This European Standard 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 atmospheres. The primary purpose of such apparatus is to measure the concentration of a toxic gas or vapour in order to provide an exposure measurement and/or detection and warning of its presence.This European Standard is applicable to apparatus whose primary purpose is to provide an indication, alarm and/or other output function to give a warning of the presence of a toxic gas or vapour in the atmosphere and in some cases to initiate automatic or manual protective actions. It is applicable to apparatus in which the sensor automatically generates an electrical signal when gas is present.This European Standard is not applicable, but may provide useful information, for apparatus—used for the measurement of oxygen,—used only in laboratories for analysis or measurement,— used only for process measurement purposes,—used in car parks or tunnels (fixed apparatus only),—used in the domestic environment,—used in environmental air pollution monitoring,—used for the measurement of combustible gases and vapours related to the risk of explosion.It also does not apply to open-path (line of sight) area monitors.For apparatus used for sensing the presence of multiple gases, this European Standard applies only to the detection of toxic gas or vapour.