How do I know if my dust is combustible?

The combustibility of dust depends on a number of factors. For a quick check, look at this chart from the Occupational Safety and Health Administration (OSHA). If your dust is on that list, then you need to be concerned about combustible dust.

Just how combustible your dust is, however, depends on many things you won’t find on that list nor be able to see in your facility. For example, particle size has a major impact on the combustibility of a dust. In general, the smaller the particle, the more dangerous the dust.

To understand the specific dangers of your dust, it is best to have it tested by professionals. They can analyze a sample of your dust and produce a full report describing it. Their report would include two key numbers: the Pmax and Kst values. These numbers measure the explosive power of your airborne dust. The Pmax value is the maximum pressure that might be produced by an explosion of your dust. The Kst value—also called the deflagration index, measuring the relative severity of the explosion—is determined by several factors, including the size and chemical nature of your particulates, along with their moisture level.

Having at least a cursory understanding of these values is useful in assessing the risks. For example, the larger the Kst value, the stronger the possible explosion. A Kst value of 0 will result in no explosion. A value over 0 and below 200 could result in a “weak explosion.” A value between 200 and 300 could result in a “strong explosion.” These substances might include cellulose or wood flour. A value over 300 could see a “very strong explosion.” These materials might include aluminum or magnesium dust.


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