ATEX Ratings, Intrinsic Safety, Hazardous Areas and Explosive Atmospheres

Please note that this page provides helpful information only, detailed reference should be taken from an appropriate accredited agency or organisation.

Protection Concepts
Zone Hazard Protection Concepts
0 In which an explosive gas/air mixture is continuously present for long periods Exia or Exs
1 In which an explosive gas/air mixture is likely to occur in normal operation. Exd. Exe, Exib, Exp, Exia, Exs
2 In which an explosive gas/air mixture is not likely to occur in normal operation. All concepts suitable for Zone 0 & 1, ExN, ExO and Exq


Standards For Methods Of Protection
Method Of Protection Permitted Zone Of Use In UK Code Letter IEC, EX.., CENELEC, EEX
General requirement
Oil immersion 2 o
Pressurisation 1 or 2 p
Powder filling 2 q
Flameproof 1 or 2 d
Increased safety 1 or 2 e
Intrinsic safety * 0, 1 or 2 ia or ib
Non-incendive 2 n #
Encapsulation 1 or 2 m
Special 1 or 2 s
* ia: Zone 0, 1, 2  /   ib: Zone 1 or 2 but not Zone 0  |  # n: used locally in UK
Gas Grouping Temperature Classification
Gas # Group CENELEC EN 5014, IEC Representative Gas T Class /
IEC 79-7
Max. Surface Temp °C
I * (mining) Methane T1 450°C
IIA Propane T2 300°C
IIB Ethylene T3 200°C
IIC Hydrogen T4 135°C
T5 100°C
T6 85°C


Certification Code (CENELEC marking information – example [EEx ia] IIC T4)
[ E Ex ia ] IIC T4
Associated apparatus* Certified to the CENELEC standard Explosion protected Protection concept (IS) Associated apparatus* Apparatus group (gas group) Temperature classification (not Gp I)
* (located in safe area and may be connected to hazardous area)


Device Group & Category
Device Group Device Category Zone
I M = Mining
Mining M 1
Pit Gas &/or Flammable Dusts M 2
II G = Gas
Other areas 1 G 0, 1, 2
Explosive Atmosphere 2 G 1, 2
3 G 2
D is added after G in the certification class number D = Dust
(i.e. GD) if device is dust category approved also 1 D 20, 21, 22
2 D 21, 22
3 D 22
Explanation of the categories:
1 – Very high safety = device safety must be guaranteed even in case of rare device failures, e.g. simultaneous failure of two components.2 – High safety = device safety must be guaranteed if frequent failures can be expected, e.g. failure of one component.3 – Safe in normal operation = device safety must be guaranteed in normal operation.Note: A number in brackets before device category designation signifies that the device meets the requirements of an additional category to the main one that is specified.

Example: II (1) 2G signifies that the device meets requirements for both 1 G and 2 G categories

Characteristics of Substances


This is the lowest temperature at which a liquid generates sufficient vapour to support ignition. This vapour can be ignited in many ways including temperature or energy (i.e. a spark)

Ignition Temperature

This is the lowest temperature at which the vapour will be ignited.  This defines the temperature class.

Classification of maximum surface temperatures of electrical apparatus (CENELEC)
Temp. Class Max. Surface Temp.
T1 <450ºC
T2 <300ºC
T3 <200ºC
T4 <135ºC
T5 <100ºC
T6 <85ºC

Apparatus Group (Energy Ignition)

All surface industry gases/vapours are classed as Group II gases.  Group II is divided into 3 sub groups:

IIA – High energy is required to ignite. Less intense explosion. (Propane)

IIB – Less energy is required to ignite.  More intense explosion. (Ethylene)

IIC – Little energy is required to ignite. Most intense explosion. (Hydrogen)

Characteristics Of Some Common Flammable Materials
Gas/Vapour Flashpoint Gas Group Ignition Temp. Temp. Class
Acetone 19ºC IIA 535ºC T1
Butane -60ºC IIA 365ºC T2
Heptane -4C IIA 215ºC T3
Ethyl Methyl Ether 37ºC IIB 190ºC T4

Note: There is no connection between ignition energy and ignition temperature

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