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Ammonium nitrate and COMAH

For more information about the Control of Major Accident Hazards Regulations 1999 (COMAH), see HSE’s dedicated COMAH web pages.

Ammonium nitrate is a named dangerous substance in COMAH and has set qualifying quantities for different types (fertiliser, technical, off spec), which govern whether a site is classed as sub-COMAH, lower-tier or top-tier COMAH.

Extracts from COMAH Schedule 1, Part 1 for ease of reference. 

Extract Lower tier (tonnes) Top tier (tonnes)
Ammonium nitrate, fertilisers capable of self-sustaining decomposition
Ammonium nitrate-based compound/composite fertilisers (compound or composite fertilises containing ammonium nitrate with phosphate and/or potash) in which the nitrogen content as a result of the ammonium nitrate is: between 15.75% and 24.5% by weight and either with not more than 0.4% total combustible or organic materials or which satisfy the detonation resistance test described in Schedule 2 to the Ammonium Nitrate Materials (High Nitrogen Content) Safety Regulations 2003 ‘the detonation resistance test’ or 15.75% or less by weight and unrestricted combustible materials
5 000 10 000
Ammonium nitrate, fertiliser grade
Straight ammonium nitrate-based fertiliser and ammonium nitrate-based compounds/composite fertilisers in which the nitrogen content as a result of ammonium nitrate is: more then 24.5% by weight, except for mixtures of ammonium nitrate with dolomite, limestone and/or calcium carbonate with a purity of at least 90% more than 15.75% by weight for mixtures of ammonium nitrate and ammonium sulphate or more than 28% by weight for mixtures of ammonium nitrate with dolomite, limestone and/or calcium carbonate with a purity of at least 90% and which satisfy the detonation resistance test.
1 250 5 000
Ammonium nitrate, technical grade
Ammonium nitrate and preparations of ammonium nitrate in which the nitrogen content as a result of the ammonium nitrate is: between 24.5% and 28% by weight, and which contain not more than 0.4% combustible substances or more than 28% by weight, and which contain not more than 0.2% combustible substances Aqueous ammonium nitrate solutions in which the concentration of ammonium nitrate is more than 80% by weight.
350 2 500
Ammonium nitrate, ‘off spec’ materials and fertilisers not satisfying the detonation resistance test
Material rejected during the manufacturing process and ammonium nitrate and preparations of ammonium nitrate, straight ammonium nitrate-based fertilisers and ammonium nitrate-based compound/composite fertilisers that are being or have been returned from the final user to a manufacture, temporary storage or reprocessing plant for reworking, recycling or treatment for safe use. Fertilisers which do not satisfy the detonation resistance test, other than fertilisers which: at the time of delivery to a final user satisfied the detonation resistance test but later become degraded or contaminated and are temporarily present at the establishment of the final user prior to their return for reworking, recycling or treatment for safe use or to their being applied as a fertiliser.
10 50
Updated 2011-10-20