Carrying out COMAH calculations seems simple, but can be a daunting task when you start reading the legislation. Here we answer some frequently asked questions regarding COMAH tier calculations. Often COMAH calculations are the first step on the COMAH and MHHHRA journey.
What is the difference between lower tier and upper tier COMAH?
Both tiers are set by the quantity of dangerous substances present at an establishment. Lower tier applies once the lower qualifying quantity in Schedule 1 is met. Upper tier applies at the higher threshold and brings additional duties, most notably the requirement to produce a Safety Report.
What is the 2% rule in COMAH?
The 2% rule lets you ignore dangerous substances held in quantities of 2% or less of the relevant qualifying quantity. It only applies where their location means they cannot act as an initiator of a major accident elsewhere at the establishment, so it is a test of location as much as volume.
How does the COMAH aggregation rule work?
Each substance is expressed as a fraction of its qualifying quantity and the fractions are added together. If the total reaches 1, the threshold is met. The calculation is done three times, separately for health, physical and environmental hazards, against both lower and upper tier quantities.
Do I need to add up different hazard types together?
No. Hazard types are summed separately rather than combined into one figure. Health, physical and environmental hazards each get their own calculation, and if any one of the three reaches 1 the site falls within scope at that tier.
Does COMAH apply to distilleries and anaerobic digestion plants?
It can. Whisky maturation warehouses hold significant quantities of flammable liquid, and anaerobic digestion plants generate flammable gas on site. Both sectors regularly need a formal tier calculation, and both are areas where OTECSA has carried out recent assessments.
