SIST EN 50303:2000

Group I, Category M1 equipment intended to remain functional in atmospheres endangered by firedamp and/or coal dust

1.1   This standard specifies the design, construction, testing and marking requirements for Group I, Category M1 equipment intended to remain functional in underground parts of mines, as well as those parts of surface installations of such mines endangered by firedamp and/or coal dust clouds under normal atmospheric conditions of pressures ranging from 0,8 bar to 1,1 bar and temperatures ranging from   20 °C to + 60 °C.
1.2   It applies to all electrical and non-electrical equipment capable of causing an explosion through its own potential source of ignition.
1.3   It also applies to cables, pipes and optical fibres, when such items are used to carry energy sources and form part of equipment intended to remain functional in an atmosphere endangered by firedamp and/or coal dust.
1.4   It does not apply to category M1 Miners' Caplights, which are dealt with in prEN 62013-1 (in preparation).
NOTE 1   As the energy needed to ignite a coal dust /air cloud is in excess of 600 times* that needed to ignite a firedamp /air mixture, this standard assumes that provided intrinsically safe 'ia' circuits are constructed to be safe in an explosive atmosphere of firedamp /air, then such circuits are not capable of directly igniting an explosive atmosphere of coal dust/air.
* Based on tests performed by several member state laboratories. Verified at the UK Health & Safety Laboratories, Buxton - Report by Dr P. Tolson, dated 9 August 1995 -  "Ignition of coal dust/air mixtures using a modified IEC spark test apparatus".
NOTE 2   In designing equipment for operation in explosive atmospheric conditions other than those given in 1.1 above, this standard may be used as a guide. In such cases, additional testing is recommended to allow the manufacturer to be able to demonstrate that the equipment is suitable for the exceptional conditions of use.
NOTE 3   When an explosive firedamp atmosphere occurs in the underground workings of a mine, or at a surface installation, it is imperative that the ignition risk be kept to a minimum. Member State Governments may therefore prohibit the continued use of certain Category M1 equipment in an atmosphere endangered by firedamp and/or coal dust if it is not necessary for it to remain functional for the protection of workers**.
** This has its origin in clause 5.1 of the proposals to the Governments of members States adopted by the Safety and Health Commission for Mining and Other Extractive Industries (SHCMOEI) at its meeting on 29.10.1986. Document No 6374/13/82 - "Electrical apparatus and systems for use when the concentration of firedamp exceeds the statutory limit for electricity".