Flame Transmission at Extremely Low Temperatures When Pressure Piling Is Present

The International Electrotechnical Commission (IEC) Standard 60079-1 has requirements for testing flameproof enclosures to ensure that there is no transmission of an internal explosion, but there are no special requirements for nontransmission testing for equipment intended for use in extremely low temperatures. The gas mixtures used for test are based on a measure called the maximum experimental safe gap (MESG). It is known that with initial pressures higher than standard atmospheric pressure, flamepaths are less effective and hence the MESG decreases. Conversely, when temperatures are lowered, the flamepaths become more effective and hence the MESG increases. But there is a lack of published literature on how the two effects interact in combination on MESG, in particular at extremely low temperatures. The situation is more complex when pressure piling is present as the pressures become even higher. An analysis of published data suggests that for some gases when the temperature drops from +20 to -60 °C, the impact of pressures may be more significant than the direct impact of temperature on MESG. Hence, transmission may be more likely at lower temperatures where high pressures are present than at ambient temperature. This paper reports on experiments investigating the practical likelihood of flame transmission at extremely low temperatures, in particular when pressure piling is present.