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The following measures apply to all processes and operations.

The COMAH Regulations apply to establishments holding dangerous substances above certain quantities.

The hazardous substances and mixtures are classified in the European Regulation (EC) No 1272/2008 on classification, labelling and packaging of substances and mixtures (CLP).

1. You must work out if the COMAH regulations 2015 apply to your activities. This will depend on the quantity of dangerous substances you store on site.

The aggregation rule

2. To work out if the COMAH regulations apply to your activities, you must apply the aggregation rule. This involves adding together quantities of all the dangerous substances held at your site.

3. If you store any individual hazardous substance (or mixtures) at quantities lower than the relevant threshold, you must add together the partial fractions of their threshold quantities. If the total equals or exceeds 1, the COMAH regulations apply.

4. You only add together quantities of substances with similar hazards, so all oxidising, explosive and flammable substances are added together. Para 381 of COMAH guidance (L111) contains further details.

5. If the quantities of dangerous substances you store may fluctuate, you must base your calculation for the aggregation rule on the maximum quantities you could have on site during normal activities. This covers seasonal variations, deliveries or fluctuations in demand.

6. Category 1 and 2 flammable gases have a lower tier COMAH threshold of 10 tonnes. If your site stores less than 10 tonnes, you must apply the aggregation rule.

Upgraded biogas

The qualifying threshold in tonnes is 50te for lower tier (LT) and 200te for upper tier (UT) COMAH.

Biogas is aggregated with other flammable gases or liquids, such as liquid petroleum gas (LPG, propane or butane) or diesel. These have individual lower tier COMAH limits of 50 tonnes and 2500 tonnes respectively. If the aggregation is greater than 1 then COMAH applies.

Here are 2 examples.

Example 1: injecting gas to the grid

AD sites which inject upgraded biogas to the national gas grid need to consider the quantity of both the:

• biogas in the headspaces and storage facilities on site
• liquefied flammable gases stored

For example:

8 tonnes of raw biogas (lower tier limit is 50)

25 tonnes of LPG (lower tier limit is 50)

5 tonnes of sulphuric acid (lower tier limit is 50)

Aggregation for the COMAH assessment is:

8 50 = 0.4

25 50 = 0.5

5 50 = 0.1

0.4 + 0.5 + 0.1 = 1.0 0.0

As this figure adds up to 1 the COMAH regulations apply.

Example 2: biogas burnt on site to generate electricity

AD sites which use gas to generate electricity, with a store of diesel for back-up generators, would need to consider the quantity of both the:

• biogas in the headspaces and storage facilities on site
• diesel stored

For example:

9.4 tonnes raw biogas (lower tier limit is 10)

600 tonnes diesel (lower tier limit is 2500)

Aggregation for the COMAH assessment is:

9.4 10 = 0.94 600 2500 = 0.240.24 + 0.94 = 1.18

As this figure is above 1 the COMAH regulations apply.

Operators should contact the HSE for more information on COMAH.