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Flammable liquids are among the most common hazards found in our industry.  This safety moment will focus on flammable liquids in the laboratory, which are usually significant in both variety and quantity.  The ability of a liquid to burn or explode varies depending upon characteristics inherent to that liquid. The flammability of a liquid depends upon the rate at which the liquid produces flammable vapors, which in turn is dependent on its vapor pressure. Vapor pressure increases with heat. Therefore, the warmer a substance is, the greater the risk of ignition. Of course, once a substance ignites, it will generate sufficient heat of its own accord to make this aspect self sustaining. The following are some of the properties of a flammable liquid that are inherent to its flammability.

Flash Point

This is defined as the lowest temperature, as determined by standard tests, at which a liquid gives off sufficient vapor to form an ignitable mixture with air near the surface of the liquid [within  the test vessel].  Among the most hazardous liquids are those having flash points at or lower than normal room temperature. These include most laboratory solvents, many petrochemicals, gasoline and most crude oils.

Auto-Ignition Temperature

This is the minimum temperature required to cause self-sustained combustion, independent of an ignition source. Laboratory personnel should be aware that there are substances used in a laboratory such as carbon disulfide or diethyl ether that have extremely low auto-ignition temperatures [80°C/176°F and 160°C/320°F respectively] and could be ignited by a steam line or a light bulb.  Also, some of the less exotic compounds can also reach auto-ignition temperature if left unattended on a hot plate or burner.

Flammable Range

Also known as "Explosive Limit”. For any flammable mixture there is a range of concentrations which can support combustion. This is known as the flammability range. The limits of this range are known as the Upper Flammable Limit [Upper Explosive Limit (UELV] and the Lower Flammable Limit [Lower Explosive Limit LELV]. Concentrations above the upper flammable limit are too rich to be ignited this happens when you "flood" the carburetor of a car. Concentrations that are below the lower flammable limit (LEL are too lean to burn - this happens if you cannot get enough gasoline to the carburetor of a car. The flammability range covers all concentrations between the upper and lower limits. This range becomes wider with increased temperature and in oxygen-rich atmospheres.

Ventilation is one of the most effective ways of preventing the formation of flammable mixtures. An exhaust hood should be used whenever appreciable quantities of flammable substances are transferred from one container to another, allowed to stand in open containers, heated or other such similar handling. This procedure prevents a substance from reaching its lower flammability limit.

Combustion

For a fire or explosion to occur, three distinct conditions must occur simultaneously:

  • A concentration of flammable vapor (FUEL).
  • An oxidizing atmosphere, usually air (OXYGEN).
  • A source of ignition (SPARK, FLAME, HEAT, ETC.).

Removal of any one of these three conditions will prevent the start of a fire (or extinguish an existing  one). As air exclusion is not a viable option, the problem usually resolves itself into maintaining a separation between flammable mixtures and ignition sources.

Control of Ignition Sources

Because spillage of flammable liquids is always a possibility, strict control of ignition sources is mandatory. There are many potential sources of ignition; some of the more common sources include:

  • Electrical Equipment
  • Electrical Plugs and Sockets
  • Static Electricity
  • Cigarettes, Cigarette Lighters and Matches
  • Bunsen Burners
  • Hot Plates and Mantles
  • Chemical Reactions
  • Steam Lines

The above is not a complete list. Anything that can cause a spark, flame or heat  generation is a potential ignition source.

When flammable materials are used in the laboratory, close attention must be given to ALL potential ignition sources, not just those in the immediate vicinity. The vapors of most flammable liquids are heavier than air and capable of traveling considerable distances. This possibility must be recognized and special note is to be taken of ignition sources at a lower level than that at which the substance is being used.

Flammable vapors from large sources such as spills have been known to descend into stairwells and elevator shafts and ignite on lower levels.  If the path of vapor within the flammable range is continuous, the flame will propagate itself back to the source.  Flammable substances should never be heated by using an open flame.  Preferred heating sources include steam baths, oil baths, heating mantles and hot air baths.

Storage in the Laboratory

The amount of flammable liquids in the laboratory at any one time is typically dependent upon the workload.  In a large or busy laboratory, the amount of this "work in progress" material can represent a significant volume of flammable material and one that frequently does NOT get a lot of attention. Everyone is busy going about their daily tasks and we tend not to notice how many samples are "building up." This can be problematic if appropriate attention is not paid.

  • Keep the amount of flammable liquids on hand to a minimum. When analyses are completed, transfer the remnants or retains to the sample store as soon as practical.
  • Ensure that there is adequate shelf storage for "work-in-progress" samples. Samples must not be stored on the floor or where they might block or restrict access to exits, safety showers, etc.
  • Samples should not be placed in areas where they might be subject to spillage or breakage - do not overload bench space or sample trolleys.
  • Where practical flammable samples should be separated from combustible samples. Petrochemicals must be segregated such that non-compatible types cannot come into contact with one another.
  • Local fire and building codes should be consulted as fire-proof cabinets may be required for short-term storage in the laboratory, depending upon the volume and container size of flammable material in use.

The following miscellaneous requirements and practices are also applicable:

  • Fire extinguishers of the correct type are to be strategically placed within the laboratory.
  • An adequate quantity of absorbent material, for the amount of flammables on hand, is to be readily available in case of a spill
  • Warning notices must be visibly posted where appropriate. The minimum requirements are:

Conclusion

Handling flammable liquids is a normal part of the everyday work activities for many of us and while the hazards are well known one of the greatest dangers is often that of complacency. Please remember that it can happen to you so you are the one who has to make sure that it does not happen. Look, observe, and be aware of what is going on around you.