Lowest temperature of a heated surface at which, under specified conditions, the ignition of a flammable substance in the form of a gas or vapour mixture with air will occur. [IEV 426-02-01, modified]
NOTE IEC 60079-4 and IEC 60079-4A standardize a method for the determination of this temperature.
Source: IEC 61892-7, Mobile and fixed offshore units – Electrical installations – Part 7: Hazardous areas. Global Standards