IEC 60079 (Explosive Atmospheres / Hazardous Area Equipment)
IEC 60079 is the international standard series governing electrical equipment for use in explosive atmospheres (Ex equipment). The standard defines hazardous area zone classification (Zone 0, Zone 1, Zone 2 for gas; Zone 20, Zone 21, Zone 22 for dust), the protection methods for electrical equipment (flameproof Ex d, intrinsically safe Ex i, increased safety Ex e, pressurized Ex p, encapsulation Ex m, oil immersion Ex o, powder filling Ex q, type of protection n Ex n, special Ex s), and the marking convention that identifies the protection method, zone, and gas group. The North American equivalent is NEC Class / Division / Group classification.
How does the IEC zone classification work?.
Zone 0 is an area where an explosive gas atmosphere is present continuously or for long periods; equipment must be intrinsically safe Ex ia or specially certified. Zone 1 is an area where an explosive gas atmosphere is likely to occur in normal operation; equipment in Ex d, Ex e, Ex ib, Ex p, Ex m, Ex o, Ex q is acceptable. Zone 2 is an area where an explosive gas atmosphere is not likely to occur in normal operation and, if it does, will exist only for a short period; Ex n equipment plus all higher zone categories are acceptable. The dust zones (20, 21, 22) parallel the gas zones for combustible dust environments.
What do the gas groups (IIA, IIB, IIC) mean?.
Gas group IIA covers propane-class gases (least restrictive); IIB covers ethylene-class gases (more restrictive); IIC covers hydrogen and acetylene (most restrictive). Each higher group requires tighter flame-path gaps in Ex d equipment, lower maximum surface temperatures, and more restrictive intrinsic-safety energy limits. Equipment certified for IIC is acceptable in IIA and IIB areas; equipment certified for IIA only is not acceptable in IIB or IIC areas. The gas group of the area drives equipment selection.
What is the marking convention?.
Ex equipment carries a marking like Ex db IIC T4 Gb. 'Ex' identifies the equipment as explosion-protected; 'd' identifies the protection method (flameproof); the lowercase letter after 'd' identifies the equipment protection level (a, b, c - corresponding to Zone 0, 1, 2 suitability); 'IIC' identifies the gas group; 'T4' identifies the temperature class (maximum surface temperature 135°C); 'Gb' identifies the equipment protection level for gas (a is highest, c is lowest). Equivalent dust marking uses 't' for type of protection 't' (enclosure), 'IIIA/B/C' for dust groups, 'T' followed by Celsius temperature, and 'Da/Db/Dc' for dust EPL.
Frequently asked.
What is the difference between IEC zones and NEC Class/Division?
IEC uses Zones 0, 1, 2 for gases and Zones 20, 21, 22 for dust. NEC Class I (gas) Division 1 (similar to IEC Zone 0 + Zone 1) and Division 2 (similar to Zone 2); NEC Class II (dust) Division 1 and 2. The IEC system is more granular (separating continuous Zone 0 from intermittent Zone 1); NEC Article 505 allows the IEC zone system as an alternative in the U.S. for new installations.
What is intrinsic safety (Ex i)?
Intrinsic safety is a protection method that limits the electrical energy in field circuits below the level required to ignite the explosive atmosphere. Intrinsically safe circuits can be installed in Zone 0; energy limits are controlled by an intrinsic-safety barrier or galvanic isolator at the safe-area boundary. The method is preferred for field instrumentation (transmitters, switches, RTDs) because it allows live maintenance work in the hazardous area.
What is ATEX vs. IECEx?
ATEX is the EU directive (2014/34/EU) governing the marketing of equipment for explosive atmospheres in the EU. IECEx is the international certification scheme operated by IEC. Equipment certified to IECEx is generally accepted under ATEX with additional administrative steps. ATEX uses the EPL marking (Ga, Gb, Gc for gas; Da, Db, Dc for dust); IECEx uses the same EPL marking system.
Does IEC 60079 apply to mechanical equipment?
IEC 60079 covers electrical equipment. Mechanical equipment for hazardous areas (rotating equipment, fans, compressors) is governed by ISO 80079 (Non-electrical equipment for explosive atmospheres). Mechanical equipment in hazardous areas must also be certified; the zone classification and gas group apply the same way.