EN/IEC 60079-0 specifies the basic requirements for electrical equipment intended for use in explosive atmospheres at standard atmospheric conditions and the ‘normal’ ambient temperature range for Ex equipment is generally given at as –20 °C to +40 °C unless marked otherwise.

It is considered that –20 °C to +40 °C is appropriate for many items of Ex Equipment and that to manufacture all Ex Equipment to be suitable for a standard atmosphere upper ambient temperature of +60 °C would place unnecessary design constraints.