Polycarbonate is much stronger and self-extinguishing after ignition but is readily attacked by organic solvents.
All chemical laboratories should have carbon dioxide and dry chemical fire extinguishers. Other types of extinguishers should be available if required for the work being done. The four types of extinguishers most commonly used are classified by the type of fire for which they are suitable, as listed below. It should be noted that multipurpose class A, B, and C extinguishers are available.
Water extinguishers are effective against burning paper and trash (class A fires). These should not be used for extinguishing electrical, liquid, or metal fires.
Carbon dioxide extinguishers are effective against burning liquids, such as hydrocarbons or paint, and electrical fires (class B and C fires). They are recommended for fires involving computer equipment, delicate instruments, and optical systems because they do not damage such equipment. They are less effective against paper and trash fires and must not be used against metal hydride or metal fires. Care must be taken in using these extinguishers, because the force of the compressed gas can spread burning combustibles such as papers and can tip over containers of flammable liquids.
Dry powder extinguishers, which contain ammonium phosphate or sodium bicarbonate, are effective against burning liquids and electrical fires (class B and C fires). They are less effective against paper and trash or metal fires. They are not recommended for fires involving delicate instruments or optical systems because of the cleanup problem. Computer equipment may need to be replaced if exposed to sufficient amounts of the dry powders. These extinguishers are generally used where large quantities of solvent may be present.
Met-L-X® extinguishers and others that have special granular formulations are effective against burning metal (class D fires). Included in this category are fires involving magnesium, lithium, sodium, and potassium; alloys of reactive metals; and metal hydrides, metal alkyls, and other organometallics. These extinguishers are less effective against paper and trash, liquid, or electrical fires.
Every extinguisher should carry a label indicating what class or classes of fires it is effective against and the date last inspected. There are a number of other, more specialized types of extinguishers available for unusual fire hazard situations. Each laboratory worker should be responsible for knowing the location, operation, and limitations of the fire extinguishers in the work area. It is the responsibility of the laboratory supervisor to ensure that all workers are shown the locations of fire extinguishers and are trained in their use. After use, an extinguisher should be recharged or replaced by designated personnel.
Heat sensors and/or smoke detectors may be part of the building safety equipment. If designed into the fire alarm system, they may automatically sound an alarm and call the fire department, they may trigger an automatic extinguishing system, or they may only serve as a local alarm. Because laboratory operations may generate heat or vapors, the type and location of the detectors must be carefully evaluated in order to avoid frequent false alarms.
Fire hoses are intended for use by trained firefighters against fires too large to be handled by extinguishers and are included as safety equipment in some structures. Water has a cooling action and is effective against fires involving paper, wood, rags, trash, and such (class A fires). Water should not be used directly on fires that involve live electrical equipment (class C fires) or chemicals such as alkali metals, metal hydrides, and metal alkyls that react vigorously with it (class D fires).
Streams of water should not be used against fires that involve oils or other water-insoluble flammable liquids (class B fires). Water will not readily extinguish such fires. Rather, it can cause the fire to spread or float to adjacent areas. These possibilities are minimized by the use of a water fog. Water fogs are used extensively by the petroleum industry because of their fire-controlling and extinguishing properties. A fog can be used safely and effectively against fires that involve oil products, as well as those involving wood, rags, rubbish, and such.
Because of the potential risks involved in using water around chemicals, laboratory workers should refrain from using fire hoses except in extreme emergencies. Otherwise, such use should be reserved for trained firefighters. Clothing fires can be extinguished by immediately dropping to the floor and rolling; how-