Extinguishing fires with chemicals - ACS Publications - American

EXTINGUISHING FIRES WITH CHEMICALS*

Data are given for the losses of human life and of property in the United States which are caused by fire. A study is made of the most important chemicals that are being used for extinguishingfires. I n connection with these chemicals, the warious types o f extinguishers which are employed for the extinguishment of fires are disrussed. A little fire i s quickly trodden out: Which, being suffer'd, rivers cannot quench. SAAKESPEARE, Third part of Henry VI, Act IV, Scene VIlI

A Few Figures The majority of people concern themselves very little with fires and imagine that most fires take place in factories. However, this is not the

case. Factories are generally better protected against fires than are private homes. More than 60% of all fires in the United States (costing the people over $500,000,000 a yearj occur, not in factories, garages, or public buildings, but in the "safe" home. Every "average" day of the year we burn 1127 homes, 10 public buildings (including 5 schools), 5 churches, 1.5 hotels, 1 hospital, 4 warehouses, 114 farm buildings, 3 wood-working plants, 5 metal-working plants, 7 clothing factories, 6 department stores, 2 theaters, 8

* Presented st the joint intersectional meeting of the American Chemical Society and of the American Association for the Advancement of Science at Syracuse, N. Y., June 25, 1932. 1503

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public garages, 3 printing plants, 3 drygoods stores, and 6 food and food productsfactories. The most amazing figure is the large number of home fires: 1127 homes every day! That means one home fire for each four minutes of the day. Approximately 5000 children are killed every year in these fires that destroy our homes, while the total yearly loss by fire is about 10,000 lives. Ten thousand people every year! This is the population of a city the size of Herkimer, New York. I t is an astonishing fact that in spite of these tremendous annual losses, relatively few homes, factories, and other buildings are properly protected against fires. The reason for this paper is to show the importance of choosing carefully the proper fire-fighting equipment for a given fire hazard. Fire Extinguishers and Chemicals Figure 1shows a picture of a 6re which is being put out by one of the first fire extinguishers ever made. The picture was taken from a small booklet entitled: "Letter addressed to Sir John Sinclair, Bart., President of the Board of Agriculture and Improvement. Respecting the Internal Discovery Lately made in Sweden, of a Method to Extinguish Fire, with an Account of the Process adopted for that Purpose; and Hints of means for Preserving Timber Used Either in Houses or in Ship Building, from that Destructive Element, by Mr. William Knox, Merchant in Gothenburg." This 32-page booklet is "A treatise on the constituent principles of various simple and compound solutions for extinguishing fire; sent to the Royal Society of Arts and Sciences a t StockQ,olm, 13, Dec. 1792. By Nils Nystrom, Apothecary in Norrkoping. Translated from the original Swedish, 13, Nov. 1793." The Swedish inventor recommended the following solutions to be mixed with water in the proportions given, and expelled from hand-operated engines. 1. 2. 3. 4.

5. 6. 7.

1.

Simple Solutions 12 kans of the strongest solutions of wood ashes, to 100 kans water. 8 kans of the h e s t heat pot ashes, to 100 kans water. 10 kaus of well dried and fine beat kitchen or common salt to 100 kans water. 10 kans of well dried and fine beat vitriol or copperas, to 100 kans water. 15 kans of the strongest herring pickle, to 100 kans water. 12 kans of fine heat alum, to 100 kans water. 20 kans of well dried, fine beat, and well sifted clay to 100 kans water. Compound Solutions 10 kans of a compound of clay, vitriol, and common salt, say 3'/., kans of each, to 100 kans water.

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2.

12 kans of the strongest solution of wood ashes, and fine clay reduced to a powder, say 6 kans of each, to 100 kans water. 3. 10 kans of a compound of red ochre, or the residuum of aquafortis, and common salt, say 5 kans of each, to 100 kans water. 4. 10 kans of a compound of the strongest herring pickle, and red ochre, or the residuum of aquafortis, say 5 kans of each to 10 kans water.

It was back in the prehistoric era that man believed that water could be used to extinguish all fires. This is no longer pniversally true today in our complex civilization. Water can still be employed to extinguish many fires, but it is worse than useless, even dangerous, to employ i t on others. That the Swedish inventor, back in 1792, used a number of chemicals other than water is shown by his formulas. This was less than 140 years ago. In this interval of time a large amount of research has been done in this field. New chemicals have been tested and are still being tested for their fireextinguishing power. Only recently, the United States Bureau of Mines published a report on the extinction of methane flames by dichlorodifluoromethane (1). Not only new chemicals but also new types of fire-fighting apparatus have been developed during these 140 years. It is obvious that not all of the fire-fighting apparatus which is on the market today is of the same quality, some of it being rather inefficient. The highest types of fire extinguishers made in this country and Canada are approved and regularly inspected by either one or both of the following organizations: The Factory Mutual Laboratories or the National Board of Fire Underwriters' Laboratories. The Factory Mutual Laboratories were established in 1890 and are under the direction of the Associated Factory Mutual Fire Insurance Companies.

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The Underwriters' Laboratories (Incorporated 1901) were established and are being maintained by the National Board of Fire Underwriters. The approval insignia on the fire extinguishers approved by the Factory Mutual Laboratories is a small diamond-shaped mark containing the capital letters FM and is stamped on the nameplate of the extinguisher. The approval label of the Underwriters' Laboratories is much larger and is rectangular in shape. It is made from embossed or etched brass (Figure 3). The label gives, first, the heading: Underwriters' Laboratories, and below this heading is the word: "Inspected." Then follows a brief statement describing the type of extinguisher for which this label was issued, e. R. "One Quart Hand Fire Extinguisher," "Fire Extinguisher on Wheels," "5 Gallon Fire Extinguisher," etc. Below this statement the t v ~ of e fire is indicated for which this extinguisher is intended and also the actualnumber of the extinguishers necessary. It is customary to distinguish between three classes of fires: Class A, B, or C. According to the Underwriters', "Class A fires are defined as incipient fires on which the quenching and cooling effectsof quantities of water are of first importance, i.e., incipient fires in ordinary combustible materials, such as wood, paF ~ c u n ~:~.-SUME r TYPICAT. APPROVAL LABELSOF per, textiles, rubbish, etc. THE UNDERWRITERS' LABORATORIES Class B fires are defined as incipient fires where the blanketing or smothering effects of the extingu:sl~ ing agent are of first importance, i. e., fires in small quantities of rap:dly burning material, such as gasoline, oils, or greases in vats or other open vessels or on floors. Class C fires are defined as incipient fires in electrical equipment where the use of a non-conducting extinguishing medium is of great importance." Thus the classification letter A, B, or C indicates the type of fire for which any particular extinguisher was designed and is best suited. The various types of fires extinguishers differ in their efficiency, i. e., extinguishing value. Hence it was found necessary to group together one to five appliances as a unit of first-aid fire protection. The actual number of extinguishers necessary for such a unit of first-aid hand fire protection is indicated by the number 1 to 5 following thr classification ,A

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letter A, B, or C. Both laboratories publish semi-annually a list of approved and inspected fire-protection appliances. These lists cover not only extinguishers, but all kinds of appliances that deal with fires, e. f., electrical alarms, hydrants, sprinklers, waste cans, etc.* The various types of fire extinguishers have been especially designed by the manufacturers of fire appliances because no one extinguisher is satisfactory for all fires, for, contrary to common belief, fires are not all alike. One type of extinguisher is excellent for one type of fire but not a t all suited for another fire risk. Furthermore, it is necessary to make the various types of extinguishers in various sizesin order to suit the proper conditions. A Class A fire calls for an extinguishing device of the cooling or quenching type. This type includes such devices as soda and acid extinguishers, fire pails, bucket tanks, etc. Such extinguishers containing water or water solution are used where a cooling effect or wetting do& is required. They cool the burning material (wood, rubbish, fabrics, paper, textiles, etc.) below the kindling point. A class B fire (gasoline, oil, grease, etc.) requires an extinguisher of the blanketing type. Such a fire cannot always be extinguished with a Class A extinguisher. Should such an extinguisher be used, the fire might spread and not be extinguished; the water or water solution having a greater density than that of the material, the vapors of which are burning, would sink below the level of the liquid and cause it to o v d o w the container and spread. The Class B type extinguishers include the foam, carbon tetrachloride, and carbon dioxide types. A Class C fire is propagated in electrical equipment, such a$ panel boards, switch boards, household appliances, and electrical equipmen* in general. Hence the attempt should not be made to extinguish it with a chemical that conducts the electrical current. Carbon tetrachloride or compressed carbon dioxide (from a carbon dioxide cylinder and not from a soda and acid extinguisher) should be used. It is of the utmost importance that extinguishers of all types should be kept filled at all times and recharged a t once after use. They should be inspected periodically to guard against tampering: they should be discharged and refilled annually to insure satisfactory operation in an emergency. Water as an Extinguishing Liquid There is no mechanical extinguisher built a t the present time which employs water only as a fire-extinguishing agent, except the one using a manually operated pump contained in a receptacle holding water. An-

* The lists can be obtained free of charge by writing to the following addresses: Underwriters' Laboratories, Inc., 270 East Ohio Street, Chicago, Ill.; 109 Leonard Street, New York City; or 615 Commercial Street. San Francisco, Cal. Associated Factory Mutual Fire Insurance Companies, 184 High Street, Boston, Mass.

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other fire-aid appliance which sometimes contains nothing but water is the standard fire pail having a capacity of 12 quarts. In many cases, however, these pails contain not water only, but an aqueous solution of a chemical freezing-point depressant such as calcium chloride; this is also true of the above-mentioned pump type extinguisher. Such solutions are used wherever the storage temperature falls below the freezing point of water. The concentration of solutions using temperature depressants to reduce the freezing point depends on the lowest temperature which may be encountered. For instance, a solution containing 7 lb. 6 oz. of 75% calcium chloride in two gallons of water has a freezing point of - 10°F. (-23.33°C.), while a solution containing 10 lb. of 75% calcium chloride in the same volume of water freezes a t -40°F. (-40°C.). The strength of the solution can be checked easily by determining its specific gravity. Thus the specific gravity of the first solution m.entioned is 1.205, while that of the second one is 1.263. The calcium chloride used in making up these solutions must be free from magnesium chloride as the latter compound promotes corrosion. The approved pails are round-bottomed and made of galvanized iron, steel, or fiber. They are equipped with a loosely fitting cover. At the inception of a fire of the Class A type (wood, paper, textile, rubbish, etc.) the contents of the pails are thrown or poured over the whole surface of the ignited mass. Thus the quenching and cooling effect of the water, or of the anti-freezing solution of calcium chloride in water is utilized. Sometimes a number of these pails are nested together in a cylindrical steel tank which is filled with water qr the anti-freezing solution. The capacity of these tanks varies from 22 to 32 gallons. They can be closed tightly; hence very little evaporation occurs. Of course, water is still used in most sprinklers and fire engines. During the last few years a number of pipe-line installations have been put on the market which are not equipped with water, but which contain chemicals, such as carbon dioxide, foam solutions, or carbon tetrachloride type fireextinguishing liquids. Dry Carbon Dioxide Gaseous carbon dioxide bas a density of 1.53 as compared with air having a density of one. As it is quite heavy it tends to displace the air when a stream of the gas is directed a t the base of a flame. Thus the carbon dioxide gas produces a blanketing effect about the fire, shutting out or diluting the oxygen supply necessary for the combustion. The gas has the advantage over water of being non-corrosive and of leaving no liquid or solid residue, as will water or water solutions. Naturally, it can cause no water damage. It is a well-known fact which is painfully realized by fire insurance companies that the damage caused by water in extinguishing- a

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fire is often far greater than the actual fire damage. On the other hand, the b l a n k e t i n g e f f e c t which carbon dioxide produces is not permanent but is quickly dissipated. Therefore, carbon dioxide is not efficient in extinguishing fires of ordinary combustible materials, like wood, paper, etc., and is not recommended for this purpose. In low concentrations this gas is not injurious. For this reason it is not generally classed as a poisonous gas. However, a number of people have died in the p a s t b y breathing air rich in carbon dioxide in industrial work (2). A? atmosphere containing a large enough quantity of this gas to extinguish fire cannot sustain human life. Consequently, death might result from toxic action. Carbon dioxide has the disadvantage of being odorless and consequently gives no warning of its presence even when in fatal concentrations. Carbon dioxide will cause death in a concentration of about 10 per cent. when breathed for a comparatively short period of time ( 3 ) . The employment of first-aid portable carbon dioxide extinguishers is thus limited to a few specific fires. Its use is recommended for two types of Class B and C fires only, namely: fires in open tanks of flammable liquids such as gasoline, and fires in electrical switchboard rooms of telephone exchanges and other places of a similar type. The use of these extinguishers is further limited to relatively small fires of the types indicated, because the operator of the extinguisher must stand very close t o the fire in order to be able to extinguish it effectively. Wind conditions seriously affect the efficiency of this type of extinguisher. In these extinguishers the carbon dioxide is compressed to the liquid state under a pressure of 850 lb. per sq. in. at 70°F. (21.11°C.). The pressure, of course, varies with the temperature, this being a two-phase, ~ne-componentsystem. The pressure is lowered at -40°F. (-40°C.) to

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135 lb. per sq. in. and increases to 1400 lb. per sq. in. at a temperature of 140°F. (C,O°C.). Every approved, portable, first-aid carbon dioxide extinguisher is equipped with a safety disk which opens when the temperature becomes so high that the pressure is increased to 2400 lb. per sq. in. These carbon-dioxide extinguishers are equipped with either a quickrelease seated valve or else a s~ecialvalve that oierces a safetv seal. In the first case, the gas will be expelled from the extinguisher as soon as the quick-release seated valve is opened; in the other case, the passage of the carbon dioxide through the hand hose an'd the cone nozzle is not possible until the safety seal has been punctured by the special valve used. The portable extinguishers are made in sizes varying from 7'/2 to 100 lb. of carbon dioxide. Besides these portable extinguishers, there are in use permanently piped systems of carbon-dioxide cylinders (Figure 4), either single or in batteries. Permanently installed pipes lead from these systems to specific fire hazards such as fur storage vaults, special electrical equipment, and places where flammable liquids are stored and handled. These piped systems may be manually or automatically operate5 and mechanically or electrically controlled. Some of these systems are particularly adapted to marine use and are built for boats, yachts, sea sleds, cruisers, and the like. The capacities of the cylinders in these units vary from 71/2 to 50 lb. of carbon dioxide. According to the specificationsof the U. S. Steamboat Inspection Service, the extinguishers must be supplied in duplicate in order that protection may be maintained after using one set. I t is also required that in the holds of vessels, sufficient carbon dioxide must be a t hand (in duplicate) to fill the hold with a 30% mixture of this gas, the boiler room requiring only a 25y0mixture of carbon dioxide. Naturally, the steel cylinders must be stoutly built to hold this gas, and they are consequently very heavy. The relatively great weight of the steel cylinders, as well as the size of the apparatus compared to the amount of the extinguishing gas contained, offers a drawback to the use of this type of extinguisher where space and weight are at a premium.

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Carbon Dioxide Plus Water Water expelled by carbon dioxide under pressure is used to extinguish fires. The most common of this type of extinguisher is the so-called soda-acid fire extinguisher. The chemicals used are a saturated aqueous solution of sodium bicarbonate and commercial sulfuric (66' Banme) or hvdrochloric acid. The two reagents, . which are k e ~ tin seDarate containers within the extinguisher, are brought together whenever the extinguisher is to be used. These soda-acid extinguishers are particularly effective on all types of. incipient Class A fires in free-burning materials-such as wood, rubbish, paper, highly flammable surface coatings, etc., where the quenching and cooling effect of the fire-extinguishing agent is of the utmost importance. They should never be used for electrical fires, as the electric current will follow the stream of the solution which is a conductor and, in cases of high voltage, may seriously injure the operator, as has happened in the past. Neither should they be used for flammable liquids as they would merely duplicate the before-mentioned effect of water on such fires. There are mainly two types of soda-acid -extinguishers; the loose-stopple type and the break-bottle type. Every student taking freshman chemistry is probably acquainted with the appearance and mechanism of a soda-acid extinguisher of the loose-stopple type. Figure 5 shows a small extinguisher (ll/z to 2l/2 gallons). The larger sizes (17 t o 80 zallons) are mounted on wheels 1 and are either hand-drawn or else motorFmURE -SMALL SODAdriven. Some of these larger extinguishers are ACID EXTINGUISHER OR THE used in factory and warehouse buildings, LOOSE.STOPPLE TYPE others in mill yards and similar places, or in village and town fire department service. There are also stationary systems in sizes of 100 to 200 gallons. The soda-acid extinguishers of the loose-stopple type consist of two compartments, a small one and a large one (Figure 6). I n the small compartment or bottle cage is an eight-ounce glass bottle fitted with a loose stopple and filled up to a mark designated as the acid line with four ounces of sulfuric acid. This bottle is suspended in the upper part of the large con-

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L.

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tainer which is filled with a concentrated solution of sodium bicarbonate up to the water mark. Upon inversion of the extinguisher, the stopple drops down, the acid flows out and reacts with the bicarbonate of soda solution, generating carbon dioxide. The large amount of gas thus suddenly formed exerts a pressure upon the water and expels i t with considerable force. An efficientextinguisher should eject a stream about 40 feet in any one direction. The duration of the stream is one minute at 6YF. (18.33'C.), and,the stream should be neutral to litmus paper. These extinguishers should be protected against frost as they are not efficient a t low temperatures. Furthermore, they should be emptied, cleaned, and charged every year to guard against deterioration of the solution. Figure 7 shows a European-made soda-acid extinguisher of the break-bottle type. This type of extinguisher differs from the one shown in Figure 5. A sealed glass tube containing hydrochloric acid takes the place of theloosely stoppled bottle. This glass tube is broken by the insertion of a knob (Figure 8) located on the outside of the extinguisher. Thus the acid is brought into contact with the solution of sodium bicarbonate, liberating carbon dioxide., The functioning of the extinguisher is similar to the local product from this point. Ordinary water, as well as the solution of calcium chloride or the solution ejected from a soda-acid extinguisher, is useful in extinguishing most ordinaryfires, but it is an aid of rather questionable value in some instances. The damage done by the water in extinguishing a fire is often two or three times as great as the damage done by the fire. The stream ejected from a soda-acid extinguisher will be acid in character if the solution is not properly prepared, the acid bottle improperly designed or improperly filled or the mixing of acid with soda solution not properly proportioned, and this free acid adds its destructive Dower to that of the water. If the extinguisher bears the inspection label of the Underwriters' Laboratories or that of the Associated Factory Mutual Laboratories, it is evidence that the extinguisher and charge sold for it have been tested and found to be

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safe and satisfactory for use, in which event the stream will be neutral and the pressure generated not excessive, provided that the extinguisher has been charged according to instructions.

Foam as a Fire-Extinguishing Agent Foam is formed when the carbon dioxide, produced by the chemical reaction which takes place upon the mixing of the two solutions contained in the foam-type extinguisher, is trapped in the form of minute bubbles due to the introduction, generally in the alkaline solution, of a substance designed to change the surface tension conditions of the solutions. The two solutions are made up in equivalent amounts and containedin separate compartments within the extinguisher (Figures 9 and lo), which in outward appearance resembles the construction of the loose-stopple type soda-acid extinguisher. The

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SHOWN IN FIGURE 7 EXTINGUISHER times called, which is the ina. Cone-shaped, lead-coated sheet-iron shell gredient employed to change the containing the aqueous solution of sbdiurn bicarbonate surface tension of the solutions, b. Cap of nickeled brass, air- and water-tight is usually dissolved in the alka- c. Lead-coated handle, riveted to shell line or carbonate solution con- d. Lead coated, perforated metal basket with ring a t bottom tained in the Outer Or larger e. spiral Acid glass tube resting on spiral ring within compartment of the extinthe basket ( d ) ejection tube, attached to inside guisher, while the aqueous acid- f. Lead-coated of tank, opposite t o handle, and leading to reacting solution, which is gennozzle (i) Screened inlet to ejection tube (f) erally much smaller in bulk g. h. Nickeled piston, with plate on each end, than the alkaline solution, is which breaks acid glass tube (e) when struck contained in the in- c. Nickeled brass nozzle with diagonal bore, screwed to pointed end of shell (a) serted compartment. On inversion of the extinguisher, the solutions react, producing carbon dioxide


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which results, first, in the development of pressure and, second, in the production of foam upon the automatic release of this pressure. In this foam the solution forms a very thin film which is extended by the bubbles of carbon dioxide, and is maintained for several hours in spite of the fluidity and high density of the water. Thus the foam cannot flow off the burning surface but remains as a blanket on top of the material. Ordinary water drops off an object, particularly a burning object, in a very short period of time; foam, which has a low specific gravity-0.12-0.15-and hence is lighter than the lightest oils, will stay there much longer. Due to its low su~facetension, the foam forms a light and solid fireproof cover over the burning object and excludes fhe oxygen from i t for a much longer time than water could possibly Furthermore, the volume of foam formed is much larger than the volume of water used in producing this foam. To illustrate, the volume of water in a 21/1-gallon soda-acid extinguisher is about the same as the volume of water in a 21/2-gallon foam-type extinguisher. The quantity of the product formed by the two extinguishers is quite different, however. The soda-acid extinguisher ejects only 21/2 gallons of solution, while the foam-type extinguisher produces about 25 gallons of foam. In other words, one gallon of water present in the two solutions will release, on mixing, approximately ten times its volume or ten gallons of practically air-tight foam. Foam is effectivefor all types of Class A and Class B fires. It is particularly efficient in extinguishing burning liquids, such as petroFIGURE O - 4 FOAMTVPC FIRE leum, gasoline, benzine, oil, tar, lacquers, carExnwcrrnwm bon &sulfide, benzene, turpentine, toluene, naphtha, enamel, wax, grease, shellac, etc. It should be on hand at all plants in which volatile, combustible liquids are produced or used, such as coal distillates, by-products of gas manufacture, benzine used for dry cleaning, tar distillates, lubricants, combustible liquids employed for vulcanization, and soap and candle manufacture, etc. Batteries of foam extinguishers which need not be operated manually are sometimes installed for specific fire hazards. At the top there is a ~~~

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~

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release which automaticallv inverts the extinruishers a t the outbreak of a fire in the place protected. Some of the larger types of foam extinguishers (Figure 11) do not contain solutions of the two ingredients a t all; the chemicals, together with the stabilizing agent, are kept in the dry state. When such an extinguisher or foam generator or accumulator, as i t is called, is to be used to extinguish a fire i t is attached t o a constant water supply through a hydrant or a pipe system. The water dissolves the chemicals and foam production takes place subsequently, as described before. Foam extinguishers, containing the two solutions, must be protected against freezing. This is not necessary in the case of these accumulators which utilize the dry powder.

Figure 12 shows a tank filled with gasoline and oil which has caught fire. Figure 13 shows the white foam flowing over the surface of the oil, excluding the air, and pushing the flame toward the edge of the tank. Figure 14 demonstrates how the remainder of the flames are suppressed completely by the creation of a uniform, compact foam blanket. An added advantage of the

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foam extinguisher is the fact that the fire cannot re-ignite once it has been extinguished. This is due to the fact that the foam remains there, which is not true in the case of water or carbon dioxide which remain for only a short period of time. The principle of the 21/2-gallonunit is made use of in the extinguisher of larger volume through the portable extinguishers of 10 and 40 gallons to the large stationary systems used by the 08refineries. The writer has consistently refrained, in the description of the foam-type extinguishers, from mentioning the specific names of the chemicals employed or the concentrations of the solutions used because this always presents a temptation to those who possess such extinguishers to endeavor to make up their own charges-a practice which is not advised and which has caused loss and trouble to both the user and the manufacturer of the extinguisher after an attempt to use the extinguisher in an emergency. Simple as the chemistry involved may seem, the combination of the chemistry and the mechanics of the extinguisher presents difficulties which have required extended experimenting and ingenuity to produce a satisfactory and efficient extinguisher. It is also advised that the charge designed to accompany the extinguisher of a certain make be used exclusively in that extinguisher if the highest efficiencyis to be attained in its use. Carbon Tetrachloride as a Fire-Extinguishing Liquid Carbon tetrachloride belongs to the class of those rather few organic compounds that neither explode nor burn. It is a heavy, colorless liquid,

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has a specific gravity of 1.584, boils at 76'C. (168.S°F.), and freezes at - 19.5'C. (-3'F.). Carbon tetrachloride is the main constituent of firefighting liquids such as Pyrene, Fire Gun, Fyr-Fyter, and others. These liquids are carefully treated and tested for purity and dryness, and contain, in addition, various chemicals which reduce the freezing point to about -45'C. (-4g°F.). A fire-fighting liquid having a carbon tetrachloride base has many of the good points of the exting~ishingchemicals already

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mentioned, with other advantages. It is a dry chemical and therefore causes no water damage. It extinguishes fires partly by its cooling action due to its volatility, whereby the temperature of the burning object is lowered (although not as efficientlv as when usine" water) below its ienition " or kindling point; in this respect its action is similar to that of water. Furthermore, both carbon tetrachloride and dry carhon dioxide extinguish fire by virtue of the heavy non-combustible gas produced, which excludes the air and thus extinguishes the flame; carbon tetrachloride gas, however, is 31/2 times as heavy as carbon dioxide and therefore much more efficient. Tests carried out by the U. S. Bureau of Mines have shown that carbon tetrachloride vapor has 2.43 times the fire-extinguishing power of carbon dioxide gas (1). Another advantage over carbon dioxide is its characteristic odor. When dry carbon dioxide is used, the toxic concentration of this gas may be reached quickly without any warning to the operator of the extinguisher. This is not possible in the case of carbon tetrachloride which would drive the operator away-due to the odor of the vaporslong before the toxic concentration is reached. It should be noted that whiie small quantities of gases deleterious to health may be produced from chemicals used for extinguishing fires, there is no danger in the application of these mediums t o iires under ordinary conditions, since there is usually sufficient ventilation to dissipate any gases that may be formed. No toxic substance is known which is poisonous in all concentrations. Fumes are not dangerous to health unless present in amounts of well-defined limits and breathed for a sufficiently long time. The fact that small amounts of these "toxic" gases may he I ~ I G U K1 3E. - c ~ n B O N TETRACHLUR~E TYPEEX- produced from fire-extinguishing agents under TINGUISHER carefully controlled laboratory conditions has given rise to many misleading and erroneous statements in the literature. Fire itself in certain combustibles will produce such poisonous gases as carbon monoxide, hydrogen sulfide, hydrogen cyanide, nitric oxide, and

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others. These gases may be produced in large quantities and the danger to health becomes serious if the fires are not extinguished immediately by the use of properly selected fire-extinguishing chemicals. In confined, unventilated spaces, the atmosphere may become toxic from the products of combustion. Fatalities are not uncommon from carbon monoxide produced from burning material that has not been extinguished quickly. One of the most important advantages of carbon tetrachloride is the fact that it is a non-conductor of the electric current and hence can be used for electrical fires. I t is an insulator having a dielectric constant of about 10,000 volts per '/lol.

To demonstrate the fire-extinguishing property of carbon tetrachloride support a burning candle or porcelain dish containing burning gasoline in a tall cylinder. Burn a piece of paper over another cylinder and pour some carbon tetrachloride over the burning paper. The transparent and colorless vapors from the carbon tetrachloride will become visible due to the solid smoke particles. Now pour the visible cloud into the first cylinder and note the extinction of the flame as soon & the .Icloud comes in contact with it. The carbon tetrachloride-type fire extinguishers vary in size from one pint to two gallons. Figures I5 and 16showsmallAmerican-made extinguishers. Figure 16 shows a fire extinguisher operated by a double-acting, centrally located rotating liquid pump. Some extinguishers are operated by air pressure built up by several strokes of the pump and maintained by pumping. Both types of extinguishers have been approved by the Underwriters' Laboratories and bear their label. The larger carbon tetrachloride extinguishers operate under gas pressure of either air (Figure 17) or Co,,,c,,os CARBON carbon dioxide. TETKACHLOR~DE-TYPE ExCENTRAL There are two one-quart extinguishers es- T I N C U I ~ H BPRWITH ,,~P pecially built for airplane protection. The first one is known as an air-pressure type extinguisher. It is charged with air under a pressure of 100 lb.; this pressure can be read on the pressure gage located on the top of the extinguisher. The extinguisher

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consists of two containers. The outer container holds the fire-extinguishing liquid, while the inner container holds the air under pressure. By turning a control valve lever outside of the extinguisher, a dual control valve inside of the extinguisher is also turned. When this dual control valve, which connects the two containers, is thus opened the air enters the liquid container, opens the discharge valve and thus forces the extinguishing liquid out onto the fire under the pressure of 100 lb. The second airplane fire extinguisher is of the gas cartridge type; it is smaller, lighter, and much simpler in construction. A small steel cartridge containing liquid carbon dioxide under pressure is located within the extinguisher in a cradle at the mouth of the shell a., Turning the operating lever of the extinguisher I.. punctures this cartridge and opens a discharge orifice. The carbon dioxide thus suddenly released from the cartridge exerts a pressure upon the fire-extinguishing liquid and expels it under pressure. I t is interesting to note in this connection that airplane fire extinguishers of the type shown were used by Commander Byrd on his trip to the South Pole. . Figure 18 shows two gas-cartridge extinguishersinstalled in the "Stars and Stripes,'' a Fairchild Cabin Monoplane of the expedition. Many fires occur with motion-picture projection machines. The most satisfactory chemical that can be used safely to extinguish such fires is carbon tetrachloride. An interesting adaptation of this chemical t o the particular conditions accompanying fires in motion-picture projection machines has been made. The extinguisher devised, which is of the gas cartridge type, is mounted directly on the motionpicture projection machine. At the first flash of flame within the projector, a fuse melts due t o the action of a special heat primer or flame attractor attached to the fuse opening the cartridge. The carbon dioxide expels the liquid under pressure through spray nozzles into no less than five different parts of the machine. At the same time, the mechanism of the extinguisher shuts off the electric current both on the light and on the cut-off switch automatically, thus stopping the motor.

VOL.9, NO.9


I t is highly advisable that all fire extinguishers be charged only with the specific chemicals supplied by the maker of t t e extinguisher. This is necessaty since impure chemicals often cause corrosion in the interior mechanism, or reduce the extinguishing qualities of the apparatus. The Underwriters' Laboratories have made a specific recommendation to this effect. Other Chemicals and Extinguishers I t is impossible to discuss in a brief paper all kinds of chemicals and extinguishers that are being used a t the present time. Most of the important ones, however, have been mentioned. When in doubt as to whether a particular fire-protection appliance has been accepted by the authorities it is only necessary to find out whether i t has been approved by the organizations already mentioned. There are several types of chemicals and extinguishers which have not been approved a t all, namely: dry-powder extinguishers and extinguishers in glass tubes and glass bottles, which commonly come under the nomenclature of hand grenades. The Inspection Department of the Associated Factory Mutual F i e Insurance Companies makes the following statement with regard to the dry-powder type extinguishers: "In view of the fact that several so-called fire ex-

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SEPTEMBER, 1932

tinguishers, consisting generally of sheet-metal tubes filled with mixtures of bicarbonate of soda and other materials in powder form, have been widely advertised, the Inspection Department has t o report that, in its opinion, all fonns of dry-powder fire extinguishers are inferior for general use, that attempts to extinguish fires with them may cause delay in the use of water and other approved extinguishing agents, and therefore their introduction is discouraged." Literature Cited ( )

JONESAND PERROTT,"Extinction of Methane Flames by Dichloro-Difluoro Methane," U. S. Bureau of Mines, R. I. 3042. "Effect on Workers of Air Conditions," U. S. Bureau of Mines. I. C. 6439. (1') SAVERS, "Industrial Poisoning from Fumes, Gases, and Poisons of Manu(:i) RAMBONSEK, M . L R G G ~Edward . Arnold,London, facturing Professes." Translated by THOMAS 1913, p. 200.

SOME ELEMENTARY LABORATORY PRECAUTIONS AGAINST FIRE Prevention is better than cure. Preventive measures fall into two chief classes: (1) those designed to avoid the outbreak bf fires, and (2) those designed to minimize the effects of fires which may break out. .E In the former class obvious details of laboratory technic rank high. Avoid handling volatile or combustible chemicals near open flames. Heat volatile or combustible liquids only in a bath or on a hot p l a t e n e v e r aver a direct flame. I n distilling such liquids, collect in a stoppered filter flask with a tube leading from the side-arm t o hood, running drain, or outside air. Inspect all student set-ups before they are placed in operation. Insist that all active chemicals be disposed of in suitable ways. The waste jar is no place for them. I n the second class. storaae important. Volatile, combustible, -~ - of chemicals is highly and explosive chemicals should he as remote as possible from working spaces or electrical eouioment where fire might conceivably break out. (Incidentally good light should be available so that there is no temptation to strike a match t o read labels.) Juxtaposition of individually harmless chemicals dangerous in combination should be avoided. Fire-fighting apparatus should be conspicuously available and should include foamtype equipment. Prominent placards should designate the class of fire for which each particular type of apparatus is suitable. I n the excitement attending a fire these would probably not be read but students will already know their general content and may retain sufficient presence of mind to seize the proper one in an emergency. Do not use carbon tetrachloride on alkali-metal fires. A few sand-buck& constitute an admirable supplement t o conventional fire-fighting equipment. Keep moll

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Extinguishing fires with chemicals - ACS Publications - American

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