The lower flammability limit (LFL), usually expressed in volume per cent, is the lower end of the concentration range over which a flammable mixture of gas or vapour in air can be ignited at a given temperature and pressure. The flammability range is delineated by the upper and lower flammability limits. Outside this range of air/vapor mixtures, the mixture cannot be ignited at that temperature and pressure. The LFL decreases with increasing temperature; thus, a mixture that is below its LFL at a given temperature may be ignitable if heated sufficiently. For liquids, the LFL is typically close to the saturated vapor concentration at the

flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". The flash point is somet ...

, however, due to differences in the liquid properties, the relationship of LFL to flash point (which is also dependent on the test apparatus) is not fixed and some spread in the data usually exists. The

LFL_

of a mixture can be evaluated using the Le Chatelier mixing rule if the

LFL_

of the components

i

are known:Le Chatelier, H. Notes sur le dosage du grisou par les limites d’inflammabilité. Ann. Mines 388–395 (1891).

LFL_=\frac

Where

LFL_

is the lower flammability of the mixture,

LFL_

is the lower flammability of the

i

-th component of the mixture, and

x_

is the molar fraction of the

i

-th component of the mixture.

References

Chemical properties Fire {{Reaction-stub

See also

References