The site Operator should specify the types and quantities of explosives that could be present at each location at the installation. This information will determine whether the installation falls within the remit of COMAH and, if so, whether the installation is to be classed as a lower-tier or top tier site. For this purpose the explosives on site need to be partitioned into two risk groups, known as R2 and R3, and the quantities of each determined.
R2 explosives comprise:
R3 explosives comprise:
R3 substances are those which are either as sensitive or more sensitive to impact and friction than RDX. An indicative list of explosives falling into this category is shown in Table A1.1.
| Explosive type | Substance/preparation | Risk phrase |
|---|---|---|
|
Ammonium Picrate |
Substance |
R21 |
|
Ammonium Perchlorate |
Substance |
R2 |
|
ANFO, emulsion, slurry, water gel, explosives |
Preparation |
R2 |
|
Barium Azide |
Substance |
R3 |
|
Black Powder |
Preparation |
R2 |
|
Cast Explosives |
Preparations |
R2 |
|
Casting liquids |
Preparations |
R3 |
|
Casting Powders |
Preparations |
R3 |
|
Ethylene Glycol Dinitrate |
Substance |
R3 |
|
Hexanitrostilbene |
Substance |
R3 |
|
Hexolite (Hexotol) |
Substance |
R2 |
|
HMX Dry |
Substance |
R32 |
|
HMX (Desensitized by addition of water or Phlegmatizer |
Preparation |
R22 |
|
Lead Azide |
Substance |
R3 |
|
Lead Styphnate |
Substance |
R3 |
|
Mercury Fulminate |
Substance |
R3 |
|
NG Gelatines |
Preparation |
R3 |
|
NG Powders |
Preparation |
R2 |
|
Nitrocellulose |
Substance |
R3 |
|
Nitroglycerine |
Substance |
R3 |
|
PETN |
Substance |
R3 |
|
PETN/WAX |
Preparation |
R3 |
|
Plastic explosive |
Preparation |
R2 |
|
Primary explosives |
Preparation |
R2 |
|
Pyrodex |
Preparation |
R3 |
|
RDX (Dry Pure) |
Substance |
R32 |
|
RDX (Desensitized by addition of water or Phlegmatizer |
Preparation |
R22 |
|
Single/double/triple base propellant |
Preparation |
R3 |
|
Tetrazene |
Preparation |
R3 |
|
Trinitrobenzene |
Substance |
R23 |
|
Trinitrophenol (Picric Acid) |
Substance |
R23 |
|
Trinitoresorcinol (styphnic acid) |
Substance |
R23 |
|
Trinitrotoluene |
Substance |
R2 |
|
Trinitrotriazalone |
Substance |
R2 |
Notes: Pyrotechnic compositions (mixture of substances) and articles containing explosive or pyrotechnic substances/preparations are included as explosives of Category 4 in schedule 1 part 3 of the COMAH regulations (Note 2(a)) and are subject to the same threshold quantities as R2 substances and preparations.
In addition to explosives, the Operator should identify any other dangerous substances on site. The dangerous substances to which the regulations apply and the threshold limits to be applied are listed in Schedule 1 of the regulations. For the majority of explosives establishments the dangerous substances likely to be involved are shown in Table A1.2.
| Category of dangerous substances | Lower tier limit (tonnes) | Top tier limit (tonnes) |
|---|---|---|
|
Ammonium Nitrate |
350 |
2,500 |
|
Ammonium Nitrate1 |
1,250 |
5,000 |
|
1. Very Toxic |
5 |
20 |
|
3. Oxidising |
50 |
200 |
|
4. R2 Explosives |
50 |
200 |
|
5. R3 Explosives |
10 |
50 |
|
6. Flammable Liquids |
5,000 |
50,000 |
|
7. Highly Flammable Liquids2 |
50 |
200 |
|
8. Extremely Flammable Liquids |
10 |
50 |
Notes:
Note 1: Ammonium nitrate based fertilizers complying with the Fertilizer Regulations 1991 and composite fertilizers.
Note 2: Higher limits exist for highly flammable liquids with a flash point of less than 21°C which do not themselves qualify as extremely flammable.
An aggregation rule applies where combinations of dangerous substances are present below their threshold limits. The dangerous substance categories listed in the above table, with the exception of substances in the VERY TOXIC category, are aggregated in accordance with the rule described in Schedule 1 of the Regulations in order to determine the total quantity of qualifying substances present.
Dangerous substances at an establishment in quantities of not more than 2% of the relevant qualifying quantity should be ignored for the purposes of calculating the total quantity present, provided their location is such that it cannot act as an initiator of a major accident elsewhere on site. This 2% rule will only apply where the total quantity present at one location within the establishment is equal to or less than 2% of the relevant qualifying quantity.
Example: In calculating the total quantity of dangerous substances present at a potential Top Tier site, a magazine containing 4 tonnes of blasting explosives (2% of the Top Tier limit for explosives in Category 4) may be excluded for the calculation aggregating the total quantity, provided its location is such that it cannot initiate a major accident elsewhere on site.
Whether the explosives in a magazine or process building could initiate another major accident depends upon the nature and construction of the receptor (i.e. other magazines, tanks containing flammable or toxic liquids, stocks of oxidizers, etc.) and the characteristics of the donor building itself (e.g. the type and quantity of explosives present, the construction of the magazine or process building and mounds).
The requirement to prevent the initiation of another major accident elsewhere on site is not restricted to instantaneous communication but includes delayed events, e.g. secondary fires caused by an explosion leading to a second explosion. It should be noted that the internal separation distances required by the explosive licence are intended to prevent instantaneous communication but these distances will not ensure delayed secondary events are prevented. For these reasons it is not possible to lay down general rules regarding what will and what will not initiate a major accident elsewhere on site and the Operator will need to make an individual assessment of the specific circumstances for each case where the 2% rule is to be applied.
The rule is only relevant for the purposes of calculating the extent to which the regulations apply; all dangerous substances present must be considered when preparing the major accident prevention plan or safety report.
Examples:
An establishment holding 40 tonnes of explosives and 200 tonnes of ammonium nitrate will be aggregated as follows:
40/50 + 200/350 = 1.37 i.e. Lower Tier
but
40/200 + 200/2500 = 0.28 not Top Tier.
A factory holding 500 tonnes of AN, 150 tonnes of explosives, 1.5 tonnes of primary explosive (Category 5, Risk Phrase R3) and 10 tonnes of sodium and calcium nitrate will be at least Lower Tier and on aggregation becomes Top Tier as follows:
500/2500 + 150/200 + 1.5/50 + 10/200 = 1.03
(If the stock of R3 explosives is reduced to 1 tonne and located so that it could not initiate a major accident elsewhere on site, then the calculation becomes:
500/2500 + 1500/200 + 10/200 = 1.00
Since the quantity of R3 explosives present equals 2% of the qualifying quantity, it can be ignored for the purposes of this calculation. The factory is then a Lower Tier site).
It is important to note that the quantity to be used in any calculation of this type is the quantity the Operator envisages being on site at any one time, NOT THE TOTAL QUANTITY ALLOWED BY THE EXPLOSIVES LICENCE, e.g. if it is envisaged that a magazine will never hold in excess of either lower threshold limits for explosives then the regulations will not apply, even if the quantity allowed by the licence is in excess of these limits. However, should the Operator subsequently wish to make use of the excess capacity and hence exceed a qualifying limit (either into Lower Tier or from Lower to Top Tier), the site will be regarded as a new establishment and the requirements for the relevant notification, major accident prevention plan and/or safety reports will need to be complied with, before the increase is made.
Explosives containing more than 7% of nitroglycerine (NG) and/or ethylene glycol dinitrate (EGDN) are assigned to the very toxic category as well as being explosives. Where substances and preparations fall into two categories they are regarded as being in the category that has the lowest threshold. Therefore, explosives containing more then 7% of NG/EGDN are treated as "Very Toxic", but only for the purposes of determining the application of the regulations. Thus COMAH will not apply to a magazine holding 49.9 tonnes of water based blasting explosives and 4.9 tonnes of NG based explosives because Explosives and Very Toxic substances are not aggregated together.
Public Register of COMAH Establishments
