Extinguishing of Fires in Oils and Volatile Liquids
GENERAL NEWS ARTICLES
The extinguishing of fires in oils 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 _____nsatisfactorlly 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 purpose of this paper to discuss these materials and the conditions under which they prove the most efficient.
Not all fires in volatile liquids arc difficult to handle with water When 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 bf 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 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 he made use of in extinguishing fires in volatile oils are (a) to form a blanket either of gas or of sotid 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 longhandled, 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 on thin liquids, since it floats more readily mi the former than on the latter. The sawdust itself is not easily ignited, and wthen 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 he of little ot 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 effect 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 decreases 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 ready source of ignition.
Although the efficiency of sawdust is greatest on-vicous liquids such as lacquers, heavy oils, Japan, waxes, etc., in the tests 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 hicarbonate mixture does not work so well since the saw-dust s-inks before the whole surface can be covered, whereupon the exposed liquid reignites.
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 1,682 at 32 degrees Fahr. It is non-inflammable; non-explosive and is readily miscible with oils, waxes, japan, etc. When mixed with inflammable liquids it renders them non-inflammable 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 in paragraph three, namely, it dilutes the inflammable liquid, rendering it non-inflammable, 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 paper 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 nature of the fire. In tank fires 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 if upon the floor is. as would he expected, of considerable importance. In tanks larger than about 28×12 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 60×30 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 carbon 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 extiguisher 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 hand-pumping arrangement would probably be unsatisfactory, and it would therefore he necessary to force it out in some other way.
A few systems have recently been installed in which an elevated tank containing carbon tetrachloride was connected with automatic sprinklers or perforated pipes located in hazardous rooms where volatile and inflammable liquids are in use. So far as is known none of these systems have as yet been called upon to extinguish a fire, but there appears to be no reason why such a system should not provide excellent protection in special cases. In such systems it would be necessary to consider the safety of the workmen and furnish ready means of escape, since carbon tetrachloride is an anesthetic and where thoroughly sprayed through the air as from an automatic sprinkler it would probably produce rapid results.
The nature and effect of the fumes given off When carbon tetrachloride is thrown upon a fire is a subject which has received a great deal of discussion. When the liquid comes in contact with a fire the vapor is partly decomposed, resulting in the evolution of a considerable quantity ot black smoke, which is undoubtedly finely divided carlton. Pungent gases are also produced which appear to be mostly hydrochloric acid with possibly a small amount of chlorine. Since carbon tetrachloride contains no hydrogen from Which hydrochloric acid could be formed, this substance must be produced by the action of chlorine on the gases arising from the burning material or upon the moisture of the air.
The fumes of carbon tetrachloride, although of a very pungent nature, do not produce any permanent injury under ordinary conditions where the operator can make his escape after he has inhaled all that he can stand, but they are a distinct handicap in fighting a fire, and are one of the objectionable features to carbon tetrachloride as a general fire extinguishing agent. In large rooms or where a small quantity of carbon tetrachloride is sufficient to extinguish a fire the gases are of course less objectionable.
Another method of extinguishing fires in oils and volatile liquids, which, has recently been proposed and experimented with is that of using frothy mixtures. The idea seems like a very promising one and the tests which have been thus far reported indicate very satisfactory results. The idea was originated and has been developed in Germany. So far as is known, no experiments have been conducted in this country.
The process consists essentially in causing two liquids to mix in a tank where foam is produced. The tank is made air-tight and sufficiently strong to permit of the foam being forced out by carbon dioxide under pressure, and the foam is conveyed to the fire by means of a line of hose. The exact nature of the liquids has not been disclosed. but one of them probably consists of a sodium carbonate solution containing froth-forming ingredients, such as glue or casein, and the other an alum solution The two on coming together generate carbon dioxide which produces ftoth. This froth is reported to be quite stiff and to shrink in volume but a comparatively small amount even after a period of half an hour.
A number of tests were conducted in the winter of 1912 in Germany; some of them on a considerable scale. In one case as much as five tons of crude naphtha in a tank was involved, and in another an area of 1,300 square feet of burning tar was used. In all cases the results were reported satisfactory, the fires being extinguished in a Short time.
The frothy mixture undoubtedly owes its efficiency to its blanketing action in settling upon the surface of the burning liquid, thus excluding the oxygen of the air, and to the fact that the bubbles of liquid contain carbon dioxide, which, upon bursting, produce an atmosphere in which combustion cannot take place.
According to the latest reports the matter is still in an experimental stage, various details regarding the form of apparatus, most efficient pressure, and design of nozzles being under consideration; but from what has already been done, it would appear that the idea is a very promising one. and that this method of extinguishing fires in oils and volatile liquids will prove to be by far the most efficient of any that has as yet been suggested.