As our principal HAZOP consultant, Russell has a varied and plentiful experience as an IChemE trained HAZOP leader.  As a key part of our consultancy services to our clients, he has carried out HAZOP studies in a wide range of industry sectors and for various major hazard regimes (including COMAH, 'sub-COMAH', DSEAR, and pipeline safety). 

HAZID (Hazard identification) , HAZOP (Hazard and Operability Study):

These terms describe some of the common techniques for identifying major hazards for the purpose of determining the route to performing the detailed major hazard risk assessments and the demonstrations of compliance with the legal requirements.   The studies are recognised tools for identifying hazards in a structured, systematic and robust way.  The techniques may be used to identify or validate hazard types for new or replacement plant / equipment, and also for modifications to existing plant or additional units.

The UK Health and Safety Executive (HSE) describe 6 stages of hazard identification as illustrated below in Table 1:


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A short description of the HAZID study technique

Many organisations carry out the hazard identification study with a multi-disciplinary team using 'hazardous event' guidewords as prompts to structure and focus the discussion.  The hazard study leader (sometimes simply termed 'HAZOP leader') of the team splits the plant up into component blocks that are appropriate for the study.  The HAZOP leader then challenges the team to think of how a 'hazardous event' (based on the guidewords) could occur.  Typical event-types are, for example, “Explosion within Equipment”, “Fire External to Equipment”, “Static Electricity Discharge”.  There may often be up to 20 'hazardous event type' prompts used in a study. For each 'hazardous event', the team records information about the 'cause', 'consequence' and 'safeguards'.  The team also use their judgement to decide if further information is needed or if additional safeguards are required. The team will raise 'actions' to deal with these.  Sometimes formal risk assessment is carried out during the HAZID with estimates of severity and frequency  being scored and recorded with and/or without safeguards.  The scoring used complements a risk matrix that is defined in a advance.

The output of the HAZID is a written report.

Summary of a typical methodology that we use

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Last update date - 1 April 2018

A HAZID is very good at systematically identifying all the possible Major Accident Hazards (to people and the environment).  An external HAZOP consultant can add independence to the process, for example by challenging established ways of working against current relevant good practice.

It is not so good at identifying all the possible individual causes of the major accidents. 

Unless the plant being considered is very simple a more detailed technique [like "HAZOP" (HAZOP study stage 3)] is required to systemetically identify all the possible accident casues.

A warning regarding risk assessment:

A HAZID may be used as an explicit risk assessment tool - the likelihood and severity are estimated using a risk matrix and compared to a tolerability criteria.  However, for a hazardous event that has the potential to kill people it is unlikely that this can be adequately risk assessed in a HAZID meeting itself unless a clearly conservative approach is taken or some advance work has been carried out. The reason for this is that event frequency and consequence estimation can take longer than a few minutes to work out.  In a HAZID only a short period of time is given to each scenario.  The main function of the HAZID is to identify hazards rather than to risk assess them.  Common sense is required and the risk assessment needs to be proportionate as explained in the principles of the ubiquitous 5 steps to risk assessment approach recommended by the HSE.  (

An example of a (fictitious/sample) HAZID output record is shown below

HAZID - When to use it
Key considerations for success
Can COMAH Consulting help?
  • When reviewing an existing plant as part of a risk assessment review / up date
  •  At the start of the design for a new project
  • Make sure the HAZOP Study 1 data has been collated so that there is a good foundation for the study.
  • Have an operator on the HAZID team
  • If the team has low experience involve an independent process safety engineer
  • Be clear how the outputs from this study should integrate with other studies/techniques in the overall risk assessment process.
  • Yes!
  • We can provide an experienced HAZID leader and HAZOP leader who will ensure that the scope is appropriate, the foundation documentation sufficient and team experience is adequate.
  •  We can also provide a scribe for the study who can also act as an independent process safety engineer

HAZOP study

Table 1 - HAZOP and HAZID study summary of stages
Identify major hazards and check for availability of key hazard data

Coarse HAZOP using flow-sheet and block diagram

Full HAZOP on frozen P&I diagram

Check that all intended actions have been implemented, including hardware and software

Pre-commissioning check including statutory requirement

Safety audit after a few months operation

HSE HAZOP Stages (Source: