ATEX air pollution control systems for potentially explosive atmospheres
An insight into the characteristics of ATEX industrial ventilation systems
In previous articles, we have already discussed ATEX themes, with a particular focus on Directive 2014/34/EU which, effective from 20 April 2016, repealed the previous Directive 94/9/EC. As we have seen, this directive aims to ensure the free movement of products within the European Community. To this end, the necessary requirements for all equipment and protective systems intended for use in potentially explosive atmospheres have been defined. But on a practical level, how should plants for use in potentially explosive atmospheres be designed?
What features must their components have? And what precautions are required when purchasing an ATEX system? The aim of this article is to answer these questions together.
ATEX zones
Before addressing the questions above, it is better to clarify two aspects related to the ATEX directive: what elements are necessary for a potentially explosive atmosphere to occur and the classification of ATEX zones.
The first aspect relates to the phenomenon of explosion: it occurs when fuel, oxidiser and a spark (ignition source) are present at the same time; additionally, dispersion and compartmentalisation must be considered in the case of dust. If even one of these elements is absent, we cannot speak of a potentially explosive atmosphere, and consequently, we are not covered by the ATEX directive.
Regarding the second aspect, hazardous working areas are divided based on the frequency and duration of the presence of explosive atmospheres due to gas (zone 0, 1 and 2) or dust (zone 20, 21 and 22).
In this article, we will focus on combustible dusts, and particularly on the zones mentioned below that can occur in abatement systems:
- Zone 20: a place 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: a place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally; a place in which an explosive atmosphere is likely to occur occasionally;
- Zone 22: a place 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.
Systems located in zones 20 or 21, due to their higher risk of explosion, must be certified by appropriate bodies and must be equipped with safety systems, resulting in increased construction costs.
Systems classified as zone 22 must be equipped with appropriate safety systems and the manufacturer must issue a self-certification stating that they comply with the ATEX directive.
KST and Pmax: dust explosion parameters
When designing ATEX industrial ventilation systems, one of the first considerations must be the characteristics of the dust to be treated. Among the main parameters to consider are:
- Kst = dust deflagration index, which measures the rate of pressure increase during the explosion of the specified dust. It is measured in bar m/sec. and also indicates the explosion expansion rate. The Kst is a key parameter for the sizing of safety panels, a theme which we will explore shortly;
- Pmax = indicates the maximum dust explosion pressure. It is measured in bar;
- LEL (Lower Explosion Limit) = the concentration of flammable gas or vapor in the air below which the gas atmosphere is not explosive;
- MIE (Minimum Ignition Energy) = is the lowest energy which, under specific test conditions, is capable of igniting the dust under test.
For more information, please read our dedicated article.
ATEX industrial ventilation systems: construction characteristics

Filters intended for use in ATEX atmospheres must be designed to withstand the explosion pressure, which varies depending on the characteristics of the dust and the production system. To this end, ATEX bag filters and/or cartridge filters, as well as activated carbon filters, are equipped with safety panels (explosion-proof or breakage protection panels) that, in the event of an explosion, open allowing the deflagration to be vented to the outside, thus preventing the filter from exploding. For this system to work, the filters must be designed to withstand higher pressures than the safety panels. Particular attention must also be paid to the dust discharge system, which must be made in an ATEX version in order to avoid generating sparks, while also acting as compartmentation equipment to contain the explosion within the system and not mechanically yield to the stress created.
One of the most widely used systems is the rotary valve: a component that allows the continuous discharge of dust from the hopper or scroll, preventing the pollutant from accumulating inside the filter. In its ATEX version, it is designed to avoid the generation of sparks.
For ATEX filtration and suction systems, there are also other components that are applied according to specific situations and needs. We will analyse some of them in the next section.
ATEX safety systems:
Safety non-return valve
The non-return valve is a device used to prevent the propagation of the explosion in the suction line and, consequently, in the production area. It is usually placed between the filter and the working environment and, in the event of a deflagration, it allows the shock wave to be blocked by letting the explosion vent through the explosion-proof panel.

Explosion diverters
Like the non-return valves, the explosion diverter is placed between the filter and the working environment to prevent the explosion from spreading into the production area. As shown in the picture below, in the event of an explosion, the flow path is diverted to vent the explosion in a safe environment. In some cases, the suction systems are equipped with a spark detection system, which provides an early warning of the risk of explosion, allowing for consequent flow diversion.

Fire dampers
Fire dampers are used to compartmentalise the airflow from the various production departments.
They are placed in the central suction pipe and, in the event of a fire, they intervene instantaneously, isolating the affected area and preventing the flames from spreading.
Explosion suppression system
The explosion suppression system can be compared to a firefighting system because it detects explosions in their initial phase and stops them quickly. In the event of a deflagration, a dedicated sensor sends a signal to the control centre, which commands the opening of the cylinders containing the explosion suppression agent in a few thousandths of a second. This mechanism is used as a second safety system in zones 20 and 21 and prevents a pressure buildup in the filter and its subsequent deflagration.
Flame arrester system (flame arrestors)
Flame arrestors are generally used when the abatement system is placed inside a warehouse: this system allows the flames to be contained, preventing them from deflagrating inside the workplace.
To this end, when designing a plant to be used in an explosive atmosphere, it is essential that all components (fan, pressure switch, piping, etc.) are designed according to the plant’s ATEX classification.
Conclusion: precautions for ATEX zone plants
We would like to conclude this article by answering the question we asked ourselves at the beginning, which is: what precautions are required when purchasing an ATEX industrial ventilation system?
First of all, it is essential to review the documentation issued by the supplier and ensure that all documents (user and maintenance manual, CE declaration, etc.) comply with the system’s application and, possibly with the area where the machine is to be installed.
Furthermore, based on what we have seen so far and the risks associated with explosive atmospheres, it is essential to rely on professionals who design the abatement systems taking into account the state of the affairs and equipping them with all the necessary safety systems.
For your next explosive dust treatment and suction system, choose the real experts: contact us to schedule an appointment with our specialised technicians!