Hazardous area equipment is specified in terms of the types of gases present, being:
 |
| Temperature Class |
T1 |
T2 |
T3 |
T4 |
T5 |
T6 |
|
| Maximum surface temperature (șC) |
<450 |
<300 |
<200 |
<135 |
<100 |
<85 |
|
| Minimum ignition temperature of gas (șC) |
>450 |
>300 |
>200 |
>135 |
>100 |
>85 |
|
| Minimum ignition temperature of dust (șC) |
>500 |
>350 |
>250 |
>185 |
>150 |
>135 |
|
Temperature classification takes into account the ignition temperature of the flammable gases present
in the particular environment.
Ambient temperatures are of course considered in this appraisal, however circumstances which may increase this surface temperature must also be taken into account.
For example, an enclosure shall over a period of time, collect a layer of dust on its surfaces. This shall increase the units overall operating and surface temperatures, to a point nearing the flash or combustion point of surrounding gases, liquids or dusts, then an explosive situation would occur.
For Group I classified electrical equipment, where coal dust can form a layer, the maximum surface temperature shall not exceed 150
șC. If this layer can be avoided through sealing or protection from the ingress of dust, the internal surfaces must not exceed 450șC equipment, temperatures are classified as per the following table.
Temperature classes T1 to T6 (AS 1280.1) are used for all protection techniques, and correspond to the electrical devices maximum operational temperature.
The better the equipment, the lower the rated surface temperature. In other words a rating of T4 is better than that of T2.
Therefore, those items certified as being T6, can be used in T1,
T2, T3, T5 and T6 gases.
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