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Is My Dust Combustible?
When looking to protect your equipment against a dust explosion, it is critical to 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. Other than silicon or sand, every kind of dust is potentially combustible to some degree.
Examples of Kst Values for Different Types of Dusts
| Dust explosion class* | Kst (bar.m/s)* | Characteristic* | Typical material** |
| St 0 | 0 | No explosion | Silica |
| St 1 | >0 and ≤00 | Weak explosion | Powdered milk, charcoal, sulfur, sugar, zinc |
| St 2 | >200 and ≤200 | Strong explosion | Cellulose, wood flour, polymethyl acrylate |
| St 3 | >300 | Very strong explosion | Anthraquinone, aluminum, magnesium |
The actual class is sample specific and will depend on varying characteristics of the material such as particle size or moisture. Source: http://www.osha.gov/Publications/3371combustible-dust.pdf * OSHA CPL 03-00-008 – Combustible Dust National Emphasis Program. ** NFPA 68, Standard on Explosion Prevention by Deflagration Venting.
Kst Values for Common Dusts:
Any value greater than zero is a potential explosion risk
| Dust | KSt Value | Characteristic |
| Activated carbon | 44 | Weak Explosion |
| Aluminum grit | 100 | Weak Explosion |
| Aluminum powder | 400 | Very Strong Explosion |
| Asphalt | 117 | Weak Explosion |
| Barley grain dust | 240 | Strong Explosion |
| Bronze | 31 | Weak Explosion |
| Brown coal | 123 | Weak Explosion |
| Calcium stearate | 132 | Weak Explosion |
| Cellulose pulp | 62 | Weak Explosion |
| Cellulose | 229 | Strong Explosion |
| Corn | 75 | Weak Explosion |
| Charcoal | 117 | Weak Explosion |
| Cotton | 24 | Weak Explosion |
| Dextrin | 106 | Weak Explosion |
| Egg White | 38 | Weak Explosion |
| Epoxy powder | 125 | Weak Explosion |
| Epoxy resin | 129 | Weak Explosion |
| Flour, Bakers 4.3% Moist | 112 | Weak Explosion |
| Lead stearate | 152 | Weak Explosion |
| Magnesium | 508 | Very Strong Explosion |
| Malt dust | 122 | Weak Explosion |
| Melamine resin | 110 | Weak Explosion |
| Methyl cellulose | 209 | Strong Explosion |
| Milk powder | 90 | Weak Explosion |
| Paper tissue dust | 52 | Weak Explosion |
| Para formaldehyde | 178 | Weak Explosion |
| Peat | 178 | Weak Explosion |
| Pectin | 162 | Weak Explosion |
| Phenolic resin | 129 | Weak Explosion |
| Polyester | 85 | Weak Explosion |
| Polyethylene | 134 | Weak Explosion |
| Polyurethane | 156 | Weak Explosion |
| Rice starch | 190 | Weak Explosion |
| Silicon | 126 | Weak Explosion |
| Soap | 111 | Weak Explosion |
| Sodium ascorbate | 119 | Weak Explosion |
| Sodium stearate | 123 | Weak Explosion |
| Soot | 26 | Weak Explosion |
| Soybean flour | 110 | Weak Explosion |
| Starch, corn | 202 | Strong Explosion |
| Sugar | 138 | Weak Explosion |
| Sulfur | 151 | Weak Explosion |
| Tobacco | 12 | Weak Explosion |
| Toner | 145 | Weak Explosion |
| Wood dust | 102 | Weak Explosion |
| Wood Flour | 205 | Strong Explosion |
| Zinc | 176 | Weak Explosion |
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