At what temperature do combustible liquids ignite?

The correct choice is the flash point. The flash point is defined as the lowest temperature at which a combustible liquid can produce enough vapor to ignite when exposed to an open flame or spark. It is crucial in fire safety and hazard classification because it indicates the potential flammability of a substance. Understanding the flash point helps firefighters and safety professionals determine the necessary precautions when handling combustible liquids in various environments.

In contrast, the fire point is the temperature at which a combustible liquid not only ignites but continues to burn for a specified period under controlled conditions. The auto-ignition temperature refers to the temperature at which a substance ignites without an external ignition source, and the boiling point is the temperature at which a liquid turns into vapor. While these temperatures are important in characterizing the behavior of combustible materials, they do not specifically define the minimum thermal conditions required for ignition as effectively as the flash point does.