1.1 This part of 61779 specifies requirements for group II (as defined in part 1) portable, transportable and fixed apparatus for the detection 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). The requirements and test methods applicable to the apparatus covered by this standard are specified in part 1. 1.2 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).