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Combustible Dust Extraction
Combustible Dust Application

Combustible dust

Explosive dust or potentially explosive atmospheres occur in a wide variety of workplaces

Due to the fact that dust from most organic materials, synthetic materials and metals can explode, attention needs to be given to prevent dust explosions. The European Community passed two directives on explosive atmospheres / combustible dust (called the ATEX directives), which came into effect on 1st July 2003 and July 1st 2006.

The application of these two directives has led to increased protection against explosions, making various technical and organisational actions obligatory. As leading experts in industrial air filtration, Nederman develops ATEX compliant products that fulfill the highest safety requirements.

Is Your Wood Waste Combustible? Watch us test several wood dust samples to see which explode and which do not.

Compliance with additional requirements in accordance with national or local government regulations are the responsibility of the local Nederman sales company and the customer.

Nederman offers dust extraction systems fulfilling the ATEX demands:

  • The explosion strength of the filter has been proven
  • ATEX compliance is ensured by means of explosion relief doors or panels
  • The risk of an explosion spreading may be prevented by installing safety equipment such as rotary valves, back pressure flaps, etc.
  • Fans are ATEX certified for handling potentially explosive dust.

Handling combustible dusts

End user responsibility

It is the owner/end user’s responsibility to determine the possible explosion risk in his premises. One of the obligations is to classify the areas where explosive atmospheres may occur. Another obligation of the owner/end user is to develop an “Explosion Protection Document”, that demonstrates amongst other:

  • Explosion risk and assessment
  • Adequate measures will be taken to attain the aims of the directive
  • The areas that have been classified into “zones”
  • That the workplace equipment is operated and maintained with due regards for safety

Only when the end user has declared the zones, will it be possible for the Nederman sales person to determine whether Nederman can provide the machinery and equipment required. The Nederman sales person will need the following data from the customer who will be the owner and end user of the equipment. 

  • The ATEX zone classification of the areas into which the equipment will be installed. This is the responsibility of the end user
  • The properties of the dust to be handled, including its explosion class St1, St2 or St3. 

ATEX zone classifications

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. Examples: In general these conditions arise only inside equipment such us pneumatic conveying lines, mills, dry mixers, sieves etc. Zone 20 atmosphere is typically found inside equipment.

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. Examples: In general, these conditions can arise where dust clouds are frequently present during normal operation, e.g. grinding, sanding, open charging etc. The extent of zone 21 atmosphere is typically a distance of 1 meter around the source of release. Human beings typically find it extremely difficult to breathe in zone 21 atmospheres. 

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. Examples: In general, these conditions can arise in places with dust lying on the floor and other surfaces which can be dispersed and form explosive dust clouds. Normally, a manned area or an area close to people is most likely to be a no-zone (safe – non hazardous) area. For the general area to be classified even as Zone 22 there could be considerable deposits of dust lying on surfaces. Zone 22 atmosphere can occur in places where dust can escape through leaks and form hazardous quantities, in bag storage areas (bag breakage) etc. The extent of zone 22 atmosphere is typically a distance of 1 m (3.28 ft) around the source of release. 

Manufacturer’s responsibility

It is the manufacturer’s responsibility to state the ATEX category of the machinery and equipment produced by the manufacturer. Products are categorized 1D, 2D and 3D with category 1D meaning the product employs a very high level of protection (zone 20, 21, or 22); category 2D, a high level of protection (zone 21 or 22); category 3D, a normal level of protection (zone 22). The Nederman symbol for products suitable for handling explosive dusts is Ex or Z.

If Nederman as the manufacturer determines that the equipment/filter unit etc. is intended to be installed in a classified area, the equipment must be marked according to the ATEX directive (2014/34/EU). 

CE mark

Above is an example of how Nederman equipment can be marked. Ex in a hexagon is the explosion protection symbol, followed by equipment group II (non mining), category 3D for Dust (D). Protection by constructional safety is represented by the “c”. Max surface temperature 125°C (257 °F). 

Nederman Customization of Products

Product customization can be done by Nederman as long as it does not jeopardize the safety (risk assessment) of the product. Enlarging the total volume and/or area of the filter unit could put the strength of the product at risk. Additional electrical components or similar equipment representing an ignition source must be categorized if they are to be placed in a hazardous area.

Dust classification 

The very same dust normally becomes more “explosive” the smaller the dust particles become. Therefore the properties of the dust to be handled in the Nederman equipment are of great importance. The specific KSt value or St class of the dust must therefore be provided by the customer. The KSt value is the maximum rate of explosion pressure rise in a 1 m3 (35,3 ft3) container. St classes are categories into which dusts are classified on the basis of their KSt values. 

Dust explosion class
KSt , bar m/s (psi ft/s) 
 St 1 > 0 to 200 (0–61)
 St 2
> 200 to 300 (61–91) 
 St 3
> 300 (91) 
 Table 1: St classes  

Nederman equipment installed outdoors is suitable for explosive dusts of class St1 or St2. The equipment is not suitable for gas, chemical instable dusts or materials that self ignite, e.g. magnesium.

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Products that solve: Combustible dust