A1      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.

A2      DSEAR code of practice L138 gives a detailed definition of a ‘dangerous substance’ which should be referred to for more information. It includes 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.

A3      This is an atmosphere which could become explosive due to local and operational conditions. These would include maintenance activitites and fault conditions such as leakages.

A4      Regulation 7 of DSEAR requires employers to classify places at the workplace where explosive atmospheres may occur into hazardous and non-hazardous areas. Hazardous areas are classified into zones, these are:

• 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 or 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 or 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.

A5      There are two equipment groups defined in the EPS Regulations. Equipment Group I is 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 is equipment intended for use in places, other than those specified for Equipment Group I, liable to be endangered by explosive atmospheres.

A6      Under ATEX 95 equipment is categorised as below:

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