hazardIEC 60079-0 specifies the general requirements for construction, testing and marking of electrical apparatus and Ex components intended for use in explosive gas atmospheres.

Unless modified by one of the parts in the IEC 60079 series, electrical apparatus complying with this standard is intended for use in hazardous areas in which explosive gas atmospheres, caused by mixtures of air and gases, vapours or mists, exist under normal atmospheric conditions of

  • temperature –20 °C to +60 °C;
  • pressure 80 kPa (0,8 bar) to 110 kPa (1,1 bar); and
  • air with normal oxygen content, typically 21 % v/v.

The application of electrical apparatus in atmospheric conditions outside this range may need special consideration.

NOTES

  1. The determination of the maximum surface temperature is based on an operational ambient temperature of –20 °C to +40 °C, if not otherwise specified by the manufacturer.
  2. n designing apparatus for operation in explosive gas atmospheres under conditions other than the atmospheric conditions given above, this standard may be used as a guide. However, additional testing related specifically to the intended conditions of use is recommended. This is particularly important when the types of protection 'flameproof enclosures "d"' (IEC 60079-1) and 'intrinsic safety "i"' (IEC 60079-11) are applied. 
  3. equirements given in this standard result from an ignition hazard assessment made on electrical equipment. The ignition sources taken into account are those found associated with this type of equipment, such as hot surfaces, mechanically generated sparks, thermite reactions, electrical arcing and static electric discharge in normal industrial environments. For other ignition sources like adiabatic compression, shock waves, exothermic chemical reaction, self ignition of dust, naked flames, hot gases/liquids the apparatus are subjected to a hazard analysis that identifies and lists all of the potential sources of ignition by the electrical apparatus and the measures to be applied to prevent them becoming effective.

 


This standard does not specify requirements for safety, other than those directly related to the explosion risk.
This standard is supplemented or modified by the following parts of IEC 60079 concerning specific types of protection:

  • IEC 60079-1: Flameproof enclosures "d";
  • IEC 60079-2: Pressurized enclosures "p";
  • IEC 60079-5: Powder filling "q";
  • IEC 60079-6: Oil immersion "o";
  • IEC 60079-7: Increased safety "e";
  • IEC 60079-11: Intrinsic safety "i";
  • IEC 60079-15: Type of protection "n";
  • IEC 60079-18: Encapsulation "m".


Apparatus grouping and temperature classification
Electrical apparatus for explosive gas atmospheres is divided into the following:

  • Group I: electrical apparatus for mines susceptible to firedamp; 
  • roup II: electrical apparatus for places with an explosive gas atmosphere other than mines susceptible to firedamp.


Electrical apparatus intended for mines where the atmosphere, in addition to firedamp, may contain significant proportions of other flammable gases (i.e. other than methane), shall be constructed and tested in accordance with the requirements relating to Group I and also to the subdivision of Group II corresponding to the other significant flammable gases. This electrical apparatus shall then be marked appropriately (for example, "Ex d I/IIB T3" or "Ex d I/II (NH3)").

Temperatures

Electrical apparatus shall normally be designed for use in an ambient temperature range between –20 °C and +40 °C; in this case, no additional ambient temperature marking is necessary.
Electrical apparatus designed for use in a different range of ambient temperatures is considered to be special, and the ambient temperature range shall then be stated by the manufacturer. The marking shall then include either the symbol Ta or Tamb together with the special range of ambient temperatures or, if this is impracticable, the symbol "X" shall be used to indicate special conditions of use that include a special range of ambient temperature.

Maximum surface temperature shall be determined for rated duty of the electrical apparatus but with the voltage between 90 % to 110 % of the rated voltage or the specific requirement of the standard for the type of protection, and when the apparatus is subjected to maximum ambient temperature and, where relevant, the maximum rated external source of heating.

For electrical apparatus of Group I, the maximum surface temperature shall be specified according to the manufacturer's documentations that give a full and correct specification of the explosion safety aspects of the electrical apparatus.

This maximum surface temperature shall not exceed

  • 150 °C on any surface where coal dust can form a layer,
  • 450 °C where coal dust is not expected to form a layer (for example, due to sealing or ventilation), provided that the actual maximum surface temperature is marked on the apparatus.

Classification of maximum surface temperatures for Group II electrical apparatus

Temperature class     Maximum surface temperature
        T1                                     450°C
        T2                                     300°C
        T3                                     200°C
        T4                                     135°C
        T5                                     100°C
        T6                                     85°C

More than one temperature class may be established for different ambient temperatures and different external sources of heating and cooling.