2.2.6 Flammable Solvents

2.2.6 Flammable Solvents


Solvent supplies in laboratories should be kept to a minimum, preferably not more than will be needed during the working day. Solvents must be returned to flame-proof cupboards when not in use. Ether is especially dangerous because of its flammability.


Not all concentrations of a flammable vapour in air are flammable . For each vapour, there is a concentration below which and above which propagation of a flame will not occur. These are known as the lower and upper explosive limits, and vary widely for different substances, e.g.:-

Hydrogen -  4% - 74%

Carbon Monoxide - 12.5% - 74%

Carbon Disulphide - 1% - 50% (the autoignition temp is 90°C - about the same temp as a cup of hot tea!)

Benzene - 1.% - 8%

"Many common solvents have a flammable range of about 1% to 10% and so would appear to be safer than those substances with a wide flammable range. This is only partially true, however, as most of these solvents give concentrations of vapour in the flammable range at room temperature.

The most useful parameter of flammability is the "flashpoint". This is the lowest temperature at which a vapour-air mixture will ignite, if an ignition source is introduced. Some solvents such as diethyl ether and carbon disulphide are so flammable that they have flashpoints below 0 degrees Celsius, eg, at -45 °C enough diethyl ether will evaporate to be ignitable. (This is the reason why it is so dangerous to store flammable solvents in a domestic, ie, non-spark proof, refrigerator). Most of the common organic solvents have flashpoints at or below room temperature and are thus a significant fire hazard.

The auto-ignition temperature is the lowest temperature at which a substance (solid, liquid or gas) will self-ignite and sustain combustion in the absence of a spark or flame. For solids, this value is greatly influenced by the size, shape and rate of heating."

[Extract of Safety Handbook, Safety and Environmental Protection Services, (SEPS) 'Hazards of Dangerous Chemicals' - http://www.gla.ac.uk/services/seps/publications/safetyhandbook/chemicals.html]