13.8.1   Contamination by dust
Dust is defined as particulate air contaminants dispersed in gases and consisting of microscopically small particles of solids (frequent particle diameter 1 μm, largest particle diameter approx. 150 μm). Dust particles are transferred by air movement. Depending upon its action, dust is divided into the following types:
  • gap-filling dust (flour, tobacco, lime, cement, carbon black and coal dust)
     
  • abrasive dust (steel, silica, glass and hardwood dust)
     
  • chemically active dust (arsenic, lead, zinc, chemically aggressive rock dust etc.)
     
  • infectious dust (tubercle bacilli, anthrax spores)
Air in industrial zones contains on average 3,500 - 140,000 dust particles/dm. Many of the world's harbors are close to such centers of industry, and considerable quantities of dust may also be present in the air close to bulk cargo handling facilities.
 
Dusty goods do not only cause contamination, but they may also cause dust explosions, a phenomenon which must be taken into account in particular during the handling and transport of cereals and feedstuffs. All kinds of goods which release combustible dust may cause dust explosions, for example sugar, flour, cereals, mixed feedstuffs, coal, coke, lumber, sulfur etc.. The occurrence of dust explosions depends upon the nature and density of the dust and the presence of a thermal or electrical ignition source.
 
Dust-air mixtures constitute an explosion hazard at mixture ratios of 20 - 2,000 g/m of air. The pressure wave caused by localized ignition of an explosive dust-air mixture is propagated to adjacent layers of dust, which did not in themselves constitute a risk, and swirls up further dust-air mixtures, so resulting in secondary explosions.
 
For the purposes of packing and storing goods together, a distinction is drawn between those goods which are merely dusty and those which create so much dust that even packaged goods may suffer damage. The same applies to the passive behavior of the goods.
 

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