flash point

Flash point:
A chemical's flash point is the lowest temperature at which the substance still gives off enough vapor to ignite when it comes into contact with an ignition source (such as a spark from a spark plug, or other glowing objects). Flash point should not be confused with auto-ignition temperature. This is the temperature at which a vapour/air mixture spontaneously ignites without the aid of an ignition source (which happens, for example, with engine knocking).
Gasoline fuel by itself does not ignite. However, when the gasoline has passed into vapor form, it does. This petrol vapor has a flash point of between -21 and 21 degrees Celsius.
Diesel presents less danger, because the flash point is above 75 degrees Celsius.