Section: 16 | Types and Uses of Fire Extinguishers |

How to Cite this Reference

TYPES AND USES OF FIRE EXTINGUISHERS

Thomas J. Bruno and April A. Hill

The prevention and control of fires in chemical laboratories is extremely important to eliminate and minimize injuries, fatalities, and damage. This document discusses the different types of fire extinguishers and their proper use. See references for more details.

Typically, near the door or other means of egress of laboratories, one or more fire extinguishers will be suspended off the floor on a hook. The use of a fire extinguisher should NOT even be considered unless the following conditions are met:

An alarm has been issued by use of a pull station or other means to summon first responders
The laboratory room evacuation has been completed and verified by a head count
The fire is small, involving a single device or location, and is not spreading
The person considering use of a fire extinguisher is uninjured and is physically able to lift and aim the fire extinguisher (many are heavy and awkward)
The person considering the use of the fire extinguisher has a clear escape route and can avoid harmful fumes or smoke

Noted above is that the fire extinguishers are located near the door of the laboratory; this location is intentional. It is only after the evacuation is completed and emergency personnel notified that a person may look back into the laboratory from the door to determine if the use of a fire extinguisher is feasible.

Types of Fires

Type A: Fire involving general combustibles such as paper, wood, cloth, etc.
Type B: Fire involving solvents, flammable liquids such as gasoline, liquid and gaseous fuels, paints, etc.
Type C: Fire involving active electrical transmission lines, motors, wiring
Type D: Fire involving burning metals such as sodium, lithium, magnesium, metallic nanomaterials
Type K: Fire involving animal and vegetable fats in commercial cooking facilities

The most commonly encountered laboratory fires will be of the A, B, and C types, although with the exponential increase in research on nanoparticles, type D fires are more common.

Types of Fire Extinguishers

The types of fire extinguishers in use derive from the classification of the types of fires.

Pressurized water fire extinguishers can only be used on Type A fires involving paper, wood, or cloth. It is not likely that these fire extinguishers will be placed near laboratory doors, rather these are more often seen in office environments.

Carbon dioxide fire extinguishers can be used on Types B and C fires; they should not be used on fires involving paper because the release of the pressurized carbon dioxide can blow burning materials away from the source of the fire to surrounding areas.

Multipurpose dry chemical fire extinguishers, called ABC, can be used on fire types A, B, and C. The dry chemical in an ABC fire extinguisher is typically based on monoammonium phosphate (propelled with nitrogen gas), which, while not toxic, can be irritating. There is often a preference for the carbon dioxide fire extinguisher in the instrumentation laboratory because of the clean-up required (if not instrument damage) after the deployment of the ABC unit. An emergency is no time for hairsplitting; however, if an ABC is all that is available, use it.

Type D fire extinguishers use a special dry chemical based on graphite powder, sodium chloride, or copper that is used to absorb heat from a metal fire. Type D fires cannot be extinguished with any of the type A, B, or C units. It must be understood that Type D fires are extremely dangerous and difficult to handle in the best of circumstances. Indeed, a metal fire at sea is typically handled by pushing the burning object(s) overboard with a deck dozer. The fire extinguishers for Type D fires can never be used on any other type of fire. Laboratories that use metals, especially fine powders, should plan accordingly and ensure that a Type D fire extinguisher is available.

Type K fire extinguishers use a wet chemical, or chemical foam compounds and are rarely needed in chemical laboratories. Type K fires usually occur in commercial kitchens, though food chemistry laboratories should be aware of the hazard. As with Type D fires, use of other types of fire extinguishers will only make things worse.

Using Fire Extinguishers

Operation of the fire extinguisher is depicted in the figure below showing the PASS method, as outlined below.

Pull the pin

Aim the hose or nozzle at the base of the fire

Squeeze the trigger

Sweep side to side until all signs of the fire have been extinguished

Once a fire extinguisher is deployed, it must be removed from service and refilled or replaced, not returned to the wall hook.

Every person working in a chemical laboratory, even occasionally or infrequently, should be trained in using fire extinguishers correctly, including hands-on use for all types of fires that may be encountered. Such training should be on an annual basis.

References

Bruno, T. J., Robinson, J. W., Slelly-Frame, E., and Frame, G. Undergraduate Instrumental Analysis, Eighth Edition, CRC Press/Taylor & Francis, Boca Raton, FL, in preparation.
NFPA 10 - Standard for Portable Fire Extinguishers, NFPA, Quincy, MA. <www.nfpa.com>

FIGURE 1. The PASS method of operating a fire extinguisher. Reproduced with permission of the National Fire Prevention Association (NFPA).

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