Flash point

Flash point:
The flash point of a chemical substance is the lowest temperature at which the substance still gives off enough vapour to ignite when it comes into contact with an ignition source (think of a spark plug spark or other glowing objects). The flash point should not be confused with the auto-ignition temperature. This is the temperature at which a vapour/air mixture spontaneously ignites without the help of an ignition source (which is what happens, for example, with engine knocking).
Petrol (gasoline) fuel by itself does not ignite. However, when the petrol has turned into vapour, it does. This petrol vapour has a flash point between -21 and 21 degrees Celsius.
Diesel is less hazardous because its flash point is above 75 degrees Celsius.