Definitions

An explosive atmosphere is a mixture, under atmospheric conditions, of air and one or more dangerous substances – in the form of gases, vapours, mists or dusts – in which, after ignition has occurred, combustion spreads to the entire unburned mixture.

This can be any substance or preparation which, because of its properties or the way it is used, could cause harm to people from fires and explosions. Dangerous substances include: petrol, liquefied petroleum gas (LPG), paints, varnishes, solvents and dusts which – when mixed with air – could cause an explosive atmosphere. Dangerous substances can be found, in varying quantities, in most workplaces. See the Dangerous Substances and Explosive Atmospheres Regulations 2002. Approved Code of Practice and guidance for a detailed definition of dangerous substances.

This is an atmosphere which could become explosive due to local and operational conditions. These would include maintenance activities and fault conditions (such as leakages), and is defined within the EPS Regulations.

Regulation 7 of the Dangerous Substances and Explosive Atmospheres Regulations 2002

• Zone 0: A place in which an explosive atmosphere – consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist – is present continuously, for long periods, or frequently
• Zone 1: A place in which an explosive atmosphere – consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist – is likely to occur in normal operation occasionally
• Zone 2: A place in which an explosive atmosphere – consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist – is not likely to occur in normal operation but, if it does occur, will persist for a short period only
• Zone 20: A place in which an explosive atmosphere – in the form of a cloud of combustible dust in air – is present continuously, for long periods, or frequently
• Zone 21: A place in which an explosive atmosphere – in the form of a cloud of combustible dust in air – is likely to occur in normal operation occasionally
• Zone 22: A place in which an explosive atmosphere – in the form of a cloud of combustible dust in air – is not likely to occur in normal operation but, if it does occur, will persist for a short period only

There are two equipment groups defined in the EPS Regulations:

• Equipment group I: Equipment intended for use in underground parts of mines, and to those parts of surface installations of mines, liable to be endangered by firedamp and / or combustible dust
• Equipment Group II: Equipment intended for use in places, other than those specified for Equipment Group I, liable to be endangered by explosive atmospheres

Under ATEX 95, equipment is categorised as follows:

• Mining equipment -
  • Group I, category M1: Very high level of protection; equipment may continue to operate in the presence of explosive atmosphere
  • Group I, category M2: High level of protection; equipment to be de-energised in presence of explosive atmosphere
• Non-mining equipment -
  • Group II, category 1: Equipment suitable for Zones 0, 20
  • Group II, category 2: Equipment suitable for Zones 1, 21
  • Group II, category 3: Equipment suitable for Zones 2, 22