What are the explosion risk zones?

Industrial production involves some risk factors. One of such risks is dusted air, which may not only badly influence the health of people working in such area but it may also lead to dangerous explosions. In order to be able to react to such situations adequately, it is neccessary to define the so called explosion risk zones. What we should know about them?

What is the explosion risk zone?

An explosion risk zone is the area within the premises of a production plant where there is a risk that the explosion hazard atmosphere occurs. Explosion hazard atmospheere is defined as a mixture of dangerous substances in their minimum concentration necessary to support their combustion in the air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.

The difference between the explosivity limits depends on the type of the substance spread in the air – for some materials it is very small, for others it is much wider. If the concentration of the substances is below their minimum explosivity limit, there is no risk of explosion as there is not enough substance in the air for the combustion to take place. If the concentration of the substances is above the explosivity level, it means that there is too much of the substance and too little oxygene for the explosion to occur.

Identification of explosion zones

According to the European Directive known as ATEX (from French Atmosphères Explosibles), there are six types of explosion risk zones, however in industrial dedusting systems only three of them apply – the rest concerns installations for gases, liquids and fumes.

Here are the explosion risk zones which are present at different parts of dedusting installations:

• zone 20 – it includes devices, in which the risk of explosion is high, where an explosive atmosphere in the form of a cloud of combustible dust in the air is present continuously, long or frequently. This group includes the dust collector internal chamber with filter bags, outlet and expansion chambers, and chambers with decompressive panels
• zone 21 – It is where an explosive atmosphere in the form of a cloud of combustible dust in the air may occasionally occur during normal operation. It can be present inside pipelines and other elements on the dirty side of the installation (dirty side meant by dusted air side)
• zone 22 – it is where an explosive atmosphere in the form of combustible dust in the air is not likely to occur in normal operation but, in case when it does occur, it persists for a short time only. This zone includes, among others, extraction fans chamber, regeneration fans chamber and the clean air outlet.

Protection elements

Any explosion inside a dedusting installation causes enormous danger for the people working nearby and for the facilities such as builidings, machines etc. In order to avoid such situations or minimize their consequences, dedusting installations should be equipped with adequate explosion protective systems in accordance with the ATEX directive. Among the protective devices are explosion flap valves (installed between the dust collector and dirty air piplines to prevent the explosion from spreading to other elements of the dedusting system) or explosion decompression panels, which work as controlled venting of the fire and explosion pressure to a safe area.

Dedusting systems play significant role in providing safe functioning of industrial production plants. However, dust collectors also need to be protected against explosion, therefore, a correctly executed design, with certified technologies and professional execution are the warranty that the dedusting installation shall work in accordance with its intended use. If you need a professional and safe dedusting system, contact us!