This European Standard specifies the performance requirements for electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours in workplace atmospheres. The standard test gas concentration (STGC) to be used for the tests are given in annex A of prEN 45544-1. In the instances in which no STGC is assigned in 5.6 of prEN 45544-1:1998, a STGC may be agreed between the manufacturer and test laboratory considering the National limit values.