This European Standard gives guidelines for background information and gives guidance on the selection, installation, use and maintenance of electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours in workplace air. It is concerned with apparatus whose primary purpose is to indicate the presence and concentration of a toxic gas or vapour to provide a rapid indication or warning of the presence of a toxic hazard within a time of response as specified in accordance with EN 45544-2 and EN 45544-3.