# IEC 60079-0 — Equipment General Requirements for Explosive Atmospheres

> 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.

- Source : https://industryhub.site/en/standards/iec-60079-0
- Body : IEC
- Family : Hazardous Areas
- Status : current
- First published : 1971 (early editions of IEC 79-0)
- Latest revision : 2017 (Edition 7) + Amendment 1:2021
- Edition : 7
- Next revision : Edition 8 in committee draft
- Access : Paid (IEC webstore — ~250 CHF)
- Language : English

## Document structure

- **IEC 60079-0:2017+A1:2021** — Equipment — General requirements : 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.

## Key concepts

- **Equipment Group** : Group I = mining equipment (firedamp methane). Group II = surface industries (gas atmospheres). Group III = dust atmospheres. Different categories within each group correspond to acceptable zones (per ATEX) or EPL (per IECEx).
- **Gas Group classification** : Group IIA (e.g., propane, butane, easiest to protect against). Group IIB (ethylene, methylene). Group IIC (hydrogen, acetylene — hardest, smallest minimum ignition energy). An Ex device certified IIC is automatically suitable for IIA and IIB. Reverse is NOT true.
- **Dust Group classification** : Group IIIA (combustible flyings, e.g., textile fibers). Group IIIB (non-conductive dust, e.g., flour). Group IIIC (conductive dust, e.g., aluminum, magnesium — most dangerous because of conductivity bridging and lower ignition energies).
- **Temperature Class (T-class)** : Maximum surface temperature an Ex device can reach during normal AND specified fault conditions. T1=450°C, T2=300°C, T3=200°C, T4=135°C, T5=100°C, T6=85°C. Must remain below the surrounding gas/dust auto-ignition temperature with safety margin.
- **Equipment Protection Level (EPL)** : Ga/Gb/Gc for gas (Very High / High / Enhanced protection). Da/Db/Dc for dust. Ma/Mb for mining. EPL maps to ATEX Category : Ga ≈ Cat 1G, Gb ≈ Cat 2G, Gc ≈ Cat 3G.
- **Marking format** : Per clause 29. Standard layout: '|II 2(1) G Ex eb [ia] IIC T4 Gb (Ga)' decoded as : Group II surface, Category 2 with Cat 1 internal part, Gas atmosphere, Ex protection methods (eb increased safety + [ia] intrinsic safety inside), Gas group IIC, T4 (135°C), EPL Gb with internal Ga part.
- **Ambient temperature range** : Standard certification = -20°C to +40°C. Marking with 'Ta' indicates extended range, e.g., 'Ta -40°C to +60°C'. Outside this range, certification doesn't apply.

## Why IEC 60079-0 is the rosetta stone

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 60079
- `ia` — 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°C
- `Ga` — 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.

## The Equipment Group / Category / EPL triangle

| 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**.

## Gas groups — minimum ignition energy

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.

## Temperature class vs. gas Auto-Ignition Temperature

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).

## What's new in 2017 / 2021 amendment

Compared to Edition 6 (2011), Edition 7 brought :
- Clarification of marking requirements (especially compound markings like 'Ex eb [ia]')
- Updated material requirements (plastics ESD, light metals fire risk)
- Tightened cable entry requirements (avoid Ex e gland on Ex d enclosure mis-pairing)
- More precise dust marking requirements

Amendment 1:2021 added :
- More guidance on "Special Protection" (Ex s) method
- IECEx 'OD' (Operational Document) references
- Better integration with hydrogen-specific requirements

The committee is preparing Edition 8 with focus on :
- Battery storage in Ex (large lithium installations)
- Wireless communication safety (5G, BLE in Ex)
- Cybersecurity touch points (IEC 62443 mention in Ex context)
- Updated definitions for new combustion chemistries (alternative fuels, ammonia, H2)

## What this means for engineering

When specifying Ex equipment, your **marking specification** in the datasheet must include :
- Equipment Group (I, II G, II D, depending on environment)
- Category / EPL
- Protection method(s) acceptable for your application
- Gas group (must cover all gases present)
- T-class (must respect AIT of all gases present)
- Ambient temperature range (-20/+40 standard, extend if needed)

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."

## Applicable industries

All hazardous area industries (Oil & Gas, Chemical, Pharma, Mining, Pulp & Paper), Food and beverage (dust), Metal processing (combustible dust), Pharmaceutical (solvents, dust), Underground mining (Group I)

## References & further reading

- [IEC 60079-0:2017+A1:2021 — official](https://webstore.iec.ch/publication/32878)
- [PTB — Ex marking explainer](https://www.ptb.de/cms/en/ptb/fachabteilungen/abt3/dept-37.html)