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Consequences of Dust in Bulk Materials Handling

Unlike material spillage, which generally stays close to the point on the conveyor where the material is released, airborne dust affects the entire operation. Once dust is released into the air, it will settle wherever the currents of air take it. There are many dangers, expenses, inconveniences, and inefficiencies associated with airborne dust.

It is in an operation’s legal and financial best interest to deal properly with dust.

When an operation violates a safety regulation, there are legal ramifications for the parties accountable (including personal culpability and possible financial liability for executives of operations where safety violations occur); therefore, there is a personal incentive to eliminate dust.

Health Risks

The greatest danger of dust is in the exposure of workers, neighboring homes, and businesses to dust. If the material is toxic, carcinogenic, or otherwise hazardous, having it airborne can endanger large numbers of people. In addition to the toxic dangers of materials, there is a respiratory danger presented by airborne dust. Once respirable dust is taken into the lungs, it might not be expelled. Prolonged exposure will lead to buildup of material in the lungs. Most regulating agencies define 10 microns as the size of respirable dust. When airborne particles 10 microns or smaller are inhaled, they will stay in the lungs; therefore, dust particles of 10 microns or smaller have a much lower allowable concentration. With toxic materials, the allowable concentration is even lower. In the United States, silica is normally regulated to the point where maximum allowable concentrations are below 2 milligrams per cubic meter (2.0 x 10.6 oz/ ft3) per eight­-hour day. Many government and private agencies have deemed that continued exposure to concentrations higher than these will cause silicosis.

OSHA has determined admissible dust levels for the United States. The levels determined by OSHA are representative of levels of regulation seen, and increasingly enforced, around the world.

Chart showing particle size to percentage passing sieve
Percentages of Particle Sizes Passing Through a 10-Micron Size-Selection Device

Explosion Risks

Another danger of dust is its potential for explosion. Materials that obviously have this potential are coal and other fuels. Even materials that are not flammable in their bulk state can combust when airborne as fine dust. For example, aluminum dust is flammable.

There are five contributing components necessary for a dust explosion to occur. The first three form the "triangle" of components of any fire:

  1. Fuel (ignitable dust)
  2. Ignition source (heat or electric spark)
  3. Oxidizer (oxygen in the air) The final two components are required to create a dust explosion:
  4. Suspension of the dust into a cloud (in sufficient quantity and concentration)
  5. Confinement of the dust cloud

If any one of these components is missing, there can be no explosion. Many businesses offer products and solutions to counter the requirements for explosion, but the control of ignitable dust will decrease the chance for explosion as well as increase the effectiveness of these products.

It is the responsibility of the plant owners and management to be aware of the explosive properties of material in its various states and to actively eliminate the potential for explosion.

Topics: Belt Conveyor Safety, Dust

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