Methods of Extinguishing Incendiary Bombs' MAJOR EARL A. SHRADER Chemical Wa.rfare Service, United States Army
itself as by the fire started as a result of incendiary action. The problem of control of incendiaries, therefore, is to interrupt the cycle of incendiary action and prevent the enemy from accomplishing his incendiary mission-the start of a conflagration. In the incendiary cycle, based on the principles of combustion, there must be a balance established between the intensity of heat attained and the time during which that intensity is applied. Any incendiary munition can be judged by the relationship established between these two factors. The design and composition of a particular incendiary munition will depend upon the specific mission to be accomplished. Thus a number of kinds of incendiaries have been developed. The idea that explosive bombs per se would start enough fires to cause widespread destruction from this source led to the belief that there was no necessity for a special "incendiary" munition. This reasoning was based on the fact that the detonation of an explosive bomb liberates an enormous amount of kinetic energy in the form of heat. Theoretically this would account for the intensity factor, but the heat thus generated is dissipated in the fraction of a second. Thus, the time factor being insignificant, there is not a proper balance established between the factors. Analysis of records from a great many aerial attacks reveals that not more than one per cent of the fires started were traceable to the explosive bomb. Therefore, in order to accomplish the purpose of incendiaries, we need another kind of munition with a better relationship between these factors. The one incendiary we have been able to get that gives the best balance between the necessary factors is the magnesium incendiary bomb. The burning temperature of the magnesium bomb is 3630°F. and the time of burning about 10 minutes. It is evident from these figures that such an intensity of heat applied over Paper presented at the "Symposium on Civilian Preparedness such a period of time would ignite any material that is for Chemical Warfare" conducted by the Division of Chemical Education at the Detroit Meeting of the American Chemical combustible and near enough to be subjected to the application of heat from the burning bomb. Society. April 13, 1943.
HE SUBJECT "Extinguishing Incendiary Bombs" to my mind includes more than the mere consideration of those materials which may be applied to the burning chemical substances composing the bomb. There should he included in an academic discussion such as this (and I use the term academic advisedly because we will not be able during this short period to carry out any practical application of the subject) some consideration of the factors influencing the use of incendiaries. Let us develop the theme around the following: 1. Technique, or the technical characteristics of incendiary munitions. 2. Tactics, or themilitary employment of incendiaries. 3. Controls, or the measures employed to avert the spread of fires from incendiaries. If we keep in mind that modem aerial warfare employs both high explosive bomhs and incendiary bombs either alone or in combination, and understand the potentialities of such employment, then the efficiency and limitations of control measures may be more fully appreciated. An indication of the increasing importance of the incendiarv bomb as a militam weauon is evident from the fact that in recent attacks, the weight of incendiary bombs carried has equaled and sometimes exceeded the weight of'explosive bombs. The objective of civilian protection is to minimize the damage caused by aerial bombs, and as a general proposition i t is possible to do more to limit the damage from incendiary bombs than to limit or reduce the damage from explosive bombs. The reason for this is that damage caused by high explosive bombs follows immediately and directly as a result of the impact and explosion of the bombs. But the damage from an incendiary bomb is not caused so much in every instance by the direct action of the bomb
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As you probably know, the thermit bomb produces the exceedingly high temperature of 4330°F.during the course of the chemical reaction which takes place in burning of this bomb. But keep in mind that the actual burning is completed within one minute and the residue of hot molten iron commences to cool off rather than continue to disseminate heat. Here we have plenty of heat, but the weakness of this bomb lies in the short application factor. On the other hand white phosphorus may burn for ten minutes or longer but the heat evolved will do no more than char the most superficial layers of any wooden surface with which it comes in contact. The relationship of the factors is off balance in the other way in the case of this munition. I n the technique of incendiaries it seems that nothing can be more important than these two factors. A realization of this important balance and its application will enable us to gage the efficiency and need for control of any incendiary munition with which we come in contact. Let us now turn our attention to the tactical use of incendiaries, which means the attempt of the military to apply the appropriate incendiary to the target. Essentially this involves the two problems of selecting an incendiary munition which is appropriate to the mission and the placing of the selected munition a t and not merely near the target it is supposed to ignite. Fundamentally, we think of the explosive bomb being used against noncombustible targets only and the incendiary bomb being used against combustible targets. But we must also consider those situations in which the explosive bomb produces debris which is combustible and exposes structural elements which are combustible to subsequent action of incendiaries. Let us consider for a moment an industrial plant surrounded, as many are, by the homes of the workmen. The plant may be of such construction that incendiaries would have little or no effect, but high explosive would put the plant out of operation. On the other hand, the homes of the workmen would be proper targets,for the incendiaries. An attack using a combination of the two munitions would in such a situation drive the workmen from their homes, shut down the plant, and result in a prolonged delay in production while rehabilitation and reconstruction took place. There are some plants, however, against which an incendiary bomb would prove particularly effective, due to presence of highly combustible materials used in the processes of manufacture. You as chemists need not be told of these industrial hazards, which exist under normal conditions. How much more hazardous, then, they would become under an aerial attack must be apparent to you. The proper tactics involve the selection of the proper bomb to accomplish the purpose of the mission. The proper size bomb to cause physical destruction and the proper type of incendiary to fire the buildings or materials will be governed by the particular target attacked. There is another point in regard to explosive muni-
tions which probably has not received as much consideration as it merits, and which has a decided effect on the handling of incendiaries. It must be kept in mind that high explosives are definitely antipersonnel in effect in addition to the effects on mat6riel. The use of high explosives in conjunction with incendiaries would definitely tend to discourage the activities of personnel in an attempt to attack and contrpl the incendiaries. If individuals who are capably trained in the methods of handling incendiaries or the resu!tant fires can be forced to delay their control measures, then a greater opportunity will be afforded for the incendiary to start a fire which in turn may become a conflagration. Conflagration, being the ultimate objective of incendiary attack, has influenced the design of incendiary munitions, and as control measures have proved successful in the past, just so have changes been made in design to counteract the controls. We will see how this has been done in the latest type of magnesium incendiary. I t must be self evident that in order to start a fire, heat must be brought to the target. This may be accomplished hy use of either the intensive or scatter types of incendiaries, depending upon the particular target, and in the case of the intensive type a "saturation of the target" will tend to exceed the capacity for control by the fire watchers, wardens, and stinrppump squads and force the use of appliances and regular fire departments. The intensive type of incendiary may be illustrated best by the magnesium or thermit bombs, which bring a high intensity of heat directly to one spot and concentrate its energy on the material a t that specific point. On the other hand, phosphorus and thickened gasoline or oil have good application for scattering over a large area containing readily ignitable material, thus employing numerous small burning particles to start a large number of simultaneous fires, with the result that the entire target is set ablaze. Let us now turn our attention to some of these inincendary munitions, particularly the newer types. While much attention has been paid to the 2.2-pound magnesium incendiary bomb and striking success has been obtained with this munition in the past, yet from a practical standpoint it has developed certain defects in attaining its objective. These defects are the ease of control, its lack of penetration power which is necessary to get down to the level where i t can contact inflammable material, and the wartime limitations on magnesium production. Certainly this bomb was a good incendiary to start with but any military weapon becomes obsolete once an effective defense against it has been found. It was soon found that properly organized and trained civilians provided with relatively simple equipment would take care of a shower of these small magnesium bombs spread over a wide area. How then could the effectiveness of this incendiary be enhanced? The answer lies in the fact that if people
could be stopped from putting i t out before a really good fire had been started, the magnesium bomb would still be an effective weapon. We have already referred to the antipersonnel effect of high explosives, and so the first modification of the magnesium bomb was made by including a small explosive charge in the body of some of the bombs. The proportion of bombs thus altered was small and the fire watcher could not distinguish one from another. The Germans evidently supposed that the person attacking the bomb would not take a chance because he would be afraid of all of them and thus would delay all incendiary control. But as the explosive charge was not very heavy, and the proportion of bombs containing explosive was small, the British learned to go after the bomb aggressively, using a shield for protection, and the number of casualties was relatively small. These bombs never seriously deterred the extinguishing of the bombs or accompanying fires. Therefore a new bomb was designed which is the one which we must consider most seriously. This bomb is made of two distinct elements. One element is the magnesium incendiary. The other element is a high explosive unit attached to the magnesium unit. This bomb becomes in effect a dual purpose incendiary and antipersonnel bomb. The total weight of this bomb is five pounds, two of which are due to the magnesium unit and the other three due to the explosive unit. The quantity of high explosive in the latter unit is such that upon detonation a great number of sharp-edged and pointed fragments of the container are projected with great velocity, thus acting as a powerful antipersonnel weapon. On landing the magnesium unit ignites but the explosive charge may go off a t any time up to seven minutes, or possibly even longer, depending upon variations in the delay-action feature. Furthermore, this explosive unit may become detached from the incendiary unit in some manner, so that even though an individual might see and recognize the magnesium unit, yet he would be unable to deiermine whether or not the explosive unit was present in the vicinity. This would be particularly true during blackout conditions and in a darkened room or space occupied by furniture, equipment, and so forth. The greater penetration power of this heavier bomb, influenced by its design, would cause the bomb to go down through ordinary attics into the bedrooms and living quarters of dwellings where much more inflammable material would be located. I am assuming that enough education in respect to housecleaning attics has been accon~plished. We have here a new and important problem to face in controlling fires and the bombs themselves. Are we going to be able to rush in with little or no protection and expect to avoid physical injury or even death while extinguishing the incendiary unit? I hardly think so. Are we going to be able to say to ourselves that only a few of these bombs will have the explosive unit feature? Here again, the answer is no. In attempting any con-
trol measure whatsoever, i t seems only reasonable to base any attempt to extinguish the fire and the incendiary itself on the proposition that potentially all specimens of magnesium bombs are this type and must be handled accordingly. How then are we to solve this problem? The measures employed will be directed toward, first, stopping the spread of fire, and second, the extinguishing of the bomb itself. If a bomb falls in an open area, or on a fire-resistant surface (one which is noncombustible or has been treated with a fire-retarding substance such as whitewash, alginate preparations, etc.) it may be left to burn itself out without further attention. Even in some rooms where the bomb has fallen at a point some distance from inflammable material, say, in the middle of the room, there may be little danger from the incendiary portion during the interval required for the explosive unit to function. But if it is necessary to attempt control, then there are certain steps which should be taken. First of all the individual must have as full protection as possible against the explosive charge. A brick wall three or four inches thick would provide this full protection, but the interior walls of most of our homes and buildings are constructed of lath and plaster, sheetrock, or some similar lightly constructed material. These offer no protection against flying fragments and should not be relied upon to offer protection. However, in congested areas and where buildings and materials are of a highly intlammable nature, in order to prevent any rapid spread of fires it may become necessary to attack the bomb resolutely, employing the best available cover a t hand. How may this be done to the best advantage in extinguishing the fire and incendiary bomb and yet give some protection to the operator? If a prone position is taken by the operator and no more of the body exposed than one hand, a great deal can be accomplished while waiting for the explosive unit to go off and then the usual manner of approaching the magnesium unit may be undertaken. While in this protected position the operator will be able to direct a jet of water around the door frame or in the general direction of the bomb, with the hope of possibly striking the bomb, in addition to wetting down surrounding material. An alternate method, if no stirrup pump or hose is available, would be to throw water from small containers into the room for the same general purpose. There is always a possibility of lack of water pressure if depending on a hose, and so i t is advisable to have several reserve receptacles filled with water for use with the stirrup pump or for dousing from a small container. The detonation of the explosive unit removes the last obstacle in handling the incendiary and any fire resulting therefrom. The usual method of applying a jet of water against the magnesium unit as well as the fire still holds good. The efficiency of the jet of water was determined by
the Chemical Warfare Service in a series of tests performed on the ordinary magnesium incendiary. In these tests i t was found that a magnesium bomh and its accompanying 6re could be extinguished within 22 to 40.5 seconds with a median value of 26 seconds, using quantities of water varying from four to 10 quarts with a median value of five quarts. Furthermore, the operator could stand anywhere from eight to 12 feet from the bomb without apparent danger from the small particles of burning magnesium. The latter were driven away from him by the force of the jet. The question may properly be asked: "If we wait for the explosive to go off, why does not the floor start burning and get beyond control?" Yon must keep in mind that ordinary boards, joists, etc., contain a certain amount of moisture which must be driven off, as well as certain volatile constituents necessary for surface burning. This will use some of the heat generated by the bomb, some of the heat will radiate to the atmosphere, and some will be conducted to the lower layers of the wood. All these dissipations will occur before the main body of the wood has been raised to the kindling temperature. Thus, except for very thin layers of wood and other easily ignited material, the fire should not get too much headway. The use of commercial powders, special scoops, etc., are not recommended. The military does recommend the use of sand as a supplementary extinguishing agent for use when water is not available, and more particularly, after the detonation of the explosive element. Another munition that must be considered is the large (50 kilo) combination explosive-incendiary aerial bomb. This bomh, resembling the usual 110-pound aerial bomb, contains a nose charge of 12 to 15 pounds of high explosive. As it explodes i t ignites and scatters a shower of compact, individual incendiary units, usually magnesium cases filled with thermit. As many as 60 small triangular-shaped incendiary units and six larger units are placed in each bomb. Almost immediately after ejecting the incendiary units, the charge of high explosive in the nose explodes. Technically this is an example of combining both the scatter and intensive incendiary principles in one large bomb. A large number of incendiary units are scattered, each of which bums intensively, and each of which may he extinguished by the ordinary methods. These magnesium bombs are by no means the only
kind of incendiary with which we may have to contend. Other less expensive materials than magnesium may be more readily available to our enemies. Of interest also is the phosphorus-oil bomb consisting of a casing similar to the 110-pound high explosive bomb, but containing only the usual type fuse required to open the casing and scatter the sticky liquid contents. You can readily see how upon exposure to the. air the phosphorus ignites spontaneously and sets fire'-to the oil. The use of heavy oil or solidified gasoline prolongs the burning time and concentrates the heat on any object to which it adheres. Water only is required to extinguish this incendiary material, but keep in mind that upon drying the phosphorus will reignite. Furthermore, any contact of yellow phosphorus with the person will result in severe bums. Thus great care must be exercised in cleaning up residues after the fire has been extinguished, and this may present great difficulty in removing the last traces from crevices and other inaccessible places. The last incendiary which I will discuss is the Japanese bomh weighing about 50 kilos and containing a considerable number of rectangular-shaped rubber-impregnated incendiary pellets and a quantity of thermit. These pellets are scattered widely and start a number of small fires which may be attacked immediately. We must keep in mind that the design of incendiary munitions is by no means standardized; as we devise means of control over those of which we have knowledge, and which are used today, our enemies are endeavoring to counteract our efforts by using new or modified incendiaries. Thus our controls must he constantly revised to meet the new conditions. In conclusion, let me stress the fact that the prevention of fire is our first objective, fire on the scale of a conflagration which possibly would require more equipment than we could muster. Therefore, the control of small fires and incendiaries by the individual or the stirrup-pump squad is the ideal to he sought for. Water still is the main counteragent but the use of sand is justifiable under special conditions. And finally, the presence of the explosive unit in the assembly of some of these magnesium bombs introduces a grave peril to uninstructed personnel. But this is by no means an insurmountable obstacle if each bomb is considered a potential antipersonnel bomb and is approached and handled in the recommended manner.
