What an ATEX zone expresses
Classification describes the foreseeable frequency and duration of an explosive atmosphere in an area. It helps guide equipment selection and other preventive measures. It is neither an instantaneous measurement nor a direct scale of severity. A less frequent zone can still involve very serious consequences if ignition occurs.
Related concept: Explosive atmospheres.
Gases, vapours and mists
Zones 0, 1 and 2 are used for these atmospheres. Zone 0 means continuous, prolonged or frequent presence; zone 1 means occasional formation during normal operation; zone 2 means formation is unlikely during that operation or short-lived if it occurs. Determining the extent requires study of releases, ventilation and actual conditions, rather than drawing a fixed radius for every item of equipment.
Combustible dusts
Zones 20, 21 and 22 follow equivalent logic for combustible dust clouds. Deposits are also considered because they may generate a cloud or contribute to a fire. Inadequate cleaning can alter the conditions that justified the plan. Equipment interiors, transfer points and the surroundings of possible leaks must be distinguished.
From classification to measures
The zone is one input for selecting suitable equipment, but substance group, temperature and other characteristics also matter. Electrical and non-electrical equipment, hot surfaces, static electricity and temporary work are reviewed. Signage communicates the presence of a risk; it does not replace correct equipment selection or control of tasks.
Example at a filling point
In a hypothetical example, a connection releases vapour during each filling operation and has local exhaust ventilation. The assessment considers the emission, extraction performance and conditions if extraction fails. If production increases or the solvent changes, the assumptions must be reviewed even though the filling point has not physically moved.
Misinterpretations
A momentary reading with no gas does not remove a zone. Nor does classifying an entire building as a precaution resolve the identification of sources and measures. The plan must have a documented technical basis and remain consistent with the installation. The European categories described must not be transferred automatically to classification systems in other jurisdictions.
