10 - Apparatus using protection concept flameproof enclosure ‘d’: (BS/EN 50018 (1995))

Abstract

This chapter focuses on flameproof enclosure, which is probably the oldest of the protection concepts considered in the UK and Europe as suitable for Zone I and less hazardous areas dating back to before the Second World War. It is one of the only three protection concepts accepted for Class 1 Division 1 in the USA, which is the equivalent of Zone 0 and 1. The development of the flameproof enclosure followed very quickly upon the development of usage of electricity in coal mines and the recognition that rotating electrical machines, which were all dc in the early part of the twentieth century, and produced highly ignition-capable sparking in normal operation. A flameproof enclosure must contain an internal explosion of the worst case explosive atmosphere for which it is designed, without damage. The joints between its parts which access the external atmosphere must be of specified maximum dimensions and its strength must be such that those joints do not widen under conditions of internal explosion of the worst case explosive atmosphere for which it is designed, to a point where the flame is transmitted outside the enclosure and ignites the external atmosphere. The protection concept has been addressed in several Standards applicable in the UK over the years, and the first Standard of significance was BS 229, which was first issued in 1926 with revisions in 1929, 1940, 1946, and 1957. BS 2292 was effectively replaced in 1971 by BS 4683, Part 2 which included many of the ideas at that time being developed in Europe and internationally.