Equipment and protective systems intended for use in explosive atmospheres.

An atmosphere made up of a mixture of air and a combustible substance can be ignited, under certain conditions of temperature and concentration, by a spark or an electric arc, by an object or part of an object heated to a high temperature, by a mechanical spark or by the sudden release of static electrical charges accumulated on insulating or insulated materials.

Electrical and non-electrical equipment intended for use in such atmospheres must therefore be specially designed to avoid creating these different sources of ignition.

The solutions adopted to make equipment safe depend on the state of the flammable substance and its nature.

Rules for the construction of electrical equipment for use in potentially explosive atmospheres are set out in the EN 60079 series of standards, which recently replaced the former European standards EN 50014 to 28 and EN 50281-1-1.

Our ambition in this dossier is twofold:

• enable readers who are not familiar with the standards to gain a fairly precise idea of the solutions adopted to protect equipment against the risk of explosion, and of the constraints that these solutions may entail;

• clarify the consequences of certain provisions for readers who have already read or are familiar with the standards, which may not be readily apparent to a person unfamiliar with these techniques.

In order to better achieve these aims, the construction rules quoted follow scrupulously the order in which the contents of each of the standards commented on are presented. This in no way dispenses with the need to possess the standards in order to design equipment and prove its compliance with the requirements of Annex II of ATEX Directive 94/9/EC. Readers wishing to disregard the standards would be in serious trouble.