edlted by MALCOLM M. RENFREW University of ldaho Moscow, ldaho 83843
Fire Safety and Fire Control in the Chemistry Laboratory A. C. Wilbraham Southern lllinois University Edwardsville, IL 62026
The potential for a fire in the chemistry laboratory i s high, but the majority of fires can be prevented if precautionary measures are tnken. or if fire safetv attitudes are es-
to take to prevent fires and the actions that should be taken if a fire occurs. The control of a small fire prevents a larger fire from becoming a reality. In the event of a fire, decisions must he made quickly. A person who has received some basic training in fire safety and fire control and, most importantly, has had hands-on experience in fighting a fire is more likely to react rationally and in the best interests of safety when confronted with a real fire. Such a person will make decisions with mod iudernent and without emotion. Toex-
Fire is the result of the combustion process. If one or more of the components of the fire triangle can be eliminated, the combustion process ceases, and the fire is extinguished. A fourth component of any eombustion process, not shown by the fire triangle, is the existence of a suitable reaction pathway. Classification
of F i r e s
Fires are classified, in general, on the basis of the fuel component characteristics. There are four classifications.
I
ORDINARY
I
IBI COMBUSTIBLES
Class A: Fires involving ordinaxy combustible material such as paper, wood, fabrics, plastics, and rubber.
The C o m b u s t i o n Process Combustion is s chemical reaction in which a fuel is oxidized and heat is liberated. The process involves three components: (1) a fuel-material to bum, such as wood or gasoline. (2) an oxidizer-a substance to support combustion, far example, oxygen and chlorine. (3) an ignition source--to initiate the combustion process, such as a spark, a flame, or heat.
Class B: Fires involving flammable liquids, gases, greases, paints, solvents. and eookine oils.
The relationship between the components of the eombustion process are conveniently presented in the fire triangle.
Class C: These are Class A ar Class B fires which also involve energized electrical equipment, power panels, hot plates, and electrical appliances.
ELECTRICAL
EQUIPMENT
El COMBU TlBLE
FIRE TRIANGLE
Class D: Fires involving combustible metals such as magnesium, sodium, and potassium. (Continued on page A3121 Volume 56, Number 10, October 1979 1 A311
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Characteristics of the Combustion Process Ordinary combustible materials decompose when heated producing volatile gases. If the temperature is high enough, these gases can ignite togive visible evidence of a fxe, i.e., flames. As the gases burn more heat is generated, and the fuel mass gets hotter. The rate of volatile gas evolution increases and so does the size of the fire. This is a Class A fire. When the vapor of a flammable liquid is mixed with air and ignited the result is often explosive. There is a rapid generation of heat and an increased rate of vaporization of the liquid-the fire spreads rapidly. This is a Class B fire. The combustion process for both Class A and Class B fires involves a chain-reaction ~athwav.The heat of the reaction causes the tuel co&tponents to break into fragments called radicals. These radicals or chemical intermediates are very reactive species and comhine rapidly with an oxidizer, usually oxygen, releasing heat and light and forming a variety of combustion products.
The Theory of Extinguishing a Fire If one or more of the components required for combustion is eliminated, the fire will he extinguished. This is the theoretical basisof firefighting. The success of extinguishing a fire depends inlarge part upon the speed with which this elimination process can be performed. (1) Removal of fuel: This is usuallv difficult to do, but in some situations it might be pokible, a valve may be turned to cut off the fuel supply. (2) Removal of oxidizer: The oxidizer is usually oxygen from the surrounding air. Oxygen can be excluded by covering the fire with an inert substance, by spraying it with water or a dense inert gas Such as carbon dioxide, or by means of a fire blanket. Dilution of the oxygen in the air surrounding a fire is an effective means of reducing the combustion process. (3) Removal of source of ignition: This is of little mnseauence after a tire bas started, but keeping an ignition source away from combustible materials is a positive way to prevent a fire from wcurring. (4) Inactivation of ehemical intermediates: The rornhurtion process ran be reduced rapidly by spraying the lire with substanre that inactivate the reaction interrn~diales.These wbstances are known a- radirnl traps. As thr combustion rate drcrewes, heat e\,olution stops, and the fire goes out. ~
~~
Characteristics ofSpecific Extinguishing Agents The extinguishing agents in most mmmon use are water, inert gases, chemical powders, and halons. A312 / Journal of Chemical Education
(1) Water Water can he used for Class A fires as an effective extinguishing agent because (a) it has a very high heat capacity and cools the fuel as it removes heat, and (b) it dilutes the oxygen content of the atmosphere surrounding the fire as it is converted into steam. There is a volume increase of nearly two thousand-fold during this process. T o he most effective water must be used as a fine spray. Water has several disadvantages as an extinguishing agent. I t has a high freezing point, which prevents its use below O'C, a high surface tension, which leads to a high degree of "run-off," and alow viscosity, which prevents it from sticking to vertical surfaces. These disadvantages are overcome to some extent by adding calcium chloride to lower the freezing point, detergents or surfactants to lower the surface tension, and thickening agents, such as silicates and phosphates or organic polymers to increase the viscosity. Since the water in a water extinguisher contains dissolved salts it must never be used on Class C fires! (2) Compressed Gases Inert gases can be used to dilute the concentration of oxygen in the atmosphere surrounding Class B or Class C fires below that required for combustion. The most commonly used gas is carbon dioxide hecsuse (a) it is clean in operation and leaves no residue (b) it can be used on or around energized electrical equipment (e) the fill gas is readily available and inexpensive (d) it can he discharged under its own vapor pressure (e) the gas has a slight moling effect on the sprayed area. Carbon dioxide has several disadvantages. The gas has poor extinguishing efficiency and is required in high concentration. It is also an asphyxiant. This makes it undesirable for use in occupied areas which have limited access and poor air circulation. (3) Dry Chemical Powders Chemical compounds such as sodium bicarbonate, potassium bicarbonate, ammonium sulfate, potassium sulfate, potassium chloride, and ammonium pbosphate in dry finely-powdered form are widely used as extinguishing agents. Dry chemical powders quench flames almost instantaneously. The rapid effect is due to inhibition of the ehemical chain reaction. The radicals, atomic and molecular fragments produced during comhustion of a fuel, are "trapped" by the constituents of the dry chemical powder, the chain reaction is terminated, and the fire is extinguished. Dry chemicals are excellent fire extinguishers, but they do not lower the temperature of the environment. Another agent, usually water, is used to cool the area below the ignition temperature after the flames have been extinguished. Dry chemical powder extinguishers containing sodium or potassium carbonate are suitable for Class B and Class C fires. They are particularly effective for fires involving burning oils or fats because they cause saponification to occur
on the liquid surface which helps t o prevent reignition. These eatinguishers are not recommended for Class A fires. Monoammonium phosphate (MAP) is the agent used in the portable dry powder extinguishers found in the home or car. MAP extinguishers are suitable for Class A, B, and C fires. MAP does not cause saponification of oils or fats, hut it is an effective extinguishing agent. When this agent is heated i t decomposes and leaves a molten residue adhering to hot surfaces, oxygen isexcluded, and the firecannot be propagated. (4) Holons Halons are halogen substituted methanes. They are more dense than air. Examples include hromochlorodifluoramethane (CFsBrCL), a liquid, and hromotrifluoromethane (CF3Br), a gas. Both of these compounds are thermally unstable and break down to form radicals a t moderate temperatures. CF3Br
-
CF3.
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(1) Portable Stored-Pressure Extinguishers. In these devices the expellent gas and the extinguishing agent are hoth together in a single container. Discharge of the contents is controlled directly by a lever-operated valve. The condition of extinguishers of this type can easily be determined since they are usually equipped with a pressure gauge.
Ring pin
Operating level Pressure gauge Expellent gas
+ BP
The chemical intermediates, formed in any class of fire, are trapped by the halon radicals causing the combustion process to cease. All halons and their by-productsare toxic exceot the fullv fluorinated comoound tetmfl;mromethak CFaL .~ -. This substance is very stable thermally and is ineffective as a chain reactiun stopper, but i t may put out fires by smothering them. Halons are clean and safe if used with appropriate precautions. Automatic fire extinguishing systems (sprinklers) that protect sensitive electronic equipment, such as computers, are often charged with halons. ~
Two hapic types of hand-portahle extinguishers are available (11 stored-prwure and ( 2 ) cartridge operated.
Discharge tube Water
~
Extinguishing Equipment In Nearly All Cases of Fire TIME IS AN ESSENTIAL FACTOR-Every Second Saved is Important. YOU CANNOT AFFORD TO WASTE TIME LEARNING HOW T O OPERATE AVAILABLE
(1) Pressure Vessel-usually made of steel or aluminum and designed to withstand a pressure of a t least four times the normal operating conditions. (2) Control Value or Leoer-to provide the operator with a means for controlling the discharge of the extinguishing agent. (3) Pressurizing Gns-dry chemical powder and water extinguishers require the w e of an inen expellent airs Wrh as COX.These extinguishers have #,per. ntme ilrrbsures ot 150 200 ~ I R . "
Nozzle
Figure 1. Water extinguisher.
(a) WnterExtinguisher The water extinguisher (Fig. 1) is only suitable for Class A fires. Their capacity is usually 2.5 gallons, and calcium chloride is often added t o prevent the contents from freezing when the air temperature drops below 0%. To operate, pull out the ring pin, grasp the nozzle, and squeeze the operating lever. The stream of water should be aimed directly onto the burning material. The horizontal range of the jet water is 30-40 feet and the discharge rate is approximately 1gallon per 15 sec.
/Ring
pin
"
dioxide, and dry chemical powders are the three most common agents.
Hand-Portable Extinguishers The total weight of a portahle extinguisher is usually less than 55 lb; the weight of the contents may vary from 1-30 lb. An extinguisher should he carried close to the fire before being activated, and after use any remaining pressure should he relieved. The use ofany fire extinguisher should be reported to the safety officer as soon as possible so that the equipment can be replaced or recharged.
Figure 2. Dry chemical powder extinguisher.
(Continued on page A314) Volume 56, Number ID, October 1979 1 A313
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Opcmting lever
Nozzle
.
,Rang
pm
Puncture lever
(2) Dry Chemical Powder Eztinguisher C 4 cortr~dge
Extinguishers of this type (Fig. 2) may he rated for Class A, B, or C fires, depending upon the agent used. They are available in various sizes from 1-30 lh and are usually placed in 1ocations.where high use factors are not encountered such as the car and home. To operate, pull out the ring pin, remove the hose from the holder, and squeeze the operating lever. Dry chemical powder is forced up the discharge tube, through the hose, and out of the nozzle. Direct the powder stream at the base of the flame in a side,-tu-side saveplng mwement. The horimntal mnce 1s i - 2 U feet, and thr discharge rnte IS 3 h u t 1 II) 3ec.
Gar
tube
Chemical
powder *outlet
elbow
Figure 4. Portable, eamidg~perated,dv chemical powder extinguisher.
These extinrmishers (Fie. ,. 4). can be rated ibr ('lass A, ti.?, or 1) l&sdependmg upon the nmtrnti They are avndnhlc in 5-11, :III-II, size3 and are urunlly Imntrd in high use areas. T o operate, remove the ring pin and hose. Push down hard on the puncture lever to release expellent gas from the cartridge into the dry chemical eompartment. Squeeze the nozzle operating lever and direct a stream of powder s t the base of the flame using a side-to-side motion. The horizontal range is 5-20 ft and the discharge rate is 1ihlsec.
Extinguisher Ratings
Figure 3.Carbon dioxide extinguisher
(c) Carbon Dioxide Extinguishers
This type of eatinguisher (Fig. 3) is suitable for Class B and C fires and is available in 2 lh-25 lb sizes. COz extinguishers are stored-pressure devices in which the expellent gas is also the extinguishing agent. To operate, pull out the ring pin and remove the horn from the holder. B E SURE TOHOLDTHEINSULATEDHAND G R I P BECAUSE T H E DISCHARGE
the hose and out of the discharge horn as agas. Direct theconstream a t the baseof the flames using a side-ta-side sweeping movement. The range of this type of extinguisher is only 3-8 ft and the discharge rate is 1 lblsee. (2) Portable Cortridge-Operated Extinguishers In this type of extinguisher the expellent gas is stored in a separate container from the extinguishing agent. The extinguisher is activated by releasing the expellent gas into the main chamber which contains the extinguishing agent; discharge is controlled hy a valve a t the end of the discharge hose. The condition of these extinguishers is checked by weighing. A314 / Journal of Chemical Education
The Underwriters Laboratory UL rating on the eatinguisher label gives the type and relative size of fires theextinguisher can put out. Inspect the labels on the extinguishers in your facility. The information enables you to choose the correct extinguisher for the job. The class of fire against which a particular extinguisher is effective is indicated by the designations A, B, C, or D or any combination of these. Class A rating: The numerical rating assigned by the Underwriters Laboratories indicates the relative effectiveness of the extinguisher. A fire rated l-A can he extinguished by 1% gallons of water, hut a 2-A fire requires 2% gallons of water. A 2-A unit is twice as effective against a Class A fire as a l-A unit. A fire rated 8-A requires one 8-A or four 2-A rated eatinguishers.
the extinguishing agent will not conduct electricity. The rating number 10 indicates the relative size of the Class B fire the extinguisher will put out-approximately 10 square feet of fire area. It should he noted that B:C rated extinguishers are not effective on C l a s A tires such a i lmrning wot,d, paper, o r plastic. The rnnyeof n I O - R : C r r t ~ n m ~ ~ h c r i - n h u t I:, tcst.and the disc harce timeis ltr sec.
An extinguisher rated l-A; 10-B:C has the same rated effectiveness on flammable liquids as a 10-B:C extinguisher, hut i t is also rated to put out Class A fires. An extinguisher of this type is particularly valuable in residential fires in which ordinary combustibles (Class A) are usually ignited and live electrical equipment (Class C) is often involved. The "1" before the A rating indicates the relative size of that class of the fire the 1-A, 10-B:C unit will put out. The range is about 13 f t and the discharge time is 10 sec. This extinguisher is about half as effective as the large pressurized water units (rated 2-A) commonly found in schools and offices. A 2-A; 40-B:C extinguisher is twice as effective for Class A fires and 4 times as effeetive for Class B and Class C fires as a L A ; IO-B:C rated unit.
An Exercise Program in Fire Control No introductory fire training program can effectively cover all needs because every accupation has particular fire risks associated with it which require special consideration. There are, however, basic procedures to be followed in fighting a fire. It is recommended that chemistry students he given hands-on experience with fire extinguishers as described in "A Firefighting Experience as a Laboratory Experiment," JOURNAL OF CHEMICAL EDUCATION, 55, A405, Navemher 1978.
Extinguisher Maintenance and Location It is imperative that firefighting equipment he checked periodically. Any use of equipment should be reported as soon as possible. Equipment failures are usually the result of neglect; extinguishers will not operate unless charged and maintained regularly. A used extinguisher should never be returned t o its holder. I t should he replaced with a new extinguisher o r recharged a s soon a s possible after use. Although you may not he personally responsible, you should understand that an improperly serviced eatinguisher can he dangerous and may fail t o work when vou need to use it.
Class B rating: The B rating number of an eatinguisher designates the area of a contained gasoline fire (in square feet of fire area) that a nonexpert operator can expect to extinguish. Using a 40-B rated extinguisher, the nonexpert can he expected to control a fire area of 40 square feet. Combination ratings: An extinguisher rated 10-B:C is effective an Class B fires, involving flammable liquids or greases, and it also is safe to use when the fire involves live electrical equipment because
HOW TO USE THEM. Bnrw requirementr regarding location and maintenance ul iire extitlgu:~h~rs: 1) Fire extinguishers should he maintained in proper working condition and checked on a regular basis. 2) A used extinguisher should never he returned to its holder. I t should he replaced or recharged as soon as possible. 3) All extinguishers should be clearly marked as t o class and use.
4) Locations of extinguishers should be clearly indicated. 5) An extinguisher should be located in a convenient place, a t a convenient height, carefully mounted on a bracket, and kept readily accessible a t all times. Extinguishers should not be used as coat hangers!!!
Fire Safety Procedures and Practices Fire prevention measures start with the facilities. The ideal facilities are of fireproof construction with easy opening, self-closing doors that provide isolated storage for flammables. Automatic smoke and fire detectors and control devices should also be installed. In Case of a Fire Act Quickly But Calmly Before a fire occurs you should know: 1) The location, type, and operation of available firefighting equipment. 2) The location and operation of safety showers and eyewash stations. 3) The location of exits from the room or laboratory. 4) The location of the safety phone or other alarm systems such as a pull station. 5) The emergency procedures to fallow
Preventive measures-safety practices to adoot: i) Limit the volume of flammable liquids in the laboratory. (The maximum
volumes of flammable solvents allowed in the laboratory are specified in OSHA regulations.) 2) Always store flammable liquids in safety cans if possible. 3) Keep flammables, corrosives, and toxicants separated in storage. 4) Wear tight-fitting sleeves and confine loose hair when working with or near open flames. 5) Wear protective clothing and safety goggles. 6) Do no smoke in the laboratory or when handling flammable materials. 7) Never work alone in the laboratory. 8) Keep all doors closed. 9) Do not block exits. 10) Keep fire extinguishers readily accessible.
Accidents Do Happen Even if you are careful and take precaution. ary measures you may still have a fire. In case of fire: 1 ) DO give the alarm, call for help, give your name and location of fire. DO NOT HESITATE TO GIVE T H E ALARM. 2) DO keep windows and doors closed to stop fire and smoke from advancing. DO NOT open a door if it feels hot. 3) DO keep calm. DO NOT panic. 4) DO attempt to extinguish the fire, if it is small, using the proper extinguisher. DO NOT try to extinguish a fire if you do not have the proper equipment or
if it is too large. Leave the area immediately. 5) DO drop to the ground and roll over to smother flames if your clothing is on fire. Someone should wrap you in a coat or fire blanket if possible. DO use a safety shower if you are close to it. DO NOT run. Running fans the fire. 6) DO crawl along the floor and breathe through a wet handkerchief, taking short breaths, if caught in a fire and smoke conditions are had. DO NOT stand up. 7) DO proceed to nearest exit or evacuation area using stairwells if evacuation is necessary. DO NOT use elevators, remain in exit paths, or return ta fire location. 8) DO, if time permits, turn off all utilities such as gas, electric, but DO NOT if it imposes a risk. 9) DO report all fires no matter how small. DO NOT forget! 10) DO inform the safety officer of any fm extinguisher used so it can be replaced or refilled. DO NOT leave it for someone else to discover that an extinguisher is empty when an emergency exists. Fire safety is the responsibility of everyone. Good safety attitudes and an effective training program will minimize the risks and
Acknowledgement Illustrations courtesy of the Ansul Company
Volume 56, Number 10, October 1979 / A315
