Friday, January 7, 2011

Combustible Dust Laboratory Testing Primer

Potential combustible dust fires and explosions in the manufacturing, non-manufacturing, and utility sectors is a global problem. Across international borders the occupational safety regulatory standards for addressing combustible dust fire and explosion hazards varies. In contrast, the laboratory equipment in evaluating the hazard for ignition sensitivity and explosion severity is uniform with minor differences in methodology. For example, the 20 liter sphere is utilized worldwide in obtaining vital information on the maximum pressure and deflagration index (Kst) of combustible dust.

An excellent depiction of a dust explosion shown in the high speed video, shot at 600 frames per second, with 1 gram of custard powder dispersed in a glass tube past a hot coil ignition source. The glass tube has a volume of 1.2 litres, providing an explosive dust concentration of approximately 830 g/m3. Notice how the explosion pressure wave drives the dust ahead of it and out of the tube and debris from the explosion - mostly pieces of unburnt powder - continue to fall for some time afterwards. The second video sequence shows the same quantity of custard powder being ignited, but viewed from above. Note the thin plastic film held across the tube opening that acts as an explosion relief vent.

The catastrophic Imperial Sugar Refinery dust explosion in 2008 reminded global stakeholders how devastating industrial dust explosions can be. Measuring the explosive properties of the material being handled is, of course, the essential first step to understanding the hazard. Michael Ward of Explosion Hazard Testing in the U.K. has written an educational and very useful guide to explain combustible dust testing and what the lab results tell us in terms of explosion prevention and protection options.

The main points that the guide discusses:

  • UK statistics for fire and explosion
  • What a dust explosion is and the terminology involved
  • What laboratory tests are available and how they are conducted
  • What they tell us about the fire and explosive properties of the material
  • What tests are considered mandatory under U.K. and and EU legislation

The dust testing guide can be downloaded for free here


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