Flash Point

Flash Point:
A flash point of a chemical substance is the lowest temperature at which the substance emits enough vapor to ignite when exposed to an ignition source (think of a spark from a spark plug or other glowing objects). The flash point should not be confused with the autoignition temperature. This is the temperature at which a vapor/air mixture spontaneously ignites without the aid of an ignition source (as occurs with engine knocking).
Gasoline fuel does not ignite on its own. However, when the gasoline has evaporated into vapor, it does. This gasoline vapor has a flash point between -21 and 21 degrees Celsius.
Diesel poses less danger because its flash point is above 75 degrees Celsius.