Following the completion of our third successful major CDOIF assessment, we were recently approached by one of our existing clients if they are now required to complete a review, ahead of their scheduled review, following the issuing of new guidance around the COMAH regulations.
Published in September 2026, the CDOIF’s (Chemical and Downstream Oil Industries Forum) new guidance, ‘Major Hazard Human Harm Risk Assessment (MHHHRA) for COMAH’, marks an important development in the assessment of major accident risks across the COMAH sector. The collaboration of these new changes began in 2021 through the CDOIF Risk Assessment Working Group collectively representatives and Regulators throughout the sector.
The guidance (The guidance is applicable to all Control of Major Accident Hazards operators) provides more of a consistent methodology for suitably assessing fatalities and serious permanent injury or health effects from major accident hazards at COMAH establishments.
The guidance provides all key duty holders to work in line to manage major hazard risks. It covers four areas: Hazard Scenario Identification, Risk Analysis, Risk Assessment and demonstration of good practice and that remaining risks are as low as reasonably practicable (ALARP).
Existing site reports may provide a good foundation for application into CDOIF MHHHRA. However, this does not mean CDOIF risk assessments should be reviewed and revised as a matter of course. The new CDOIF MHHHRA guidance could identify gaps in a site’s existing COMAH human-harm assessment, even where its environmental risk assessment has been completed correctly.
Consider a chemical storage site holding a substance classified as very toxic to aquatic organisms, but which also has hazardous properties for people. An environmental CDOIF assessment may correctly identify the substance as presenting a significant pollution hazard, assess the pathways to a nearby watercourse and evaluate the potential for a MATTE.
However, that environmental assessment does not, by itself, establish that the human-harm risks have been adequately assessed. The MHHHRA review should separately consider questions such as:
- Could a loss of containment create a toxic vapour cloud, aerosol or airborne exposure hazard?
- Could workers, emergency responders or members of the public be exposed?
- Could a spill, fire or chemical reaction generate hazardous decomposition products?
- Could a major release cause serious injury or lasting health effects, even if fatalities are unlikely?
- Have credible release scenarios, exposure pathways, safeguards and consequences been adequately identified and assessed?
The precise hazards depend on the substance’s properties, its storage conditions and the credible accident scenarios. Aquatic toxicity alone would not establish a human inhalation or contact hazard; the substance’s safety data sheet and other relevant toxicological information must be examined. We would therefore advise separating the two assessments but use the environmental assessment as an important source of information for the human-harm review for completion of the COMAH risk assessment.