Since 2014, regulations have required new equipment installed in ATEX atmospheres to meet the requirements of Directive 2014/34/EU.
It covers the conformity of ATEX equipment and installations in industrial environments. Equipment must be marked as follows:
EX -> d -> II -> C -> T6
- Compliance with CENELEC (Ex) standard
- Equipment protection mode (d = explosion-proof enclosure)
- Classification of gas or dust groups (II = Gas)
- Subdivision of gas groups (C = Hydrogen)
- ATEX temperature class corresponding to maximum material surface temperature (T6 = 450°C)
It’s this last criterion that interests us. What are the specifics of ATEX temperature classes? The ADF Systèmes team explains.
ATEX temperature classes
In ATEX regulations, particular attention is paid to temperatures.
Indeed, the various substances, gases, gas vapors and dusts can self-ignite under the effect of a certain degree of heat.
Minimum ignition temperature is used for dusts, and self-ignition temperature for gases and vapors.
The lower these temperatures, the more dangerous a substance is.
Consequently, electrical devices for ATEX applications are classified according to the maximum surface temperature they generate. This must always be below the auto-ignition point.
Special features of gases and vapors
In the case of gases and vapours, a temperature classification system ranging from T1 to T6* is used:
- T1: 450°C
- T2: 300°C
- T3: 200°C
- T4: 135°C
- T5: 100°C
- T6: 85°C
*Marking according to IEC, CENELEC and NEC505.
In practical terms, this means that a T6-rated material will not exceed 85° surface temperature.
Dust specificities
For dust, the maximum surface temperature is specified directly on the marking: for example, T 129°C means that the equipment will not exceed a surface temperature of 129°C.
In the case of dust clouds, maximum surface temperatures must be less than or equal to ⅔ of the ignition temperature.
- Max temperature (C°) = 2/3 of the ignition temperature of a dust cloud (Tci)
In the case of dust layers, the temperature must be limited according to the presence of a dust layer of less than 5mm.
- Max. temperature = 5mm – 75 k (75 k corresponds to the safety coefficient of 75°C)
Finally, the temperature class or maximum surface temperature of ATEX equipment is only valid for a given ambient operating temperature.
It is therefore the responsibility of users to check that the equipment is designed for the temperature specified in the classification. This is one of the prerequisites for ensuring the safety of an industrial site with ATEX zones.
Would you like to find out more about ATEX temperature classes?
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