Highly flammable liquids
Highly flammable liquids (HFLs) should be treated carefully so
· They do not become a source of fire
· They do not fuel an existing fire
A 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 gives off 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:
ethanol +12 deg C
toluene +4 deg C
acetone -19 deg C
carbon disulphide -30 deg C
diethyl ether -45 deg C
As the flash points of all these liquids are below room temperature the liquids will always constitute a major fire and explosion hazard. The last three liquids have flash points below the temperatures which may be found in a refrigerator or freezer and will therefore constitute an explosion hazard even when in cold storage.
Bulk stocks
1) Bulk stocks of HFLs must be kept in the solvent store
2) Entry to the store should be restricted to authorised keyholders
3) Bottles of HFLs should be issued only to people with sealed bottle carriers capable of containing the contents of the bottle in event of spillage. The bottle carriers must be used to transport the HFLs to the laboratory.
Laboratory stocks
1) The total volume of HFLs in any laboratory or room in the department (other than the designated bulk solvent store) must be kept as low as possible and under no circumstances must it exceed 50 litres. (The 50 litre limit is set by legislation.)
2) All HFLs in a laboratory must be stored in specially designed and approved fire resisting cabinets. (Ordinary metal storage cabinets are not acceptable.) Cabinets should be located away from exits from the laboratory. Cabinets must be conspicuously marked with the approved labels to indicate that they contain HFLs. Cabinets should be used only for solvents and never for oxidants, acids, alkalis or other materials which could react with the solvents or cause corrosion of the cabinets. HFLs should not be stored on the open bench or in fume cupboards.
3) Bottles of HFLs temporarily removed from their storage cabinets should not be left on the open bench in direct sunlight. (Even in Aberdeen during the winter a relatively short period in sunlight can be enough to break a bottle through the build up of pressure caused by the heating effect of the sunlight.)
Refrigerator storage
1) If it is necessary to place HFLs in a refrigerator or freezer it is essential that a special refrigerator / freezer is used. It must be spark proofed and protected against an explosion. Even a very small amount of HFL in an ordinary refrigerator or freezer can create an explosive atmosphere which can then be ignited by a very low energy spark (e.g. from a thermostat). The consequences can be devastating. It is very likely that the resulting explosion will, at the very least, completely destroy the laboratory containing the refrigerator or freezer. Even in a protected refrigerator the HFLs must be kept in closed containers impervious to the solvent concerned. (Many plastics are not suitable.)
2) All refrigerators, freezers and cold rooms which are not spark proofed must be labelled with a sign indicating that they are not suitable for storage of any HFL (in either open or closed containers). Even if the flash point of the liquid is above that of the working temperature inside the refrigerator, storage is still not permitted. If the cooling system were to fail, the temperature could rise above the flash point and an explosive atmosphere could result.
Empty bottles
Empty bottles which once contained HFLs should be handled and stored as carefully as full bottles as they may contain explosive vapours.
Work with Highly Flammable Liquids
1) Those working with HFLs must be aware of the flash points of the liquids and must take care to exclude ignition sources from the work area. The risk assessment for the work must address how this will be done.
2) In deciding what might be a possible source of ignition, note must be taken of the autoignition temperature of the HFL. (The autoignition temperature is the minimum temperature required to initiate combustion.) It is not only sparks and naked flames which can be a source of ignition. If the vapour of the HFL comes into contact with a surface at a temperature in excess of the autoignition temperature, the vapour can ignite. The autoignition temperatures of two common solvents are:
carbon disulphide 100 deg C
diethyl ether 160 deg C
University of Aberdeen · King's College · Aberdeen AB24 3FX
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