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.

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What IEC 60079, Explosive Atmospheres, Hazardous Area Equipment means.

IEC 60079 is structured as a series of parts. Part 0 covers general requirements. Parts 1, 7, 11, 15, 18, 26 cover specific protection methods. Part 10 covers area classification. Part 14 covers electrical installation in hazardous areas. Part 17 covers inspection and maintenance. Operating companies and EPC contractors typically reference Part 10, area classification report, Part 14, installation, and Part 17, maintenance and inspection as the lifecycle anchor for hazardous-area electrical work. The North American Class, Division, Group system, NEC Article 500 is technically equivalent at the design level but uses different terminology. NEC Article 505 adopts the IEC zone system for new installations.

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.

Worked example, decoding an equipment marking.

A transmitter nameplate reads II 2 G Ex db ia IIC T4 Gb. Read it field by field. II is the equipment group, meaning surface industry rather than mining. 2 is the ATEX equipment category, which corresponds to Zone 1 for gas. G says the atmosphere is gas rather than dust. Ex introduces the protection concepts, and there are two here: db is flameproof enclosure at level of protection b, and ia is intrinsic safety at level a, so part of the device is inside a flameproof housing and part of the circuit is intrinsically safe. IIC is the gas group, the most demanding of the surface groups, covering hydrogen and acetylene, and equipment marked IIC is also suitable where IIB or IIA is required. T4 is the temperature class, so the maximum surface temperature stays below 135 degrees C. Gb is the equipment protection level, which corresponds to Zone 1. The check that matters is the last one: compare Gb against the zone the hazardous area drawing gives for that location. Gb suits Zone 1 and Zone 2, and does not suit Zone 0.

IEC 60079 zone classification and equipment protection level

Zones are defined by how often an explosive atmosphere is present. IEC 60079-10-1 classifies gas, IEC 60079-10-2 classifies dust. The ATEX category column is the European equipment category that matches each zone.

Zone	Atmosphere	Presence of an explosive atmosphere	Equipment protection level	ATEX category
Zone 0	Gas, vapour or mist	Present continuously, or for long periods, or frequently	Ga	1G
Zone 1	Gas, vapour or mist	Likely to occur in normal operation, occasionally	Gb	2G
Zone 2	Gas, vapour or mist	Not likely in normal operation, and only for a short period if it does	Gc	3G
Zone 20	Combustible dust	Present continuously, or for long periods, or frequently	Da	1D
Zone 21	Combustible dust	Likely to occur in normal operation, occasionally	Db	2D
Zone 22	Combustible dust	Not likely in normal operation, and only for a short period if it does	Dc	3D

Protection concepts, the Ex letter codes

Each concept is a different way of keeping an ignition source and an explosive atmosphere apart. The letter appears in the equipment marking and in the hazardous area schedule.

Code	Concept	How it works	Standard part	Zones it suits
Ex d	Flameproof enclosure	Contains an internal explosion and cools the escaping gas below the ignition temperature	IEC 60079-1	1 and 2
Ex e	Increased safety	No arcs, sparks or hot surfaces in normal operation, with extra construction margin	IEC 60079-7	1 and 2
Ex ia, ib, ic	Intrinsic safety	Limits the energy in the circuit below what can ignite the atmosphere	IEC 60079-11	ia in 0, ib in 1, ic in 2
Ex p	Pressurisation	Keeps the atmosphere out of the enclosure with a protective gas at positive pressure	IEC 60079-2	1 and 2
Ex ma, mb, mc	Encapsulation	Embeds the ignition source in a compound so no atmosphere can reach it	IEC 60079-18	ma in 0, mb in 1, mc in 2
Ex o	Oil immersion	Submerges the ignition source in a protective liquid	IEC 60079-6	1 and 2
Ex q	Powder filling	Surrounds the ignition source with a fine granular filling	IEC 60079-5	1 and 2
Ex ec	Increased safety, level of protection c	No ignition source in normal operation; replaced the older Ex nA	IEC 60079-7	2 only
Ex t	Protection by enclosure, dust	A dust tight or dust protected enclosure with a limited surface temperature	IEC 60079-31	20, 21 and 22
Ex op is, pr, sh	Optical radiation	Limits or contains optical energy that could act as an ignition source	IEC 60079-28	By the level declared

Gas groups and temperature classes

The gas group says how easily the atmosphere ignites; the temperature class says how hot the equipment surface is allowed to get. Equipment is suitable only if it meets or exceeds both.

Marking	Meaning	Representative gas or limit
Group I	Mining, methane, and coal dust	Underground coal mining equipment
Group II	Surface industry, gas and vapour	Subdivided into IIA, IIB and IIC
IIA	The least easily ignited of the surface groups	Propane
IIB	Intermediate	Ethylene
IIC	The most easily ignited; equipment marked IIC also covers IIB and IIA	Hydrogen and acetylene
Group III	Surface industry, dust	IIIA combustible flyings, IIIB non-conductive dust, IIIC conductive dust
T1	Maximum surface temperature 450 degrees C	Covers T1 only
T2	Maximum surface temperature 300 degrees C	Covers T1 and T2
T3	Maximum surface temperature 200 degrees C	Covers T1 to T3
T4	Maximum surface temperature 135 degrees C	Covers T1 to T4; the most common requirement in process plant
T5	Maximum surface temperature 100 degrees C	Covers T1 to T5
T6	Maximum surface temperature 85 degrees C	Covers T1 to T6; the most demanding

Common questions

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 plus 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.

Written byTagsight Functional Safety DeskUpdated 20 September 2026

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