Definition(s)
Explosive Gas Atmosphere (Gas Properties)
Mixture with air, under normal atmospheric conditions, of flammable substances in the form of gas or vapour, in which, after ignition, self-sustaining flame propagation.
NOTE 1 This definition specifically excludes dusts and fibres in suspension in air. Mists are not covered by this standard.
NOTE 2 Although a mixture that has a concentration above the upper flammable limit (see 3.1.9) is not an explosive atmosphere, in certain cases for area classification purposes, it is advisable to consider it as an explosive gas atmosphere.
NOTE 3 Normal atmospheric conditions include variations above and below the reference levels of 101,3 kPa and 20 °C provided the variations have a negligible effect on the explosive properties of the flammable materials.
Source: IEC 60079-29-1, Explosive atmospheres – Part 29-1: Gas detectors – Performance requirements of detectors for flammable gases. Global Standards
Explosive Gas Atmosphere
Mixture with air, under atmospheric conditions, of flammable substances in the form of gas or vapour in which, after ignition, combustion spreads throughout the unconsumed mixture [IEV 426-02-03, modified].
NOTE Although a mixture which has a concentration above the upper explosive limit (UEL) is not an explosive gas atmosphere, it can readily become so and, in certain cases for area classification purposes, it is advisable to consider it as an explosive gas atmosphere.
Source: IEC 61892-7, Mobile and fixed offshore units – Electrical installations – Part 7: Hazardous areas. Global Standards