When looking to protect your equipment against a dust explosion, it is critical that you know the Kst value of your material. Kst, is the dust deflagration index, and it measures the relative explosion severity compared to other dusts. This is a relative index, however, and any material with a Kst value greater than zero is considered to be at risk of an explosion. In fact, sugar has a relatively low Kst value, but was the fuel for for a massive explosion in 2008 that claimed the lives of 14 workers1.
Examples of Kst Values for Different Types of Dusts2
Dust explosion class*
Kst (bar.m/s)*
Characteristic*
Typical material**
St 0
0
No explosion
Silica
St 1
>0 and ≤ 200
Weak explosion
Powdered milk, charcoal, sulfur, sugar and zinc
St 2
>200 and ≤ 300
Strong explosion
Cellulose, wood flour, and poly methyl acrylate
St 3
>300
Very strong explosion
Anthraquinone, aluminum, and magnesium
The actual class is sample specific and will depend on varying
characteristics of the material such as particle size or moisture.
* OSHA CPL 03-00-008 - Combustible Dust National Emphasis Program.
** NFPA 68, Standard on Explosion Prevention by Deflagration Venting.
Additionally, you can search an extensive database of materials that provides Kst values. The values listed in these sources should be treated as theoretical values, as the explosiveness of dust is based on several other factors including particle size, moisture content, available oxygen, and dust concentration. Testing, with a lab such a Fauske is the only way to know the Kst value of a specific grade of a material.
