Standards for potentially explosive areas (ATEX)
Definition of ignition protection category
EN 50015: Ignition protection category: oil immersion »o«
EN 50016: Ignition protection category: pressurised enclosure »p«
EN 50017: Ignition protection category: powder filling »q«
EN 50018: Ignition protection category: flameproof enclosure »d«
EN 50019: Ignition protection category: increased safety »e«
EN 50020: Ignition protection category: intrinsic safety »i«
EN 50028: Ignition protection category: encapsulation »m«
EX-marking
Units that meet all the requirements of the directive 94/9/EC may carry the CE
mark. As this mark is also used for non-explosion protected products, the familiar
hexagonal Ex is retained as a distinguishing mark when relevant EU directives
control free movement for these products across the Community's internal
borders.
As well as the equipment group (I or II), the category must also be stated and, for
group II, the letter G or D. Letter markings may be combined, for example
..II..G/D, where devices are equally suitable for use in potentially explosive
atmospheres arising from gases or dust.
Selecting the right electrical equipment
In order to select the right electrical equipment it's necessary to know the
classification of the flammable mixtures that may be present in these explosion
groups. The ignitability and likelihood of flashover of a potentially explosive
mixture are properties that are specific to the substance. The requirements for
electrical equipment can therefore be graduated depending on the gases or
vapours present within the application area.
Temperature classes
The ignition temperature depends on the substance. It is defined as the lowest
temperature at which the gas will still ignite, established as part of a test
arrangement.
Based on the different ignition temperatures established on various gases, the
flammable gases and vapours are classified into temperature classes. For all
ignition protection categories it is necessary to classify the electrical equipment
to be installed in the potentially explosive area into temperature classes T1 to T6.
Temperature class Max surface temp Ignition temp of flammable substance
T1
450
>450
T2
300
> 300
T3
200
>200
T4
135
>135
T5
100
>100
T6
85
>85
Prevention of ignition sources within the explosion protection area
Ignition sources, whether as part of the operation or as a result of a fault, must be
avoided in the explosion protection area. The device manufacturer must know
how the ignition protection category can be used to achieve this objective on the
individual equipment.
Definition of ignition protection category
Ignition protection categories are measures that are taken on electrical
equipment to prevent that equipment from igniting an external explosive
atmosphere.
EN 50015: Ignition protection category: oil immersion »o«
Type of protection where electrical equipment or parts of the electrical
equipment are immersed in oil in such a way that an explosive atmosphere that
may be above the liquid or outside the housing cannot be ignited.
EN 50016: Ignition protection category: pressurised enclosure »p«
Type of protection where the ingress of the external atmosphere into the
electrical equipment housing is prevented by maintaining a protective gas (air,
inert or other appropriate gas) internally at a pressure above that of the external
atmosphere. The overpressure is maintained with or without purging of the
protective gas.
EN 50017: Ignition protection category: powder filling »q«
Type of protection where the housing of the electrical equipment is filled with a
mass of granular material so that, if an arc occurs within the housing under
normal usage, that arc will not ignite an external explosive atmosphere. Ignition
must not be possible, whether as the result of flames or increased temperatures
on the housing surface.
EN 50018: Ignition protection category: flameproof enclosure »d«
Type of protection where the parts that could ignite a potentially explosive
atmosphere are contained within an enclosure, which will withstand an internal
explosion of a flammable mixture, without communicating the internal explosion
to the external explosive atmosphere.
EN 50019: Ignition protection category: increased safety »e«
Type of protection where additional measures are applied to electrical equipment
that does not produce arcs or sparks in normal operation, to give increased
security against the possibility of excessive temperatures and the occurrence of
arcs or sparks within the external or external parts of the electrical equipment.
EN 50020: Ignition protection category: intrinsic safety »i«
Type of protection where the electrical energy within the equipment is restricted
to a level below that which could cause ignition by sparking, arcing or
temperatures.
EN 50028: Ignition protection category: encapsulation »m«
Type of protection where parts that could ignite an explosive atmosphere by
either sparking or heating are enclosed in a compound in such a way that this
explosive atmosphere cannot be ignited.
ATEX & Intrinsic Safety Information - Explosive Atmospheres
Protection Concepts
ZONE
HAZARD
PROTECTION CONCEPTS
0
In which an explosive gas/air Exia or Exs
mixture is continuously
present for long periods
1
In which an explosive gas/air Exd. Exe, Exib, Exp, Exia, Exs
mixture is likely to occur in
normal operation.
2
In which an explosive gas/air All concepts suitable for
mixture is not likely to occur Zone 0 & 1, ExN, ExO and Exq
in normal operation.
Standards For Methods Of Protection
METHOD OF
PROTECTION
PERMITTED ZONE
CODE LETTER
OF USE IN UK
IEC, EX.., CENELEC, EEX
General requirement
-
-
Oil immersion
2
o
Pressurisation
1 or 2
p
Powder filling
2
q
Gas Grouping
Temperature Classification
GAS # GROUP
CENELEC
EN 50 014, 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
Associated
apparatus*
Certified
to the
CENELEC
standard
Explosion
protected
ia
]
Protection
Associated
concept (IS) apparatus*
IIC
T4
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
M1
–
Pit gas &/or flammable dusts
M2
–
II
G = gas
Other areas
1G
0, 1, 2
Explosive atmosphere
2G
1, 2
3G
2
D is added after G in the certification class
number
D = dust
(i.e. GD) if device is dust category approved
also
1D
20, 21, 22
2D
21, 22
3D
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
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