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. Additional requirements are specified if compliance with safety integrity level 1 (SIL 1) according to EN 61508 series is required for low demand mode of operation.NOTE 1 It is recommended to apply this European Standard for apparatus used for safety applications with SIL-requirement 1 instead of EN 50402. However, the technical requirements of EN 50271 and EN 50402 are the same for SIL 1.NOTE 2 For fixed apparatus used for safety applications with SIL-requirements higher than 1 EN 50402 is applicable.This European Standard is applicable to fixed, transportable and portable apparatus intended for use in domestic premises as well as commercial and industrial applications.This European Standard does not apply to external sampling systems, 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. EN 60079 29 1, EN 50241 1, EN 50241 2, EN 50194 1, EN 50194 2), toxic gases (e.g. EN 45544 series, EN 50291 1, EN 50291 2) or oxygen (e.g. EN 50104).NOTE 3 These European Standards will be mentioned in this European Standard as "metrological standards".NOTE 4 The examples above show the state of the standardisation 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 EN 61508 series. It covers part of the phase 9 "realisation" of the overall safety life cycle defined in EN 61508 1.