Dust collection and ATEX in industrial facilities

In many sectors such as wood, plastics, food, chemicals, metal and pharmaceuticals, dust is generated during production. This dust must be collected for both worker health and product quality. However, much of this dust is combustible and can explode under certain conditions. An industrial dust collection system should therefore be treated not only as a filtration task, but also as an explosion safety matter.

How does a dust explosion occur?

A dust explosion requires combustible dust, oxygen and an ignition source. In addition, the dust being dispersed in the air at a sufficient concentration and contained within an enclosed volume turns the event from a fire into an explosion. In dust collection systems, especially inside the filter housing and ducts, these conditions can come together.

The properties of the dust are decisive in assessing the hazard. Values such as explosion severity (Kst), maximum explosion pressure (Pmax), minimum ignition energy and minimum ignition temperature are determined by laboratory tests. Design and protection measures are based on this data. Literature values can give an indication, but in critical cases it is sounder to work with test results for the dust actually produced at the facility.

The ATEX framework

In Europe and Türkiye, explosive atmospheres are addressed under two main regulatory frameworks:

• Directive 2014/34/EU: Covers equipment and protective systems intended for use in potentially explosive atmospheres. It sets out requirements for manufacturers.
• Directive 1999/92/EC: Covers the protection of workers in explosive atmospheres. It sets out requirements for employers.

In Türkiye, these directives have been transposed into legislation through national regulations. The employer is responsible for preparing the risk assessment and the explosion protection document. Areas containing combustible dust are classified as Zone 20, 21 and 22 according to how often an explosive dust cloud is likely to form. This classification takes the EN 60079-10-2 standard into account. Equipment must be selected with the category and marking appropriate to the zone.

Basic protection measures in a dust collection system

The protection strategy is built in two steps. First, ignition sources and the formation of explosive atmospheres are minimised. Then, if an explosion does occur, its effects are limited. The measures we often apply on site are:

• Earthing and equipotential bonding: Ducts, the filter housing and conductive parts are earthed against static build-up. Where necessary, antistatic filter elements are used.
• Explosion venting: Suitably sized explosion vent panels are fitted to the filter housing. Venting is directed to a safe area where no people are present.
• Explosion suppression: Where venting is not possible, for example for equipment inside a building, chemical suppression systems are considered.
• Isolation: Non-return flaps or isolation valves are used to prevent an explosion from propagating back through the ducts into the production area. At the dust discharge point, components such as rotary valves can perform this function.
• Spark detection and extinguishing: In processes with a risk of carrying sparks, detection and extinguishing systems are installed on the ductwork.

Which measures are needed depends on the properties of the dust, the filter volume and the layout. The solution is therefore determined separately for each facility. Protective systems such as explosion vent panels, suppression and isolation systems must have appropriate documentation under 2014/34/EU. These components are selected and sized using data from the filter manufacturer and the protection system supplier. After installation, it should also be checked that the system has been installed in line with the design assumptions.

Other design considerations

As important as explosion safety is the system's capture efficiency. If sufficient capture is not achieved at the dust source, dust spreads into the space and gradually accumulates on surfaces. Accumulated dust can be raised into the air after a minor incident and lead to a larger secondary explosion. A good collection system, together with regular cleaning, is therefore also the main means of reducing dust accumulation. In design, we pay attention to the following:

• Positioning hoods and extraction points close to the source and correctly
• Achieving a conveying velocity in the ducts that prevents dust from settling
• Avoiding long horizontal runs and sharp bends in the duct route that cause dust build-up
• Selecting the filter type and filter surface area to suit the dust
• Placing the filter unit outside the building where possible
• Selecting electrical equipment appropriate to the zone in which it is located

Operation of the system is also part of safety. Filter differential pressure should be monitored, the dust hopper emptied regularly, and explosion panels and isolation components inspected periodically.

Care is also needed in existing facilities. Adding a new machine, increasing the number of extraction points or changing the raw material can alter both the system's capture performance and its explosion risk. Before such changes:

• The suitability of fan capacity and duct velocities for the new situation should be checked.
• The properties of the new dust should be compared with the existing protection measures.
• The risk assessment and the explosion protection document should be updated.

In facilities with combustible dust, a dust collection system operates safely and efficiently when process, occupational safety and mechanical design are considered together. The facility owner's risk assessment and explosion protection document are the key inputs to this design. At Ekura, we can provide support within this framework at the design, supply, installation and commissioning stages of dust collection systems.