Question

Flammable and combustible liquids are a fire hazard. What does combustible mean?

Answer 1

Combustible- A liquid with a flash point over $100^\circ F\left( {38^\circ C} \right)$ is considered combustible. Examples: diesel fuel, motor oil. Methanol is also a highly flammable liquid with a flash point between $11$ and $12^\circ C$. The primary use of methanol is as a base product for manufacturing chemicals such as formaldehyde.

Complete answer:
We must remember that a material is considered flammable if it has a flashpoint of any temperature below $37.8^\circ C$. A material is considered combustible if it has a flash point higher than $37.8^\circ C$ and below $93.3^\circ C$.
Flammable liquids are among the most common hazardous chemicals found in a laboratory. The primary hazard associated with flammable liquids is their ability to readily ignite and burn. The National Fire Protection Association (NFPA) defines a flammable liquid as a liquid whose flash point does not exceed $100^\circ F\left( {38^\circ C} \right)$.
Methanol is also a highly flammable liquid with a flash point between $11$ and $12^\circ C$. The primary use of methanol is as a base product for manufacturing chemicals such as formaldehyde which is then used to produce plastics, paints and explosives. Methanol is also used to fuel some performance vehicles. A combustible material is a solid or liquid that can be easily ignited and burned. OSHA, DOT, and other federal regulations, apply specific technical definitions to this term. Combustible solids are those capable of igniting and burning. Wood and paper are examples of such materials.

Note:
We need to know that the combustible liquids are classified as Class II and Class III, which are further sub-classified, based upon additional criteria that affect fire risk, as Class IIIA and Class IIIB - these liquids have flash points of $100^\circ F\left( {38^\circ C} \right)$ or more.