Dust Explosions

Dust explosions (ATEX)

When combustible dust or powder swirls up and mixes with air, an explosive atmosphere can be created which explodes upon ignition. An explosive atmosphere is a mixture of air and combustible matter that can explode if ignited. The mixing ratio between dust – air and the size of the particles is crucial. Very small and fine particles increase the risk of explosion. Areas, where explosive atmospheres can form, are classified into zones. Dust zones are defined as ATEX dust zones 20, 21, and 22. Gas zones are defined as ATEX gas zones 0, 1, and 2. Read more about gas zones here↵. (Norwegian page)
Støveksplosjonspentagram

What is an explosive atmosphere?

An explosive atmosphere is an accumulation of gas, liquid mist, dust, or vapor mixed with air in a mixture that is explosive and can ignite with an ignition source.

A combustible atmosphere does not always have to end in a pure explosion. If the combustible mixture ignites, the flames will be able to spread quickly through the combustible atmosphere. Suppose this happens in a closed area, for example, in a processing plant or inside the equipment. In that case, the rapid spread and increase in pressure, among other things due to turbulence, could lead to the combustion increasing in speed and appearing like an explosion. The explosion pressure can also cause damage and flames from the combustion process.

Basic Technical Concepts

ATEX Dust zones

Dust zone 20

  • An area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present continuously, or for long periods or frequently.

Dust zone 21

  • An area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is likely to occur in normal operation occasionally.

Dust zone 22

  • An area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

ATEX Gas zones

Gas zone 0

  • An area in which an explosive gas atmosphere is present continuously or for long periods or frequently.

Gas zone 1

  • An area in which an explosive gas atmosphere is likely to occur periodically or occasionally in normal operation.

Gas zone 2

  • An area in which an explosive gas atmosphere is not likely to occur in normal operation, but if it does occur, it will exist for a short period only.

Ignition sources

A dust explosion can be triggered by:

  • Fire – open flames.
  • smoldering fire.
  • Auto-ignition in powder.
  • In dust layers on hot surfaces.
  • Mechanical sparks from friction in machine parts or from grinding.
  • Electric sparks.
  • Discharge by static electricity from plastic surfaces (pipes and containers), textiles, and equipment

You can find a lot of relevant information on the Norwegian labour inspection authority website↵.

Typical exposed areas

  • Typical exposed areas
  • Mills (Flour, grain, etc.)
  • Conveyor belts
  • Food production plant
  • Coal mines
  • Sawmills
  • Silos

Simulation of dust explosion with flour.

Støveksplosjon med mel
Støveksplosjon med mel 2
Støveksplosjon med mel 3
Støveksplosjon med mel 4

Pictures – Creative Commons Attribution-Share Alike 3.0 – Hans-Peter Scholz

Requirements and certification

There are very high requirements for equipment that has been certified for use in both ATEX gas zones and ATEX dust zones. We are proud to have a 3-part ATEX certification for both ATEX Gas Zones 1 and 2 and ATEX dust zones 21 and 22. You can use Safety Tools Allmet in all the previously mentioned typically exposed areas. The tools also generate no airborne dust during use. All fragments fall near your work area, and no surrounding equipment is not damaged. The removed fragments are easy to clean after finishing work, and the fragments are not sharp.

0047 jpg side 2