Correlation of ignitabilities of gases and vapours by a break spark and at a flange gap

The object of the study was to investigate a possible correlation between the relative ignitabilities of gases and vapours by electric break sparks and at gaps between the flanges of equipment enclosures, and to assess whether the scope of British Standards BS 229 (Flameproof enclosure of electrical apparatus) and BS 1259 (Intrinsically safe electrical apparatus and circuits) could, in consequence, be extended. Comparisons were therefore made between the minimum igniting currents (m.i.c.), as determined under standardised conditions for the purpose of BS 1259, and both the maximum experimental safe gaps (m.e.s.g.) and the statistical maximum safe gaps (s.m.s.g.), as similarly determined for the purposes of BS 229. The data used were those for the 25 compounds for which determinations both of m.i.c. and m.e.s.g. had been made, covering the whole range, in ease of ignitability, from acetylene to ammonia. It was found that the relations of both m.e.s.g. and s.m.s.g. with log (m.i.c.) were linear over the range, with highly significant correlation coefficients.