Please see their definitions: Flash point The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. (i.e. the lowest temp to start a fire) At the flash point, the vapor may cease to burn when the source of ignition is removed. Autoignition temperature The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. In fact my question is not directly related to the above information, Can anyone tell me why a fire is needed to "start another fire" at the flash pt but not at the autoignition temp? Let's take an example, You have a lighter,you generate a flame and you can "transfer" it onto a candle wick or to a gas stove if the fuels stored in the stove doesn't combust. In this case the conditions to start a fire are reached(fuel,O2,temperature reaches flash point,according to the fire triangle) Now,imagine there isn't any source of ignition(sparks or flame),but the ambient temp is very high(lower than the autoignition temp and higher than the flash point),the candle wax will only melt but it will not burn,similar case in the gas stove,that is nothing will burn. What is the use of fire?Why does a fire is needed to start another fire at flash point?