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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 |
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 |
Flashpoint
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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