ATEX systems and dust extraction

What are ATEX systems and why are they fundamental in the dust extraction sector? We talk about it in this article, explaining what it is and what their main applications are.

What are ATEX systems

ATEX systems are explosion-proof equipment and production systems. The European Union, as part of the risk due to the presence of potentially explosive atmospheres, has adopted two directives on health and safety, known as ATEX 2014/34/EU (also ATEX 114) and ATEX 1999/92/EC (also ATEX 153) which define the safety standards to be respected for machinery, systems and workplaces in the presence of potentially explosive atmospheres.

In more detail, environments at risk of explosion can be considered as such due to the presence of potentially explosive gases or dusts. In the specific case of dust, which we focus on in this article, the risk zones are classified as follows:

• Zone 20 = area where there is permanently or for long periods or often an explosive atmosphere in the form of a cloud of combustible dust in the air; 
• Zone 21 = area where occasionally during normal activities the formation of an explosive atmosphere in the form of a cloud of combustible dust in the air is likely;
• Zone 22 = area where during normal activities the formation of an explosive atmosphere in the form of a cloud of combustible dust is not likely and, if it occurs, is only short-lived.

ATEX systems, therefore, are designed and manufactured to be explosion-proof. Depending on the risk zone in which they are located, they must have specific characteristics:

• Installations in zone 20 or 21 must be certified by competent bodies in the field and must be equipped with double safety systems.
• The systems located in zone 22 require only one safety system and compliance with the ATEX directive can be attested by self-certification.

Applications in the dust extraction sector

ATEX systems therefore find important applications in the field of dust extraction. In particular, ATEX dedusting filters are designed to withstand overpressure due to dust explosion in the environment in which they are located.

The destructive capacity of a dust varies according to the characteristics of the dust itself and the environment, according to two parameters:

• KST: the parameter that measures the rate of increase in pressure in the specified dust explosion and which therefore also gives an indication of the speed of expansion of the flames associated with the explosion; 
• PMAX: the parameter that measures the maximum pressure developed in the explosion of a specific dust.

For this reason, ATEX systems are built considering these criteria, with the aim of ensuring adequate explosion resistance.

In the specific case of ATEX bag filters, it is essential to provide safety devices such as ATEX explosion vents that open in the event of an explosion, allowing the explosion to propagate outside and avoiding the explosion of the filter itself.

The dust discharge system must also comply with the ATEX standard. One of the most widespread systems is the rotary valve, made in such a way as not to allow the generation of sparks that can trigger an explosion; in some specific cases, it is also necessary to use certified rotary compartment valves.

Additional safety components in ATEX systems, used according to needs, may include: 

• Safety non-return valves and explosion diverters. Protection systems placed between the filter and the working environment to prevent the explosion from spreading in the production area.
• Explosion suppression devices. It detects explosions as soon as they are generated and nips them in the bud in a fraction of a second. In essence, this is the second safety system provided for by the ATEX directive in zones 20 and 21, which we mentioned above.
• Flameless venting: it is a safety device that is usually used in cases where the filter is located inside an industrial plant. Its purpose, in the event of an explosion, is to prevent the flame from spreading inside the plant, protecting the safety of workers and the production environment.

A final consideration to be made concerning ATEX systems is of a more general nature. To ensure the safety of machinery and workplaces, in fact, not only the filters but all the components of the system must be designed and built respecting the safety parameters provided for by the directive, according to the reference risk area.