Classification of Flammability
The US Government uses the Hazardous Materials Identification System (HMIS) standard for flammability ratings, as do many US regulatory agencies, and also the US National Fire Protection Association (NFPA).
The ratings are as follows:
| Rating | Degree of flammability | Examples |
|---|---|---|
| 0 | Materials that will not burn | water |
| 1 | Materials that must be preheated before they will ignite | lubricating oils, cooking oils |
| 2 | Materials that must be moderately heated or exposed to relatively high ambient temperatures before they will ignite | diesel fuel |
| 3 | Liquids and solids that can ignite under almost all temperature conditions | gasoline, acetone |
| 4 | Materials which will rapidly vaporize at atmospheric pressure and normal temperatures, or are readily dispersed in air and which burn readily | natural gas, propane, butane |
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