4 – Flammable gases, or very volatile flammable liquids with flash points below 73ºF, and boiling points below 100º F. Materials may ignite spontaneously with air.
3 – Materials capable of ignition under almost all normal temperature conditions. Includes flammable liquids with flash points below 73º F and boiling points above 100º F, as well as liquids with flash points between 73º F and 100º F.
2 – Materials which must be moderately heated or exposed to high ambient temperatures before ignition will occur. Includes liquids having a flash point at or above 100º F but below 200º F.
1 – Materials that must be preheated before ignition will occur. Includes liquid, solids, and semi-solids having a flash point above 200º F.
0 – Materials that will not burn.
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