The National Fire Protection Association (NFPA) classifies diesel fuel as a Class II fuel. Class II fuels are not considered to be flammable liquids. They are, however, considered to be combustible liquids.
Flammable liquids have a flash point that does not exceed 100 degrees Fahrenheit, according to the NFPA. The U.S. Department of Transportation (DOT) considers the upper limits of flammable liquid fuels to reach 141 degrees Fahrenheit.
Combustible liquids have a flash point of 100 degrees Fahrenheit or greater. At this flash point, the liquid fuel can evaporate to form a combustible concentration of gas.
Class II liquids include diesel fuel, paint thinner, camphor oil, mineral spirits, and kerosene. The NFPA considers their flash point to be equal to or greater than 100 degrees Fahrenheit but less than 140 degrees Fahrenheit.
