ATEX T-classes: what do T1 to T6 mean?
An ATEX fan may only be used if its maximum surface temperature remains below the auto-ignition temperature of the gas or dust present. That sounds straightforward, but in practice, many people are unsure which T-class they need. This article explains the system.
What is the T-class?
The temperature class (T-class) indicates the maximum surface temperature a device may reach under normal operating conditions and under foreseeable fault conditions. There are six classes:
| T-class | Max. surface temperature | Application area (example) |
|---|---|---|
| T1 | 450°C | Methane, propane, many industrial gases |
| T2 | 300°C | Ethanol, ammonia |
| T3 | 200°C | Petrol, some solvents |
| T4 | 135°C | Acetaldehydes, specific fine chemicals |
| T5 | 100°C | Carbon disulfide |
| T6 | 85°C | Ethyl nitrite (rare applications) |
T6 is the most stringent class: the surface temperature must never exceed 85°C. T1 is the least restrictive. In most industrial applications, T3 or T4 is sufficient.
Who determines the required T-class?
The T-class is determined by the end user or their ATEX specialist, based on the substances and/or gases present in the zone. The process is straightforward: identify which gas or dust is present → look up the auto-ignition temperature in an ATEX gas database or safety data sheet → select a T-class where the maximum surface temperature remains well below that value.
Example: in an environment containing petrol vapour (auto-ignition temperature 280°C), a minimum of T3 (max. 200°C) is required. T4, T5 or T6 are also permitted, but not necessarily required in practice.
T-classes for dust: different from gas
For dust, the system works differently. Rather than T-classes, the standard specifies the absolute maximum surface temperature in degrees Celsius, for example “T135°C”. For combined gas/dust certification, you may see markings such as T3/T135°C.
What does this mean for the fan?
The maximum surface temperature of an ATEX fan, across a range of operating conditions, must be documented by the manufacturer in accordance with EN 14986. Importantly, the temperature class of the fan as a whole is determined by the component with the highest surface temperature. In practice, this is often the motor, particularly in axial fans where the motor is located within the airstream.
When purchasing an ATEX fan, it is advisable to verify that the stated T-class is appropriate for the substances present in your application. If you are unsure which T-class you need, or have doubts about the correct specification, consult the relevant safety data sheets and engage an ATEX specialist if needed. For questions about our range of ATEX fans, feel free to contact us.
T-classes in the fan marking: an example
A complete marking example for an ATEX fan (gas): ⟨Ex⟩ II 2G h IIB T3 Gb. This reads as: group II (industrial installations), category 2G (zone 1), protection method h (constructional safety), gas group IIB, temperature class T3, EPL Gb.
A complete marking example for an ATEX fan (dust): ⟨Ex⟩ II 3D h IIIB T135 Dc IP55. This reads as: group II (industrial installations), category 3D (zone 22), protection method h (constructional safety), dust group IIIB, maximum surface temperature 135°C, EPL Dc.
Note on the protection method designation: newer certificates and markings use “h” (in accordance with ISO 80079-36, in force since 2019). On older documents you may still encounter the designation “c”, this refers to the same protection method (constructional safety), but under the previous notation. Both designations carry the same meaning; the difference reflects only the version of the standard under which the equipment was certified.
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