# Temperature Classes
#fundamental #hazardous-area #safety
Temperature classes (T1-T6) define the maximum surface temperature that electrical equipment can reach in hazardous areas without igniting surrounding flammable gases or vapors.
## Temperature Classifications
| Class | Max Surface Temperature | Typical Gases |
|-------|------------------------|---------------|
| T1 | 450°C | Methane, Propane, Acetone |
| T2 | 300°C | Ethylene, Butane |
| T3 | 200°C | Gasoline, Diesel, Kerosene |
| T4 | 135°C | Acetaldehyde |
| T5 | 100°C | Carbon disulfide |
| T6 | 85°C | Carbon disulfide |
## Key Principles
- Temperature class must be lower than the auto-ignition temperature (AIT) of the gas
- T4-approved instruments are sufficient for most applications
- Carbon disulfide (CS2) is the only common substance with AIT below 100°C
- Methane has an AIT of 595°C, so even T1 devices are sufficient
## Selection Criteria
Equipment temperature class must be appropriate for the gases present:
- Equipment with T3 rating cannot be used for gases with AIT < 200°C
- Ethers and aldehydes have AITs below 200°C
- T4 devices are typically adequate unless CS2 is present
## Diagram
*Table showing temperature classes (T1-T6), maximum surface temperatures, explosion groups, and typical gases for each classification*
## Related Concepts
- [[Auto Ignition Temperature - AIT]]
- [[Hazardous Area Classification]]
- [[ATEX]]