Although most laboratory staff know that it is not safe to heat flammable liquids over an open flame there would appear to be a mistaken belief that an electric hot-plate is a satisfactory alternative.
It is recommended that the heating of highly flammable liquids should be carried out in such a way as to ensure that:-
- contact between the vapour-air mixture and the ignition source is avoided, eg by venting the system directly to open air or into the duct of a fume cupboard or by removing all electrical switches or controls, such as thermostats, from the immediate vicinity.
- heating sources are sufficiently cool so that ignition is not possible, eg by heating with steam or water baths.Highly flammable liquids with boiling points less than 80°C should be heated in this way.
Neither of these arrangements precludes the proper heating of reaction mixtures or carrying out distillations using properly installed electric mantles provided that there is adequate condensation or removal of any ignitable vapour.
- no unwanted highly flammable liquid is kept in the immediate work area.
Commonly used highly flammable liquids with flash points below 30°C:-
Acetone Hexane Benzene Methanol Butanol Methyl ethyl ketone Carbon disulphide* Pentane Cyclohexane Petroleum ether* Cyclohexene Propanol Dioxane Propyl ether Ethanol Pyridine Ethyl acetate Toluene Ethyl ether* Xylene
*Have ignition temperatures below 200°C