If you run a Lower Tier COMAH site, most of what you’ll read about how you differ from an Upper Tier site is the easy part: no COMAH Safety Report, no off-site emergency plan. Both true, but they miss what actually matters day to day. Your duties are almost identical to an Upper Tier site’s. What changes is how you demonstrate you meet them. This page explains that real difference, the three questions it comes down to for a Lower Tier site, and how a gap analysis of your MAPP and SMS tells you where you stand.

The real difference: it’s the demonstration, not the duties

The headline differences are easy to find, and they’re real: as a Lower Tier site you don’t produce a COMAH Safety Report, and you don’t need an off-site emergency plan. But the underlying duties, preventing major accidents and limiting their consequences, are almost the same as an Upper Tier site’s. The practical difference is how you show it. An Upper Tier site makes its demonstration in a COMAH Safety Report. A Lower Tier site demonstrates compliance through its MAPP and its SMS. So on a Lower Tier site, your MAPP and your safety management system aren’t just paperwork; they are your demonstration.

There are a few other obligations too: you still notify the Competent Authority and hold hazardous substances consent, but those are largely one-off. The ongoing demonstration that you’re preventing major accidents runs through your MAPP and SMS, and that’s where the real, continuing work sits.

The three questions every Lower Tier site should ask

It comes down to three:

COMAH sets out what those elements are, from how you organise and resource safety through to management of change, emergency planning and review. The useful question isn’t whether you can recite the list, it’s whether each one is genuinely there, and good enough.

Having it isn’t the same as it being good enough

Questions 2 and 3 look similar, but they’re not the same, and the gap between them is where many Lower Tier sites fall short. Take management of change. Plenty of sites have a management of change procedure, so on paper the element is covered. Not all of them stand up to the scrutiny a major accident hazard site attracts. That two-level test (do you have a system for it, and is that system good enough for COMAH?) applies to every element of your SMS. Having it is not the same as it being good enough for a major-hazard site.

Where Lower Tier sites frequently fall short

In my experience it’s rarely that nothing exists; it’s that what exists wasn’t built with a major accident hazard site in mind. The gaps tend to cluster in the same few places:

Each tends to be a ‘have it, but not good enough for COMAH’ gap rather than a missing one.

Proportionality: how much less can a Lower Tier site legitimately do?

Many sites stay Lower Tier on purpose, often for cost. So the fair question is: what can you legitimately do less of than an Upper Tier site? The honest answer is that it depends far less on your tier than you would think.

Proportionality is what decides how deep your risk assessment has to go, and it is set scenario by scenario, not site by site. It starts with severity, how many people a scenario could kill or seriously injure, counted before your measures are applied, and is then adjusted by the character of the scenario itself. An Upper Tier site that simply stores a lot of a well-understood substance can end up needing a simpler assessment than a Lower Tier site running a complex reaction.

So proportionate doesn’t mean minimal, and it doesn’t mean the same treatment for every scenario. The skill is knowing where you can rightly do less, and where the extra detail is required. Get that judgement wrong in either direction and it costs you, either in effort you didn’t need to spend, or in a gap an inspector will find.

How a Lower Tier gap analysis answers all of this

A gap analysis of your MAPP and SMS against COMAH expectations answers every question above in one exercise. It tells you which elements are covered, what’s missing, what’s present but not yet good enough for COMAH, and where you can safely be proportionate. It covers the full picture: your MAPP, your SMS, and the notification and consent obligations that sit around them. In other words, it turns ‘I think we’re probably ok’ into a clear picture of where you actually stand, and what, if anything, is worth doing about it.

If you’re specifically wondering about MHHHRA

Risk assessment applies to Lower Tier sites too, and MHHHRA is a common question. If that’s what’s on your mind, start with MHHHRA for Lower Tier Sites. For the risk assessment itself, see COMAH Risk Assessment. For the full picture of COMAH support, see COMAH Consulting.

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