This European Standard specifies minimum requirements and tests for electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen using software and/or digital technologies. This European Standard is applicable to fixed, transportable and portable apparatus intended for use in domestic premises as well as commercial and industrial applications and their software-controlled safety related accessories. This European Standard does not apply to external sampling systems which are not accessories, or to apparatus of laboratory or scientific type, or to apparatus used only for process control purposes. This European Standard supplements the requirements of the European Standards for the detection and measurement of flammable gases and vapours (e.g. EN60079‑29‑1 , EN60079‑29‑4 , EN50194‑1 , EN50194‑2 ), toxic gases (e.g. EN45544 series, EN50291‑1 , EN50291‑2 ) or oxygen (e.g. EN50104 ). NOTE1 These European Standards will be mentioned in this European Standard as “metrological standards”. NOTE2 The examples above show the state of the standardization for gas detection apparatus at the time of publishing this European Standard. There may be other metrological standards for which this European Standard is also applicable. This European Standard is a product standard which is based on the EN61508 series. It covers part of the phase 10 “realisation” of the overall safety life cycle defined in EN61508‑1 . Additional requirements are specified if compliance with safety integrity level 1 (SIL 1) according to the EN61508 series is claimed for fixed or transportable apparatus for low demand mode of operation. They can also be applied to portable apparatus which are able to perform an automatic executive action. It is recommended to apply this European Standard for apparatus used for safety applications with SIL-requirement 1 instead of EN50402 . However, the technical requirements of EN50271 and EN50402 are the same for SIL 1. NOTE3 For apparatus used for safety applications with SIL-requirements higher than 1 EN50402 is applicable.