What determines the class of a liquid as flammable or combustible?

The classification of a liquid as flammable or combustible primarily hinges on its closed cup flash point. The flash point is the lowest temperature at which vapors of a liquid can ignite when exposed to an open flame or spark in a controlled environment.

If the closed cup flash point is below 100°F (37.8°C), the liquid is categorized as flammable. Conversely, if the flash point is at or above that temperature, it is classified as combustible. This distinction is crucial for safety regulations, storage guidelines, and handling procedures in various environments, particularly those with fire hazards.

In contrast, while the type of container, the chemical structure of the liquid, and the storage environment can influence the behavior of a liquid when exposed to heat or flame, they do not directly determine its classification as flammable or combustible. The flash point provides a standardized measure that can be universally applied to classify liquids accurately. Understanding this classification helps ensure proper handling to minimize fire risks.