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The Importance of Explosive Dust Inspection

ATEC has recently completed a potentially explosive Dust Inspection at a local polymer plant that was Classed under NEC. Any combustible material can burn rapidly when in a finely divided form. If such a dust is suspended in air in the right concentration, under certain conditions, it can become explosible. Even materials that do not burn in larger pieces (such as aluminum or iron), given the proper conditions, can be explosible in dust form.

The force from such an explosion can cause employee deaths, injuries, and destruction of entire buildings. For example, 3 workers were killed in a 2010 titanium dust explosion in West Virginia, and 14 workers were killed in a 2008 sugar dust explosion in Georgia. The U.S. Chemical Safety and Hazard Investigation Board (CSB) identified 281 combustible dust incidents between 1980 and 2005 that led to the deaths of 119 workers, injured 718, and extensively damaged numerous industrial facilities.

A wide variety of materials that can be explosible in dust form exist in many industries. Examples of these materials include: food (e.g., candy, sugar, spice, starch, flour, feed), grain, tobacco, plastics, wood, paper, pulp, rubber, pesticides, pharmaceuticals, dyes, coal, metals (e.g., aluminum, chromium, iron, magnesium, and zinc). These materials are used in a wide range of industries and processes, such as agriculture, chemical manufacturing, pharmaceutical production, furniture, textiles, fossil fuel power generation, recycling operations, and metal working and processing which includes additive manufacturing and 3D printing.

Class II, Division 1 - Combustible dust is in the air under normal operating conditions in quantities sufficient to produce explosive or ignitible mixtures.

Class II, Division 2 - Combustible dust due to abnormal operations may be present in the air in quantities sufficient to produce explosive or ignitible mixtures.

Class III, Division 1 is a location in which easily ignitible fibers/flyings are handled, manufactured, thick dust! Such locations usually include some parts of rayon, cotton, and other textile mills; combustible fibers/ flyings manufacturing and processing plants; cotton gins and cotton-seed mills; flax-processing plants; clothing manufacturing plants; woodworking plants; and establishments and industries involving similar hazardous processes or conditions. No Groupings.

Class II atmospheric hazards cover three groups of combustible dusts, summarized:

  1. Electrically Conductive (Metallic) Dusts are Group E such as powdered metals such as Aluminum or Magnesium only classed as Division 1 only.
  2. Carbonaceous Dusts are Group F such as Carbon Black, Coal Dust, Coke Dust.
  3. Agricultural Dust (Organic) are Group G such as Grain, Flour, Sugars, Spices, Rice, Certain Polymers.

Demonstration of an open-air dust explosion

  1. Experimental setup
  2. Finely-ground flour is dispersed
  3. Cloud of flour is ignited
  4. Fireball spreads rapidly
  5. Intense radiant heat has nothing to ignite here
  6. Fireball and superheated gases rise
  7. Aftermath of explosion, with unburned flour on the ground