TM 1-411, Airplane Hydraulic Systems and Miscellaneous Equipment: 6 - Fire Extinguishing Equipment

SECTION VI: FIRE-EXTINGUISHING EQUIPMENT

40. General.-a. Fire extinguishers used in aircraft are of two general types: the fixed type fire extinguisher which is a built-in system employing carbon dioxide, and the portable or hand type fire extinguisher using either carbon dioxide or carbon tetrachloride.

b. The carbon dioxide fire extinguishers are particularly effective in combating gasoline or oil fires. However, if fabric, wood, etc., are involved, the carbon tetrachloride extinguishers may be used alone or in conjunction with the carbon dioxide extinguisher.

c. The extinguishing equipment carried on aircraft is adequate for combating incipient fires only, and the extinguishers, regardless of type, should accordingly be put into action as soon as possible after the fire starts. The following instructions are included as a guide in fighting fires in airplanes:

(1) Engine, fuel tank, and amphibian hull fires.-If the airplane is equipped with a built-in fire extinguishing system, set the distributor valve to the proper position as soon as the location of the fire has been determined and pull the release handle. In the case of an engine fire, first shut off the supply of gasoline to the engine and then fully open the throttle. Open all emergency exits.

(2) Wing fires.-Turn all switches controlling landing or navigation lights to the OFF position. Open emergency exits.

(3) Cabin fires.-Close all windows and ventilators. Use hand fire extinguisher on the fire. When using the quart carbon tetrachloride hand fire extinguisher in confined spaces, stand as far from the fire as possible. The effective range of the extinguisher is approximately 30 feet. Immediately after using the extinguisher, open windows and ventilators. In the case of  an electrical fire, turn the main switches off, and in the case of a leaking fuel or oil line, shut off the valves.

d. While carbon dioxide (CO₂) is a nonpoisonous gas and breathing it will not adversely affect a human being either at the time it is inhaled or afterward, carbon tetrachloride is a volatile fluid, the gases of which when inhaled in large amounts act as an anesthetic, causing drowsiness, dizziness, headache, excitement, anesthesia, and sleep. Any one or all of these symptoms may occur. In case any odor of carbon tetrachloride is detected while flying, an investigation to determine its source should immediately be made. If it is found that a fire extinguisher is leaking, it should be corrected at once. When sprayed on a. fire, carbon tetrachloride produces phosgene. The inhalation of even a small amount under such conditions may produce harmful effects and, if a sufficient quantity is taken into the lungs, the results may be fatal. Breathing the fumes when using the fluid on a fire should therefore be avoided.

41. Fixed type carbon dioxide.-a. The purpose of this fire extinguisher is to provide a means of flooding an engine compartment, amphibian hull, or gasoline-tank compartment with CO₂ gas in case of fire in those regions. A distributing valve mounted within easy reach of the pilot is set to direct the gas to the desired location, and a pull handle is operated to release  the gas from the cylinder. The operating controls of this equipment are clearly marked to indicate, their correct use.

b. Fixed-type CO₂ fire extinguishers are supplied under three different designations: single-discharge line, two-discharge line, and three-discharge line. These are used on single-, twin- and three-engine airplanes respectively. The single-engine, fixed-type fire-extinguisher system consists of the following elements: Pull handle; CO₂ cylinder; release valve; supply tubing; distributing tubing; and in some cases, carburetor nozzle. Schematic drawings of this system for the air-cooled and liquid-cooled engines are shown in figures 38 and 39. The multi-engine installations have the same component units as the single-engine installation with additional tubing, carburetor nozzles, a distributing valve, and a cylinder of larger capacity. A schematic drawing of the three-engine installation is shown in figure 40.

FIGURE 38.-Tubing installation, air-cooled engine.

FIGURE 39-Tubing installation, liquid-cooled engine.

FIGURE 40.-Schematic diagram, multiple-engine installation.

c. The control panel with handle is mounted in the cockpit or the pilot's cabin where it is easily accessible to the members of the crew. Operating instructions are printed on the panel and in the case of multi-engine systems the settings for the distributing valve are also noted.

d. The type CO₂ cylinder used is that specified in table III for the particular fixed-type fire extinguisher being used. The mounting position of the cylinder is as follows:

(1) If equipped with a straight syphon tube the cylinder is mounted vertically to the thrust line, but may be tilted 30° forward or aft of this position.

(2) If equipped with a short flexible syphon tube the cylinder is mounted parallel with the thrust line with the valve end aft, but may be tilted 30° below this position at the valve end.

e. Fixed type fire extinguisher systems employ either the cutter type valve or the quick release type valve on the CO₂ cylinder. The cutter type valve assembly (fig. 41) is screwed directly onto the body bushing and consists briefly of the cutter valve body which houses the piston cutter and the piston actuating spring. The upper portion of the cutter extends outside of the cutter valve body. The entire piston is bored out hollow from the cutter end to a short distance beyond its extension outside of the cutter valve body. At this point it terminates in four relief ports, which vent the gas to the atmosphere on a premature discharge. A red indicator is fastened to the upper end of the piston and a celluloid cap is placed over this indicator. This cap is such that when the cutter valve is in its normal set position, the red indicator is covered from sight. Upon operation of the cutter valve, the piston travels downward bringing the red indicator into view, thereby giving a visual indication that the cylinder has been discharged. Should an abnormal temperature cause the safety disk to burst, the gas would travel up through the tubular cutter, then through the bore in the piston and out the relief ports, which in turn would burst the celluloid cap, allowing the gas to escape into the atmosphere through this channel rather than through the discharge line and distributing system to the engine. In this case the red indicator would be exposed to view denoting that the cylinder had lost its charge. The control handle in the cockpit is connected by means of flexible cable in tubing to the manual release lever on the cutter valve. The manual release lever can be rotated about 15° after which continued rotation allows the camshaft in the cutter valve body to rotate freely. The piston spring then forces the piston down, thereby cutting the disk, which releases the gas. When the piston is forced down by the spring, the relief ports fall below the reset nut into the spring chamber, which causes the gas to pass through the tubular cutter into the bore of the piston, thence through the relief ports into the spring chamber, and thence to the supply tubing.

f. The quick release type valve consists of a valve body containing a retainer assembly which includes an operating handle with a notched cam and hollow valve stem. Figure 42 shows the valve assembly

FIGURE 41.-Cutter type valve.

FIGURE 42.-Quick release type valve.

With the retainer screwed down and with the handle down, the valve is held on its seat by the cam in the operating handle. When the handle is raised, as shown in the middle view, the cam rotates so that the gas pressure on the valve seat can force the valve stem into the notch in the cam and the CO₂ gas is released through the syphon tube and the hollow valve stem to the nozzle of the valve and thence to the supply tubing. To reset the valve the retainer must be backed off to a position shown on the right view of figure 42 and the handle placed in the down position before the valve can be reseated. The retainer assembly is then screwed down until the valve stem is on the seat.

g. The distributor cock used on the multi-engine fixed type extinguisher directs the output of the CO₂ cylinder to the particular engine or compartment for which the setting is made on the control panel. The valve itself is a three- or four-port rotor type selector valve mounted on the rear of the control panel.

h. The supply tubing is of aluminum alloy having an outside diameter of 1/2 inch and a 0.032-inch wall thickness. The fittings are also of aluminum alloy. Bends in the supply-line tubing are limited to radii greater than three times the outside diameter of the tubing or in this case 1 1/2 inches.

i. The tubing and fittings of the distributing lines are similar to the above, except that the tubing is drilled with small perforations for the proper discharge and distribution of the CO₂ gas to the areas being protected. The distributing system for the air-cooled and liquid-cooled engines are shown respectively in figures 38 and 39, the arrows indicating the discharge of the gas through the perforations. On some installations, additional protection is provided for the carburetor by a circular length of perforated tubing running from the main engine system around the carburetor, or a direct line running to a carburetor nozzle located in the carburetor intake just below the butterfly valve. If the engine is mounted in a nacelle, added protection is sometimes furnished by running two lines from the main system to the rear end of the nacelle.

j. Operation of the fixed-type fire extinguisher in the case of engine installation is accomplished by pulling the control handle on the control panel. Through the control cable this actuates the lever on the cylinder-release valve and the CO₂ gas in a liquid state is forced under cylinder pressure through the supply tubing, and thence to the distributing system tubing. Vaporization of the liquid occurs as the CO₂ passes through the perforations in this tubing and streams of carbon dioxide gas are forced into the engine region. In the case of the multi-engine installations, it is necessary to first set the distributing cock to the proper setting on the control panel and then pull the control handle, which performs the same function as described above.

k. In case the release valve cutter becomes dull or deformed it is replaced, never sharpened, as this might shorten it to a degree that it could not reach the sealing disk. In case the perforations in the distributor tubing become clogged, the holes are opened up and a stream of compressed air is directed through the tubing from the inside. The release valve control cable is packed in graphite grease.

FIGURE 43-Portable type carbon dioxide fire extinguisher.

42. Portable type carbon dioxide.-a. This CO, extinguisher (fig. 43) unlike the fixed type previously described may be used to combat fires in any part of the airplane.

b. The component parts of this extinguisher are as follows:

(1) A CO₂ cylinder having the capacity specified in table III for this extinguisher, and equipped with a carrying handle.

(2) A quick release type valve Of a design similar to that described and illustrated in the previous discussion of the fixed type CO₂ fire extinguisher.

(3) A flexible hose equipped with threaded fittings for connection to the valve outlet and conical horn.

(4) A conical horn equipped with wooden handle and containing a discharge orifice which serves to restrain the liquid CO₂.

 c. The operation of the extinguisher is accomplished by merely pulling up the release handle. Since the released carbon dioxide is at an extremely low temperature, care must be taken in operating this type of extinguisher not to touch the conical horn.

43. Portable type carbon tetrachloride.-a. This extinguisher (fig. 44) is a 1-quart hand-operated type which expels the liquid by air pressure. Pressure to discharge the liquid is obtained by means of a hand-operated air pump forming an integral part of the extinguisher. The extinguisher employs carbon tetrachloride (CCL₄) as the extinguishing medium. This chemical is a nonconductor of electricity and may be safely used on fires where electric current is involved.

b. The housing of this fire extinguisher is a brass cylinder which contains a hand pump unit incorporating a check valve. The unit is 13 1/2 inches high and 3 inches in diameter rind weighs 7 pounds fully charged. The mechanism is such that the pressure compounds and continuous pumping are unnecessary and the ease with which the pump may be worked enables the operator to direct the stream with greater efficiency.

c. This type fire extinguisher may be mounted either horizontally or vertically. When mounted in a vertical position, the nozzle or discharge end is at the bottom. Those that. are accessible both from within aircraft and from the ground are, wherever possible, located on the side of the aircraft normally approached for entrance, that is, on which steps, doors, etc., are installed.

d. The life, of an extinguisher can be materially lengthened if it is kept filled, wiped free of dust, dirt, and grime; periodic inspections are made in order to insure that the pump action has not been impaired by internal corrosion, and that each extinguisher will function properly when required in an emergency. These should include sufficient operation of the pump to determine its serviceability. The contents are discharged into a clean glass container. If the liquid is milky and brownish in color it is usually due to the use of impure liquid or the introduction of water which has caused corrosion. If the liquid is clean and clear it may be returned to the extinguisher by removing the filler cap and pouring it back with the aid of a small clean funnel.

FIGURE 44-Portable type carbon tetrachloride extinguisher.

When one full quart is returned the filler cap is replaced and tightened down as the escape of air pressure around the filler cap will reduce the pressure which expels the liquid onto the fire. If the pump works hard a few drops of neat's-foot oil dropped on the piston rod will find its way down to the leather cup on the piston and soften and restore its life. In case the pump shaft is stained with corrosion, it is cleaned with metal polish and then coated with soft cup grease.