Current Techniques in Fighting Aircraft Crash Fires
Latest Methods Developed by Airport Crash Fire Fighters Suggest Procedures for Municipal Fire Services
THE need for equipment and trained firemen fo,r safeguarding lives at airplane crash fires is apparent. Credit must be given the Navy and Army Air Corps, by and with advice from consultant engineers, for development of apparatus and equipment presently used. The evolution of such dates back about ten years, the major part since the war began.
Fires resulting from airplane crashes are predominantly gasoline fires and must be treated as such. Their control has been handicapped by having to transport all extinguishing agents to the crash, consequently equipment has been designed to get the greatest value from extinguishants carried. Municipal departments will not have this difficulty, at crashes occurring within its city limits, because it is to be assumed that adequate quantities of water will be available.
Extinguishing agents presently used are water, carbon dioxide, foam—dry powder to a limited extent—and carbon tetrachloride. The latter is of little value at a crash fire, being better for motor fires. The relative values of the others are about equal. There are certain conditions when carbon dioxide is preferable, but generally dependence is placed on water, either as high pressure fog, low pressure fog, or foam. Pump pressures of from 500 to 700 pounds are used for high pressure fog, which results in a much finer and more effective spray for controlling petroleum fires. The large quantity of carbon dioxide carried on the Cardox truck (6,000 pounds) is equally good, but smaller quantities (300 pounds or less) have little value.
Apparatus and Equipment
A brief description of existing crash equipment, pump capacities, and quantities of extinguishing agents carried, and a delineation of fire fighting methods known to be effective, will better enable the Municipal Department to plan the use of equipment they now have for the control of airplane crash fire.
The several classes of crash fire fighting equipment are outlined in the accompanying table.
Of the foregoing seven pieces of apparatus only three use carbon dioxide, either wholly or in part; all others rely on water in the form of fog or foam for extinguishment. The class 110 is essentially a foam producing unit, but carries 200 pounds of carbon dioxide. The classes 125 and 135 are primarily high pressure fog trucks, however, by mixing foam solution with the water, either foam or high pressure foam fog may be utilized.
Foam produced by crash equipment is of the mechanical type, and differs from chemical foam in that the bubbles are filled with air instead of carbon dioxide.
This is accomplished in one case by mixing a foam fixing solution with the water in the tank, and pumping through special nozzles wherein air is introduced, forming foam. In the other method plain water is pumped through the delivery lines, and by means of a pick-up tube the foam solution is mixed with air at the nozzle. This is known as the Hip Pack Foam Producing Unit, and will hereinafter be referred to as the “Hip Pack.”
Most firemen are familiar with the application of foam for extinguishment,and many have had considerable experience with the use of fog both in general fire fighting and in controlling petroleum fires. It is believed, howevey, that a full understanding of how and why water fog extinguishes gasoline fires will enable the fire fighter to use it more efficiently.
Current Apparatus Used to Fight Crash Fires
Water fog extinguishes fire by absorption of heat and by unping or sepa- rating flame from fuel. The maximum extinguishing value of water is obtained when fully converted into steam, therefore the finer the spray the more steam produced, with resultant efficiency. Comparing two spray streams delivering equal amounts of water, the droplets in the first being just one-half the diameter of those in the second, it will be found that the water surface of the former is exactly twice that of the latter. Because of the greatey water surface of the finer spray the rate of heat absorption is relatively faster. Although the heat absorbed by two equal quantities of water should be the same, the first stream is much more effective than the second. Why? Because more teatcr has been converted into steam, and in less time. The rate of heat absorption by water is proportional to the surface exposed; hence the greatey the surface the faster the absorption.
Applying Spray and Fog
The second extinguishing effect of water fog on burning gasoline is the application and advancement of a fog-front, whereby the flames are wiped off, or separated from the burning liquid. In most cases the fog stream should be applied and advanced laterally instead of head on, because a wider front is thus presented. Figures 1 A and B will illustrate :
In Fig. 1 A below the fog nozzle should be adjusted so the spray will reach entirely across the burning liquid, then advanced slowly and steadily to the right. It should be held horizontally about 14 inches above the burning surface, so that the fog-front touches and spans the burning area. Figure 2 illustrates the elevation of the nozzle.
Presenting the fog stream head on as in Fig. 1 B is not so good because the fog-front is not broad enough, and it is more difficult to prevent flash backs.
If gasoline spills over a large area one fog nozzle will be entirely inadequate.
How to use two fog nozzles is shown in Figure 3.
Station the two fog nozzles so that the fog styeams meet at the edge of the fire at an angle of about 90° forming a wedge; then advance until the fire has separated in the center, after which the fog streams should be rotated outward sweeping the flame from the fuel. This procedure originated from the necessity for opening a path through which rescues could be made, but has proven quite as effective for extinguishment.
For gasoline spills of considerable magnitude not less than four fog streams are necessary for effective results. This ground plan, Fig. 4, indicates the relative positions of the four nozzles.
In the evolution, Fig. 4, Company No. 1, places the first two streams in service as indicated in Fig. 3. Company No. 2 then places the second two streams, parallel with, about three feet outside of, and four or five feet to the reay of the first two streams. The secondary streams thus provide protection against heat for the primary nozzle men. All streams should be held horizontally at the 14-16″ level, until the rescue men are ready to enter the rescue path. The inside streams should then be trained to the right and left of the rescue men between the hip and shoulder, while the outside streams aye held at the 14-16″ level. To effect extinguishment, inside and outside streams should be maintained parallel and moved slowly outward until flames are swept from the burning surface. Should flash backs occur raise the streams, swing back to center of burning area, lower to proper position, and proceed as before.
Beware of Flash Backs
Due to the high volatility of gasoline, flash backs are apt to occur, and every precautionary measure should be taken to prevent them. Foam applied immediately behind the fog streams will serve that purpose by blanketing unburned fuel. Any type of foam producing equipment will suffice. Even the 2 1/2gallon foam extinguisher, if several are available, can be used to cover a large surface. The dry powdey foam generator is effective if it can be placed in service without delay. The hip pack foam unit is most adaptable for this purpose. While few are now in the possession of City Fire Departments it is believed they will soon be available! The proper application of foam is shown in ground plan Fig. 5.
The foregoing illustration indicates the foam stream applied on the ground at the point P just outside the burning area. Thus the foam flows over the fuel exposed.
One might wonder why foam alone is not used for the control of airplane crash fires. Foam applied as a blanket absorbs little heat, and as at many crashes, there is a need for effecting rescues, water fog is used for protecting both rescuers and the rescued. It will be noted in Fig. 3 that a pathway completely filled with water fog has been opened through the fire, through which rescues may be accomplished with comparative safety. The primary objective is to open and hold this rescue path until rescues have been made, after which extinguishment is completed. Then, too. water fog is useful for cooling and excluding heat from fuselage where victims may be trapped.
The airplane crash Company or crew is preferably composed of six men. Their duties and the number of their working positions, as shown in Fig. 6. are as follows: Captain or Crew Chief, No. 1; Pump Operator, No. 2; Nozzle Men, Nos. 3 and 4; Rescue Men, Nos. 5 and 6.
Note that all nozzle men take position on the inside of their respective lines. These men are subject to more punishment from heat than other crew members, and the necessity for proper protective clothing is apparent. In the foregoing illustration the rescue men are in position to enter the rescue path. The Captain remains where all operations can be properly supervised. The crash kit, containing tools for forcible entry and the release of victims, has been opened and conveniently placed by the rescue men.
In the matter of protective clothing, the asbestos suit has long been in use for fighting major oil field fires, but for crash fire fighting it has not proved so practical. Space will not permit a full discussion of the relative values of the asbestos suit versus bunker clothing. It will suffice to say that most crash crews prefer regulation bunk out suits, gloves, and helmets. The rescue men must be provided other protection for head, face and neck, the most popular being an asbestos hood, or cape, constructed to fit over helmet and drop below the shoulders. One such hood is now being manufactured under government specifications for use at army air fields, and no doubt one similar will soon be available for municipal use.
The foregoing dissertation will serve to acquaint the municipal fireman with the fire fighting methods and equipment that have proven most effective at airplane crashes. Howevey, these must not be taken as the last word in crash fire fighting. Much is yet to be learned, and the fire fighter, who can think for himself will contribute much to that phase of fire department work.
(To be concluded in the next issue)
Editor’s Note: Mr. Taplin. author of this article, was formerly Chief of the Blackwell, Okla., Fire Department and Secretary of the Southwestern Association of Fire Chiefs. Later he was connected with an airport fire force. The foregoing article is compiled in part from his address before the last session of the New Mexico Fire School. The opinions expressed are naturally Mr. Taplin’s own and do not necessarily represent those of the publishers of this journal.