ATEX Temperature Classes (T1–T6) – Complete Guide
TL;DR
T-class is the maximum external surface temperature a device may reach.
Pick a T-class that is lower than the auto-ignition temperature (AIT) of your atmosphere:
if AIT = 180 °C, choose T4 (≤135 °C) or cooler.
1 What temperature classes control
Temperature classes limit device surface temperature to prevent ignition by hot surfaces.
They do not cap process temperature or fluid set-point. You’ll find the T-class on the
EX nameplate and in the equipment certificate/datasheet.
2 ATEX/IEC T-classes (reference table)
| T-class | Max surface temp | Indicative substances* | Notes |
|---|---|---|---|
| T1 | ≤ 450 °C | Methane | Least stringent; many devices qualify. |
| T2 | ≤ 300 °C | Ethane, Ethylene oxide | Check motor/luminaire temperatures at high Ta. |
| T3 | ≤ 200 °C | Kerosene/Diesel vapours | Very common in process plants. |
| T4 | ≤ 135 °C | Ethyl ether, Acetaldehyde | Frequent for instruments & lighting. |
| T5 | ≤ 100 °C | — | Less common; limited power dissipation. |
| T6 | ≤ 85 °C | Carbon disulphide | Most stringent; careful thermal design required. |
*Examples are indicative only. Always compare a trusted AIT value for your gas/dust with the device T-class.
3 How to select the correct T-class (field workflow)
- Confirm the area’s classification (zone/EPL) from the site documentation.
- Identify the atmosphere and its auto-ignition temperature (AIT).
- Choose a device with T-class ≤ required limit (must be below the AIT).
- Check ambient rating (Ta): many devices derate T-class at higher Ta.
- Consider duty effects: VSDs, blocked filters, coatings and enclosures raise surface temp.
- Verify the nameplate and certificate match; record in the EX register.
4 Dust atmospheres note
Dust classification uses a direct temperature value (e.g., Ex tb IIIC T125°C Db)
rather than T1–T6. Consider dust layer thickness and insulating effects per EN/IEC 60079-14/-31.
5 Common pitfalls & audit findings
- Surface ≠ process: T-class limits only the equipment’s outer surface temperature.
- Ambient ignored: a device rated T4 at Ta 40 °C may fall to T3 at Ta 60 °C.
- Thermal changes after install: painting, insulation, or tight canopies can void T-class.
- Missing evidence: no datasheet/certificate attached to the Ex register.
6 FAQs
Is T4 always “safer” than T3?
Not necessarily—use the class that meets the AIT requirement. T4 is cooler but may be larger or costlier.
Where do I find the T-class?
On the EX nameplate and in the certificate/datasheet for the exact model and ambient.
7 Related reading
- Protection Concepts (Ex d, Ex e, Ex i, Ex p)
- How to Read an ATEX/IECEx Nameplate
- EX Zones explained
- EX Inspections – Types & Frequency
9 Conclusion
Selecting the right T-class is a simple but critical step: keep the device surface temperature below the atmosphere’s AIT, verify ambient limits, and document everything in your Ex register.
EXREG keeps those records audit-ready.
