BS EN 50495:2010 - Page 2

Safety devices required for the safe functioning of equipment with respect to explosion risks. | Status: Confirmed, Current

1 Scope This European Standard specifies the requirements of electrical safety devices, which are used to avoid potential ignition sources of equipment in explosive atmospheres. This also includes safety devices, which are operated outside areas with explosive atmospheres, to guarantee the safe function of equipment with respect to explosion hazards.

NOTE 1 This European Standard can also be used to design and assess safety devices for protective systems.

Electrical equipment, which is intended for use in explosive atmospheres, may rely on the correct operation of safety devices which for example maintain certain characteristics of the equipment within acceptable limits. Examples of such safety devices are motor protection devices (to limit temperature rise during stall conditions) and controlling devices for pressurisation protection. By means of control or monitoring devices, sources of ignition can be avoided. Therefore these devices shall execute the appropriate measures in the appropriate reaction time, for example the initiation of an alarm or an automatic shut down.

NOTE 2 Some potential ignition sources might not be controllable by safety devices, e.g. electrostatic discharges, ignition sparks caused by mechanical impact. Also some protection measures might not be controllable by safety devices, e.g. flameproof enclosures.

Safety devices, whose safety function can not adequately be specified under the existing EN 60079 or EN 61241 series of standards, shall additionally be designed according to the requirements of this standard. Generally for complex safety devices appropriate design requirements are not provided in the existing types of protection (see 3.13 for the definition of a complex device).

NOTE 3 In general the levels of safety required by this standard are considered to be equivalent to those provided by conformity to EN 60079‑0 or EN 61241‑0. No increase or decrease of safety is intended or required. Similarly neither increase nor decrease of safety with respect to EN 61508 series is intended.

Safety devices can be classified in 2 types:

1. a) devices, which are included as component in the equipment under control (see 3.8). The combined apparatus is considered as equipment. EXAMPLES
   • – thermal switch or thermistor to avoid overheating,
   • – temperature monitoring devices to control the surface temperature.
2. b) devices, which are installed separately from the equipment under control and considered as associated apparatus exclusively for a specific type of protection or specific equipment under control. The combined apparatus is considered as a system. EXAMPLES
   • – external control devices or safety related parts of a control system for type of protection pressurisation,
   • – overload protective device for electric motors of type of protection Ex e ‘Increased Safety’,
   • – control devices for battery charging equipment (protection against overcharging or deep discharging),
   • – level detectors for the control of submersible pumps.

Exclusions from this standard: Safety devices, where the safety function is adequately covered in the existing standards of EN 60079 and EN 61241 series do not need any additional assessment according to this standard. EXAMPLES Intrinsically safe associated apparatus, fuses, electromechanical overload protection, simple thermal protection devices (e.g. thermal fuses, thermal switches). The standard does not include devices or systems to prevent the occurrence of explosive atmospheres, e.g. inerting systems, ventilation in workplaces and containers/vessels. Gas detectors, which are covered under EN 61779 series, EN 50271 or EN 50402 are also excluded from the scope of this standard. This standard does not deal with protection by control of ignition source ‘b’ for non-electrical equipment as defined in EN 13463‑6.