Relevance and advantage of the area classification in workplaces
The practice has been established of dividing potentially explosive atmospheres into zones. This classification takes the different dangers from explosive atmospheres into account and allows explosion protection measures to be taken which reflect the situation both from the point of view of safety engineering and of economic efficiency. For the European community, the zone definitions are uniformly provided in Directive 1999/92/EC. It must be applied with technical understanding of the specific situation.
Classification of hazardous areas
| Gases, vapours | |
|---|---|
| Zone 0 | area 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 | area 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 | area 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 |
| Dusts | |
|---|---|
| Zone 20 | area in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently |
| Zone 21 | area in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur, occasionally, in normal operation |
| Zone 22 | area 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 |
IEC 60079-10-1 assumes an approximately similar classification for gases and vapours which will also apply to facilities constructed in accordance with the US standard NEC 505. IEC 60079-10-2 provides support for the zone classification with dusts and will also apply to facilities constructed in accordance with the US standard NEC 506.
Potentially explosive atmospheres are classified depending on the frequency and duration of the explosive atmosphere. This classification provides the scope of the measures to be taken according to Annex II section A in the Directive 1999/92/EC in conjunction with equipment categories according to Annex I of the Directive 2014/34/EU.
In workplaces the potentially explosive atmospheres are normally classified at most as Zone 1 or 2 and 21 or 22. Zone 0 and 20 are restricted to very small inaccessible areas in work places or are usually restricted to the inside of technical equipment.
Organizational measures
The requisite preconditions for the safe operation of electrical equipment in potentially explosive atmospheres are created in a joint effort by the manufacturers of explosion protected equipment and the constructors and operators of industrial plants. It is important that the operator of such plants should ensure that their personnel know how the danger of explosions is likely to arise and the measures that are to be taken to prevent it.
The employees should be regularly trained on the contents of the explosion protection document in accordance with the Directive 1999/92/EC (occupational safety regulations) and informed by means of written corporate regulations which should be regularly updated.
Notes:
- Layers, deposits and heaps of combustible dust shall be considered as any other source which can form an explosive atmosphere.
- ‘Normal operation’ means the situation when installations are used within their design parameters
- The definitions for explosive atmospheres comply with the European directives and EN-IEC standards:
- Explosive atmosphere: this is a mixture of air and flammable substances in the form of gases, vapours, mists or dusts under atmospheric conditions in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
- Hazardous explosive atmosphere: this is an explosive atmosphere that causes damage on explosion, and which necessitates the introduction of measures to protect employees from explosion hazards.