Taking the line apart
| Part | Example | What it says |
|---|---|---|
| Group | II | I mining (firedamp), II surface, III dust |
| Category | 2 | 1 → zone 0/20, 2 → zone 1/21, 3 → zone 2/22 |
| Atmosphere | G | G gas/vapour/mist, D dust |
| Protection type | db | How ignition is prevented (flameproof, increased safety, intrinsic safety…) |
| Gas group | IIB | IIA, IIB, IIC — IIC most demanding |
| Temperature class | T4 | Maximum surface temperature 135 °C |
| Protection level | Gb | Ga/Gb/Gc for gas; Da/Db/Dc for dust |
Matching is done part by part
It is not enough that the marking says “Ex”. Zone against category, the gas present against the group, the substance's ignition temperature against the T class — each is compared separately. If one of the three does not hold, the equipment is unsuitable for that zone even if the other two do.
Other information in the marking
- Ambient temperature range — outside it, the temperature class is not guaranteed.
- Certificate number — an X suffix means special conditions of use, a U suffix means it is a component and cannot be used on its own.
- Ingress protection — against dust and water, decisive in dust zones in particular.
What goes into the record
The equipment list records not just make and model but the whole marking line. A model number answers no question at the next inspection; the marking line answers all of them.