According to 29 CFR 1910.106, OSHA defines a combustible liquid any liquid having a flashpoint at or above 100°F (37.8°C). Combustible liquids are divided into two classes:

• Class II liquids include those liquids with flashpoints at or above 100°F (37.8°C) and below 140°F (60°C), except any mixture having components with flashpoints of 200°F (93.3°C) or higher, the volume of which make up 99% or more of the total volume of the mixture
• Class III: liquids with flashpoints at or above 140°F (60° C) and are subdivided into two subclasses
• Class IIIA: liquids with flashpoints at or above 140°F (60°C) and below 200°F (93.3°C), except any mixture having components with flashpoints of 200°F (93.3°C), or higher, the total volume of which make up 99% or more of the total volume of the mixture.
• Class IIIB: liquids with flashpoints at or above 200°F (93.3°C). OSHA’s combustible liquids standard does not cover Class IIIB liquids. Where the term “Class III liquids” is used in this portion of the OSHA regulations, it refers only Class IIIA liquids

 When a combustible liquid is heated for use to within 30°F (16.7°C) of its flashpoint, it must be handled in accordance with the requirements for the next lower class of liquids. This could result in a Class II liquid being treated as a flammable liquid as a result of being heated.