What is a combustible liquid?

• A. A liquid with a flash point at or above 100°F.
• B. A liquid with a boiling point less than 30°F.
• C. A liquid that will decompose or become self-reactive under conditions of shock or pressure.
• D. A liquid having a flash point below 100°F and having a vapor pressure not exceeding 40 psi absolute.

Answer: (A)

Combustible liquids are defined by their flash point: the lowest temperature at which enough vapor is produced to form an ignitable mixture with air. If a liquid has a flash point at or above 100°F, it’s considered combustible because you typically need to heat it more before it can ignite. This distinguishes it from flammable liquids, which have flash points below 100°F and ignite more easily.

So the best description is a liquid with a flash point at or above 100°F. The other statements focus on unrelated properties (boiling point, or decomposition/self-reactivity) or mix in a vapor-pressure criterion that doesn’t define combustible liquids.