the facility presents.  The bigger the hazard and the more frequently it may occur then the greater is the understanding required of the potential consequences. This means some iteration may be required as part of the risk assessment process.


Evaluate the risks and decide on precautions

The estimated risk must be compared to risk tolerability criteria.  Precautions (engineered or human) need to be in place until the risk is as low as is reasonably practicable (ALARP).  In most cases, this can be based on written “relevant good practice", but sometimes it can only be determined and sufficiently demonstrated by quantification of an appropriate conservative hazard scenario.  We typically model the consequences of the scenario using 'DNV PHAST' and we model the likelihood of the scenario using using a variety of equipment failure rate data sources, e.g. OREDA and Faradip3.

Question: How does one know what evaluation technique to use?

Answer:  It requires judgement.  A competent person [2] needs to select a means of demonstration that is proportionate to the risk that the facility presents.  The bigger the hazard and the more often it may occur then the greater is the depth required in the demonstration.  LOPA can be a useful means of recording a risk assessment.


Record your significant findings

We use reports, tables and diagrams to communicate this information.  Our risk assessment is a demonstration that the law is complied with. 


Review your assessment and update if necessary

This is normally triggered by any changes to the plant or after a certain time period has elapsed. The review process should be determined on a case by case basis, after consideration of specific factors (such as change management, and routine process reviews etc.)