IEC 61779-4 Ed. 1.0 en:1998

Specifies requirements for group II (as defined in part 1) portable, transportable and fixed apparatus for the detectino and measurement of combustible gas or vapour concentrations with air. The apparatus, or parts thereof, may be installed or used in potentially explosive atmospheres, other than mines susceptible to firedamp (i.e. group I). This standard is restricted to apparatus intended for the detection and measurement of combustible gas or vapour concentrations with air up to 100% lower explosive limit (LEL).