Explosion hazard zones
According to the regulations, the obligation to determine the explosion hazard zones rests with the investor, designer or user who decides on the technological process as part of the explosion hazard assessment. However, according to the decree issued by the polish Minister of Economy, the obligation to divide explosion endangered areas into zones rests with the employer, as part of the explosion risk assessment.
The determination of explosion hazard zones is a complex process and requires from experts undertaking this task the knowledge of relevant norms, technical standards or regulations, between which there are often certain correlations and discrepancies. In cases where different guidelines apply at the same time, it is important to maintain an appropriate hierarchy in their application and to consistently stick to the chosen path.
In general, the classification of explosion hazard zones, taking into account the probability and duration of an explosive atmosphere, is as follows:
Zone 0 – is an area in which an explosive atmosphere is present continuously for long periods of time or will ferquently occur.
Zone 1 – is an area in which an explosive atmosphere is likely to occur occasionally in normal operation. It may exist because of repair, maintenance operations, or leakage.
Zone 2 – is an area in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only. These areas only become hazardous in case of an accident or some unusual operating condition.
Zone 20 – is an area where hazardous atmosphere formed by dust, cloud in air is present continuously, for long periods, ferquently or dust layers may be formed.
Zone 21 – is an area where hazardous atmosphere formed by dust cloud in air is likely to occur in normal operation, but not frequently and only for short periods and layers or combustible dust will in general be present.
Zone 22 – is an area where hazardous atmosphere formed by dust cloud in air is not likely to occur in normal operation, and if so then for a short period only, either accumulations and layers of combustible dust are present.
It is important to remember that when classifying hazardous zones and determining their extent, it is necessary to take into account all factors (technical and organizational solutions) that influence the area in which the explosive atmosphere occurs. For example, factors that reduce the frequency and/or the extent of occurrence of explosive atmospheres can include:
- use of local dedusting systems
- carrying out cleaning activities
- providing adequate exhaust ventilation
- carrying out leakage checks
- use of stationary detection systems
- inerting an explosive atmosphere, etc.