The Major Hazard Human Harm Risk Assessment — MHHHRA — is the most significant development in COMAH safety report practice in years, and the clock is already ticking for sites that need to get ahead of it.
Developed by CDOIF (the Chemical and Downstream Oil Industries Forum), MHHHRA provides a comprehensive framework for demonstrating sufficient MAH risk assessment within COMAH Safety Reports. While formal publication is imminent, HSE are already signalling their expectations clearly — in industry forums and in COMAH Safety Report pre-receipt meetings — that the MHHHRA approach should be followed now. It is shaping up to be the definitive standard for predictive human harm assessment in Safety Reports, in the same way that CDOIF’s Environmental Risk Tolerability for COMAH Establishments has become the benchmark for Safety Report environmental MATTE assessment.
In short: if your site is due a Safety Report submission or review, MHHHRA compliance is something you need to be planning for today.
What MHHHRA Actually Requires
The guidance is substantial. At its core, it demands a structured, evidence-based approach across four interconnected stages:
Identification — A screening table capturing your full set of MAHs, grouped into intuitive areas and collated under representative scenarios where applicable.
Analysis — For each representative scenario: detailed consequence analysis (including consequence modelling), a clear basis of safety, fault and event tree combinations covering initiating causes and consequence outcomes, identification of relevant good practice, evaluation of control measures, and quantified scenario likelihoods — along with any identified risk gaps.
Assessment — Cumulative risk evaluation across all MAH top event scenarios for all equipment, considering exposure for different job functions and for on-site and off-site population groups.
Further Measures and ALARP — Tolerability judgements based on cumulative individual and societal risk, with identification of any further risk reduction measures required.
This is a demanding and multi-disciplinary exercise. Done properly, it draws on consequence modelling, fault and event tree analysis, good practice benchmarking, and quantitative risk assessment — all presented coherently within a safety report structure that will satisfy HSE scrutiny.
Why OTECSA?
OTECSA has been working with clients on MHHHRA-compliant risk assessments since the guidance emerged, and we are already well-versed in what it takes to get this right.
Our team brings together the full range of process safety disciplines that MHHHRA demands — consequence modelling, bow-tie and fault tree analysis, LOPA, ALARP demonstration, and safety report writing — under one roof. We don’t just understand the technical requirements; we understand how to structure, organise, and present MHHHRA assessments in a way that gives both your team and HSE confidence in the outcomes.
Crucially, we also know where the gaps tend to appear. Pulling together the many elements of a MHHHRA assessment — across different scenarios, equipment types, and risk groups — is complex, and it’s easy to find that existing data, models, or studies don’t fully cover what’s needed. OTECSA can identify those gaps early and help you fill them efficiently, avoiding costly surprises late in the process.
Whether you are starting from scratch, updating an existing safety report, or preparing for a pre-receipt meeting with HSE, OTECSA has the expertise to guide you through every stage of MHHHRA implementation.
Get in touch today to discuss how we can support your MHHHRA assessment — and make sure your site is ready.