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. FAQ
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.