the lowest temperature at which a petroleum product will burn. Below this temperature insufficient petroleum vapour is available to support combustion. Before gasoline became important, kerosene was the main petroleum product produced. The tendency to leave as much of the highly volatile gasoline as possible in the kerosene caused numerous fires and explosions in tanks and oil lamps. Legal measures were instituted to curb the danger, and test methods were prescribed and minimum flash points set.

Minimum flash points have been set not only for kerosene and other volatile petroleum products but also for such low-volatility products as lubricating oil, diesel oil, and fuel oil. While such standards might be useful in providing the safety margins for storing, handling, or transporting high-volatility petroleum products, they are superfluous for those of low volatility. Probably this practice is a held-over tradition and is based on the belief that the flash point is a measure of volatility, a fact true only for products that boil over a narrow temperature range.