The criterion of intrinsic safety for inductive break-sparks

The Safety in Mines Research Establishment, in co-operation with the E.R.A., has made a systematic study of the relative ease of ignition by break-sparks of various flammable gases and vapours, together with an investigation of the basic principles involved. A review of the test methods and of the characteristics of the test apparatus is given, as well as a description of the characteristics of break-sparks and of the relationship between these and the ignition characteristics of the discharges. The circuit parameters affecting the incendivity of break-sparks are also discussed. The principles of gas classification on the bases of minimum igniting current and also of chemical composition are described. It has been possible to adopt the latter method as a result of the steady accumulation of basic data, and this has resulted in the inclusion recently in B.S. 1259 of a very large number of gases and vapours without having to test them individually.