Electrical equipment in potentially explosive atmospheres. Intrinsic safety

In many industrial installations, the substances used are flammable, and can take the form of gas, vapour, mist or dust. When mixed with air, these substances form an explosive atmosphere, in which equipment, particularly electrical equipment, must be able to operate.

To ensure the safety of people and installations, such equipment must comply with strict, tried-and-tested rules to minimize the risk of explosion. There is a body of regulations and standards governing the construction and use of electrical equipment for potentially explosive atmospheres.

In Europe, the basic regulatory texts are European Community Directives, which are transposed into national law in the form of decrees and orders. Standards are issued by the European bodies CENELEC and CEN. These standards are reproduced identically in national standards.

In the U.S. and Canada, regulatory texts are equivalent to Codes, which define rules for the installation of electrical equipment. Standards are published by various semi-public or private organizations and validated by public bodies.

Normative texts provide for various ways of ensuring safety, known as "protection modes", the main aim of which is either to prevent ignition and explosion from spreading, or to ensure that the probability of these phenomena occurring is negligible (of the order of 1 · 10 ^{– 3} ).

The "intrinsic safety" (IS) protection mode is the one in which this very low probability of ignition is achieved.

This article includes a section devoted to regulations, presented before the technical sections, in order to clarify the basics of the technical rules. These technical sections explain what IS equipment is, how it should be designed and built, and how it should be installed and used.