Question

What is the flash point of a material?

Answer 1

Hint: Try to figure out which characteristic is used to distinguish between a flammable fuel (such as gasoline) and a combustible fuel, such as diesel. The same characteristic is used to characterize the fire hazards of fuels.

Complete answer:
Every liquid in the environment has a specific vapour pressure (a function of liquid’s temperature) and each liquid is subject to Boyle’s law. We should know that, as temperature increases, the concentration of vapour of liquids in air increases. Thus, the temperature is the determining factor for the concentration of vapour of a liquid in air.
Now, coming to flash point. Flash point is that temperature, which is considered as the lowest temperature at which the vapours of a volatile material ignites if provided with an ignition source. It is used as a descriptive characteristic to differentiate between fuel (whether it is flammable or combustible). Fuels with less flash point less than ${{37.8}^{o}}C$ are called flammable fuels. Whereas, the fuels that have flash points above that temperature are considered as the combustible fuels. The flash point is also used to characterize any presence of fire hazards of fuels.
The flash point is considered as an empirical measurement rather than a fundamental physical one. It is an important concept used to fire investigation and fire protection because it is the lowest temperature at which risk of fire exists in a certain liquid.

Note:
It is important to note that flash point and autoignition point (temperature at which there is spontaneous ignition) are totally different. While the fire point is the lowest temperature at which the liquid’s vapour keeps burning even after the source of ignition is removed.