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WATER AND ALCOHOL SOLUTIONS
Water 95%, Alcohol 5%.
Freezing point, 25° F.
WATER, ALCOHOL AND GLYCERINE SOLUTIONS
Water 85%, Alcohol-Glycerine 15%....Freezing point, 20° F.
EXTRACTS FROM A PAPER READ BY EDW. H. BARRIER BEFORE THE AMERICAN SOCIETY OF MECHANICAL
Extinguishing Fires in Volatile Liquids. The extinguishing of fires in oils, gasoline and in most of the volatile liquids has always been a difficult problem and where fires of this kind occur the results are frequently very disastrous. Our most common extinguishing agent, water, works rather unsatisfactorily upon the majority of such fires, but it is still the only one available where heroic measures are required. Comparatively recently, however, there have been two or three other materials introduced for use as extinguishers which have shown some promise for dealing with these fires, and it is the writer's purpose to discuss these materials and the conditions under which they prove the most efficient. Not all fires in volatile liquids are difficult to handle with water. When the liquid is miscible with water this extinguishing agent can be successfully used. Examples of this kind are denatured alcohol, wood alcohol, grain alcohol, acetone, etc. Where the liquid is not miscible with water little or no effect is produced except to wash the burning liquid out of the building where it may be completely consumed, or, if the quantity of oil is small, possibly to extinguish the fire by the brute cooling effect of a large quantity of water sprayed upon the fire. Soda and acid extinguishers are somewhat
PER CENT ADDED TO WATER
10 DEGREES BELOW ZERO
10 15 20 25 30 DEGREES ABOVE ZERO
Fig. 466.—Charts Showing Freezing Points of Various Mixtures of
Calcium Chloride, Alcohol, etc., and Water.
more effective than pure water, but even they fail under most conditions. The various grenades containing salt solutions which were formerly extensively exploited are of course practically worthless. The only principles that can be made use of in extinguishing fires in volatile oils are (a) to form a blanket either of gas or of solid material over the burning liquid which will exclude the oxygen of the air or (b) to dilute the burning liquid with a non-inflammable extinguishing agent which is miscible with it.
Sawdust and Bicarbonate of Soda.—To the blanketing type of extinguishers belongs sawdust. Paradoxical as it may seem, ordinary sawdust is an excellent extinguishing agent for certain volatile liquids, especially those of a viscous nature. A considerable number of experiments were conducted in the fall of 1912 by the inspection department of the Associated Factory Mutual Fire Insurance Companies, in the extinguishing of fires in lacquer and gasoline in tanks with sawdust, and the results were surprisingly satisfactory. The liquids were placed in three tanks 30 inches long, 12 inches wide and 16 inches deep; 48 inches long, 14 inches wide and 16 inches deep; and 60 inches long, 30 inches wide and 16 inches deep. The sawdust was applied with a long-handled, light but substantially built snow shovel having a blade of considerable area. In every case the fires were extinguished readily, especially in the two smaller tanks which were about as large as any ordinarily employed for lacquer in manufacturing establishments. The efficiency of the sawdust is undoubtedly due to its blanketing action in floating for a time upon the surface of the liquid and excluding the oxygen of the air. Its efficiency is greater on viscous liquids than thin liquids, since it floats more readily on the former than on the latter. The sawdust itself is not easily ignited, and when it does become ignited it burns without flame. The burning embers have not a sufficiently high temperature to reignite the liquid. The character of the sawdust, whether from soft wood or hard wood, appears to be of little or no importance, and the amount of moisture contained in it is apparently not a factor, so that the drying out of sawdust when kept in manufacturing establishments for a time would not affect the efficiency. It was found that the admixture of sodium bicarbonate greatly increased the efficiency of the sawdust as shown both by the shortened time and the decreased amount of material necessary to extinguish the fires. A further advantage of the addition of bicarbonate of soda is that it decreased the possible danger resulting from the presence of sawdust in manufacturing plants since it would be difficult if not impossible to ignite the mixture by a carelessly thrown match or any other source of ignition. Although the efficiency of the sawdust is greatest on viscous liquids such as lacquers, heavy oils, japan, waxes, etc., in the test referred to, fires were extinguished in gasoline contained in the smallest tank and also when spread upon the ground. In larger tanks the sawdust or bicarbonate mixture does not work so well since the sawdust sinks before the whole surface can be covered, whereupon the exposed liquid reignites.
Carbon Tetrachloride.-In recent years carbon tetrachloride has received considerable attention as a fire extinguishing agent. This is due largely to the activity of certain manufacturers of fire extinguishers which use liquids, the basis of which is carbon tetrachloride. This substance is a water white liquid and possesses when pure a rather agreeable odor somewhat similar to chloroform. A considerable proportion of the commercial article upon the market, however, contains sulphur impurities which impart a disagreeable odor to the liquid. The substance is quite heavy, its specific gravity being 1.632 at 32 degrees Fahr. It is non-infiammable, non-explosive, and is readily miscible with oils, waxes, japan etc. When mixed with inflammable liquids it renders them noninflammable provided a sufficient quantity is added. Its vapor is heavy, the specific gravity being about five and one-half times that of air, consequently it settles very rapidly. As an extinguishing agent it operates by both the principles mentioned, namely, it dilutes the inflammable liquid rendering it non-flammable, or at least less inflammable, and it forms a blanket of gas or vapor over the burning liquid which excludes the oxygen of the air.
Although this exposition is confined to a discussion of extinguishing fires in oils and volatile liquids, it may not be out of place to mention that the claims made by certain manufacturers producing extinguishers which use liquids, the basis of which is carbon tetrachloride, are grossly exaggerated. These preparations, none of which is more efficient than carbon tetrachloride, are not the equivalent of the ordinary water extinguishers for general use on such materials as cotton, wood, paper, oily waste, etc. On volatile liquids, oils, etc., carbon tetrachloride has, however, shown very satisfactory results under some conditions, but the readiness with which a fire can be extinguished with it depends to a considerable extent upon the skill of the operator and the length of time that the liquid has been burning is an important factor, and in such cases where the sides of the tank become heated the only way in which the fire can be extinguished is to squirt the liquid forcibly at the sides. If the carbon tetrachloride is squirted directly into the liquid it is much more difficult, if not impossible to extinguish the fire. The height of the liquid in the tank is also a very important factor. Where the liquid is low the sides form a pocket which retains the vapor and aids considerably in smothering the blaze. When the tank is nearly full, however, this condition does not exist, and it is then very difficult, if not impossible, to extinguish a fire in a highly volatile liquid such as gasoline; only the most skilled operators are successful in these cases.
The size of the tank or the extent of the fire upon the floor is, as would be expected, of considerable importance. In tanks larger than about 28 inches by 12 inches more than one extinguisher and operator working at a time are necessary to extinguish a fire in such materials as gasoline. In one test where a tank 60 inches by 30 inches was used no less than seven operators were necessary, and even then it was only with the greatest difficulty that the fire was put out. All of the above remarks apply to tetrachloride in the ordinary one quart extinguisher as generally sold. It is probable that a large extinguisher which could throw a large stream would prove more efficient, but on account of the great weight of carbon tetrachloride such an extinguisher would have to be specially designed to make it readily portable by mounting on a truck or some similar means. Expelling the liquid by means of a handpumping arrangement would probably be unsatisfactory, and it would therefore be necessary to force it out in some other way.
A few systems have recently been installed in which an elevated tank containing tetrachloride was connected with automatic sprink