| Zone 0 |
0 |
A zone in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently. |
| Zone 1 |
1 |
A zone in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally. |
| Zone 2 |
2 |
A zone in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only. |
| Zone 20 |
3 |
A zone in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, for long periods or frequently. |
| Zone 21 |
4 |
A zone in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally. |
| Zone 22 |
5 |
A zone in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only. |