BS EN 50402:2005+A1:2008 - Page 2

Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen. Requirements on the functional safety of fixed gas detection systems. | Status: Revised, Superseded, Withdrawn

1 Scope This European Standard is applicable to fixed gas detection systems for the detection and measurement of flammable or toxic1) gases or vapours or oxygen. This European Standard supplements the requirements of the European Standards for electrical apparatus for the detection and measurement of flammable gases, vapours (e.g. EN 61779 or EN 50241), toxic gases (e.g. EN 45544) or oxygen (e.g. EN 50104).

NOTE 1 These European Standards will be mentioned in the text as "metrological standards".

NOTE 2 The examples above show the state of the standardisation for industrial applications at the time of publishing this European Standard. There may be other metrological standards covering other application fields, for which this standard is also applicable.

NOTE 3 For fixed apparatus used for safety applications with a SIL requirement up to 1 and for portable apparatus the European Standard EN 50271 may be applied instead of this European Standard.

Applying the above mentioned metrological standards will ensure the measuring performance is adequate in normal operation of a gas detection system. Additionally the requirements of this European Standard address the functional safety of gas detection systems and encompass criteria for reliability, fault tolerance and avoidance of systematic faults. This European Standard will lead to the characterisation of the gas detection system by a SIL-capability and related hardware failure rate representing a hierarchical order of safety levels. This will allow the user to incorporate the gas detection system into an overall safety system according to the safety integrity levels of EN 61508 or the categories of EN ISO 13849‑1 (see Annex B). This European Standard is a product standard which is based on EN 61508 and includes additional requirements of EN ISO 13849‑1. It covers part of the phase 9 "realisation" of the overall safety lifecycle defined in EN 61508‑1. This European Standard is applicable for gas detection systems, which may consist of the following functional units:

• – gas-sampling;
• – sensor;
• – signal transmission;
• – input to control unit;
• – signal processing in control unit;
• – output from control unit.

This European Standard does not specify requirements for the installation and maintenance of gas detection systems. It also does not specify the physical positioning of sensors.. This European Standard does not specify which SIL-capability is sufficient for which application.

NOTE 4 The SIL-capability required for an application will be specified by the user (see Annexes A and B).