IEC 60079-0 is the foundation of the IEC 60079 series. It defines the general requirements applicable to all Ex equipment — markings, temperature classes, gas groups, dust groups, Equipment Protection Levels (EPL), construction principles. Every other IEC 60079 protection-method part references this one.
IEC 60079-0:2017+A1:2021 Single document. ~30 clauses covering scope, equipment groupings (I mining vs II surface vs III dust), temperature classes, gas/dust groups, EPL classification, materials and construction (enclosures, fasteners, cable entries, transparent parts), marking format and content, documentation, type tests.
(T-class) (EPL) Every Ex device sold worldwide carries a marking that follows a specific format defined by IEC 60079-0 clause 29. Learn to read it, and you can grade compliance of any device in 30 seconds without opening the certificate.
A typical level transmitter for petrochemical service:
|II 2 G Ex ia IIC T4 Ga
Decoded:
|II — Equipment Group II (surface industries, not mining)2 — Category 2 (suitable for Zone 1 with EPL Gb at minimum)G — Gas atmosphere (not dust)Ex — meets one of the explosion protection methods defined by IEC 60079ia — protection method “intrinsic safety, fault tolerance 2” (per IEC 60079-11)IIC — gas group : safe with hydrogen and acetylene (the hardest)T4 — surface temperature max 135°CGa — EPL Ga = highest protection (suitable for Zone 0)So this device, despite being labeled “Category 2”, actually achieves EPL Ga and can be used in Zone 0 (continuous explosive atmosphere). The mismatch between ATEX category (2) and IECEx EPL (Ga) is allowed when the marking explicitly states the higher EPL.
| ATEX Group | Industry | Cat 1 | Cat 2 | Cat 3 |
|---|---|---|---|---|
| Group I | Mining (methane) | EPL Ma | EPL Mb | (none) |
| Group II G | Gas surface | EPL Ga (Zone 0) | EPL Gb (Zone 1) | EPL Gc (Zone 2) |
| Group II D | Dust | EPL Da (Zone 20) | EPL Db (Zone 21) | EPL Dc (Zone 22) |
The ATEX Directive 2014/34/EU uses Categories. IECEx and IEC 60079-0 use EPLs. They map 1-to-1 within each group.
The MIE (Minimum Ignition Energy) for various gases (in mJ) :
| Gas | MIE | IEC Group |
|---|---|---|
| Methane | 0.28 | IIA |
| Propane, Butane | 0.25 | IIA |
| Ethylene | 0.07 | IIB |
| Hydrogen | 0.016 | IIC |
| Acetylene | 0.017 | IIC |
The lower the MIE, the easier the gas ignites, the more rigorous the protection requirements. Hydrogen at 16 µJ is the hardest case — even tiny electrostatic discharges from a static-charged worker can ignite it. This is why hydrogen-handling installations are universally Group IIC.
The growing hydrogen economy (electrolysers, fuel cells, H2 storage) is driving renewed attention to Group IIC certification because everything that worked for natural gas (Group IIA) may not be adequate for H2.
The T-class must be lower than the AIT of every gas present, with margin :
| Gas | AIT (°C) | Minimum T-class |
|---|---|---|
| Diesel vapor | 210 | T3 (200°C) |
| Methane | 595 | T1 (450°C) |
| Hydrogen | 560 | T1 (450°C) |
| Acetylene | 305 | T2 (300°C) |
| Carbon disulfide | 90 | T6 (85°C) — extreme case |
| Hexane | 225 | T3 (200°C) |
For multi-gas environments, take the lowest AIT in the mix as the binding constraint. A refinery with diesel + crude oil vapors typically needs T3 minimum (sometimes T4 for safety margin).
Compared to Edition 6 (2011), Edition 7 brought :
Amendment 1:2021 added :
The committee is preparing Edition 8 with focus on :
When specifying Ex equipment, your marking specification in the datasheet must include :
Example for a refinery instrument tag in Zone 1 with hydrogen presence:
“Equipment shall be ATEX Category 2G, EPL Gb minimum, gas group IIC (or device-specific equivalent covering H2), temperature class T3 minimum, ambient -20°C to +60°C, with marking compliant to IEC 60079-0 clause 29.”