Definition of a Highly Flammable Liquid (HFL)

A Highly Flammable Liquid (HFL) is a liquid with a flash point below 32 deg C. The flash point of a liquid is the lowest temperature at which the liquid can evaporate to produce vapour in sufficient concentration to form a combustible mixture with air near the surface of the liquid.  The flash points of some common laboratory solvents are:

Solvent Type Temp (Deg C) Temp (Deg F)
ethanol +12 53.6
toluene  +4 39.2
acetone -19 -2.2
carbon disulphide -30 -22
diethyl ether -45 -49

As the flash points of all these liquids are below average ambient room temperature the liquids will always constitute a fire and explosion hazard.  As an example the last three liquids listed above have flash points below the temperatures usually found in a refrigerator or freezer and will therefore constitute an explosion hazard even when in cold storage.

The Flash point is not the temperature at which a substance will ignite spontaneously. It is an indication of the ease with which a substance will burn if the vapours are exposed to a temperature at or above its auto-ignition temperature.