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How installations are zoned where dust or gas can ignite, and what that means for you as an operator
Many processes in industry handle substances that under the right — or rather wrong — conditions can form an explosive atmosphere: a mixture of air and a flammable substance as gas vapour or dust that can ignite and explode. Rules on this are collected under the term ATEX and they are a fixed part of the working environment in large parts of the process industry.
The Labour Authority's rules on explosive atmospheres require that areas at risk for explosive atmospheres be classified into zones depending on how frequently and how long the risk is present. For gas vapor and mist zones 0 1 and 2 are used. For dust zones 20 21 and 22 are used.
| Zone | Type | How often is the atmosphere explosive |
|---|---|---|
| 0 / 20 | Gas / dust | Constant or for long periods |
| 1 / 21 | Gas / dust | At regular intervals during normal operation |
| 2 / 22 | Gas / dust | Rarely if at all and only for a short time if it happens |
It is the company itself that is responsible for classifying the zones on its own premises. This happens as part of the mandatory workplace assessment — a so-called ATEX workplace assessment — where the risk of explosive atmosphere is identified, and where the technical and organisational measures that must protect the employees are determined.
In a classified area of the system, stricter rules apply to behaviour: unapproved electronics like an ordinary mobile phone have no place there, tools must be spark-free, and clothing and footwear should be antistatic so you do not yourself charge static electricity that could trigger a spark. If you are in doubt about what applies in a particular area, the answer is always to ask before you enter.
“An explosive atmosphere is not visible. That is precisely why rules about zones and approved equipment exist.”