Gas Masks and Breathing Apparatus
44-507-Hose Masks for Damage-Control Purposes
S93-(6) (688), EN28/A2-11, 22 April 1944
ACTION: ALL FORCE AND TYPE COMMANDERS
(Enc.: (A) Photograph of ND Mark III Gas Mask Modified to a Hose Mask.)
1.The Bureau has received recommendations from the Fleet Maintenance Officer, Commander Service Force, Pacific Fleet, and various ships for gas masks of the "hose" or "air-line" type for entering voids such as those containing gasoline vapors and spaces with extremely small access hatches, etc., in which the use of the present oxygen rescue breathing apparatus would be unsatisfactory.
2.Hose masks or air-line masks, as they are sometimes called, usually consist of a gas mask facepiece with adjustable head harness and a length of air hose, one end of which is connected to the facepiece and the other end terminating in fresh air or connected to a compressed-air supply, such as a compressed-air cylinder with intervening air regulator, or to an air pump with intervening air reservoir.
3.The Bureau proposes to supplement the oxygen rescue breathing apparatus with hose masks which will be carried on board as permanent equipment in damage-control repair lockers on the basis of two for each locker.
4.An experimental lot of hose masks fitted with 100 feet of air hose, air regulator, pressure gage, quickly acting connection for connecting the hose to a compressed-air supply, and a safety belt and life line are being shipped to the Fleet Maintenance Officer, Commander Service Force, Pacific Fleet, for trial use to determine the suitability of the mask fittings as standard equipment. If these fittings are found satisfactory, the number of sets required will be procured and furnished each ship for converting the facepieces of standard ND Mark III or Mark IV service gas masks into hose masks. In the meantime, the Bureau has no objection to ships improvising hose masks from the facepieces of the standard ND Mark III and Mark IV service gas mask. This may be accomplished by the ship's force as follows:
(a)Tear off the friction tape at each end of the canister, cut the binding wires and pull the corrugated rubber tubes from the ends of the canister.
(b)Provide an air manifold as illustrated in enclosure (A), figure 1. This manifold may be made of 1" low-pressure seamless brass tubing. Drill two ¼" holes, one near each end, as shown, to allow for free flow of air in case the corrugated rubber tubing, through accident or otherwise, is pressed against and closes the end openings of the manifold.
(c)To each end of the manifold, silver-solder a brass disk leaving a ½" diameter hole in the middle and an out-side diameter 1/8" greater than the outside diameter of the end of the manifold. The disk should be accurately centered and when so installed it provides a flange or bead over which the elbow of the corrugated breathing tube is drawn.
(d)In the center of the manifold and in direct line with the two ¼" diameter holes, referred to under (b) above, drill a hole of sufficient diameter to permit the insertion of the end of a regular oxygen-hose coupling of sufficient size to take a 5/16" inside diameter or larger air hose. Silver-solder this connection securely in place.
(e)Apply three coats of No. 4 steel and rubber cement to the manifold, taking care to prevent its entrance into the air holes. Allow the cement to dry between coats. Draw the elbow of the corrugated breathing tubes over the ends of the manifold, taking care that the wall of the elbow clears the end and side air holes. Cover the end of each breathing tube with several turns of friction tape. Seize the ends of the breathing tubes to the manifold with three turns of small-gage brass or copper wire over the friction tape. Apply several coats of cement and cover entire manifold with a layer of rubber tape, followed by one coat of glyptal (electric insulating varnish). The complete air manifold assembly is illustrated in enclosure (A), figure 2.
(f)From a low-pressure ¼" globe valve (figure 4 of enclosure (A)), remove the valve stem, seat, and gland packing. Silver-solder single end oxygen hose couplings to the valve supply and exhaust openings. The couplings are shown in figure 6, enclosure (A). They should be of sufficient size to take 5/16" inside diameter or larger air hose. This is the air control valve. Silver-solder the globe of the valve to a 3" x 2" piece of brass plate (approximately 18 gage) in a position that when installed on a body belt, the intake opening will point to the rear, the valve stem to the front, and the exhaust opening upward. Reassemble the valve and make suitable provision for fastening the brass plate to the wearer's belt.
(g)Attach a short length of 5/16" inside diameter or larger air or oxygen hose from the air mask to the control valve and one or two 50' lengths of the same size hose as may be required from the control valve to the air supply. The hose should not be less than 5/16" inside diameter.
(h)The head harness pad of ND Mark III and Mark IV gas masks is fitted with a wire bail from which the canister is suspended. This bail, by wiring it to the manifold as shown in figure 2, enclosure (A), can be likewise used to support the manifold from the head pad.
(i)Air supply should preferably be from cylinders containing compressed air or from the low-pressure air lines of ships, reduced to proper operating pressures by means of a two-stage regulator. Tests have indicated that a standard 200 cu. ft. cylinder, fully charged with compressed air, will serve one man from one and one-half hours, if the pressure in the facepiece is maintained at a pressure just slightly above the pressure of the surrounding air. As an alternative, the air supply may be derived from compressors or hand-operated pumps provided the intake of same is located in pure air and the lubricants used are not toxic or obnoxious, and also that an air reservoir of at least 1 cu. Ft. capacity be interposed in the air line between the source of supply of air and the wearer. The latter is to insure a constant flow of air by eliminating the pulsations in air flow otherwise induced by the compressors or pumps. Hand-operated pumps, such as used with shallow-water diving outfits, have been found satisfactory for this purpose.
(j)Wearers of the above gas masks should be equipped with life lines made of rope or small wire cable secured to a belt. The latter can be made up on board. It should be of sufficient strength to support a man of average weight with at least a 50-percent factor of safety. The life line should be loosely lashed to the hose to reduce the possibility of fouling.
5.The Bureau desires to emphasize the following characteristics of these masks:
(a)It is necessary that a continuous positive pressure be maintained in the facepiece at all times.
(b)The maximum length of hose which can be used without a pump or compressed air bank is 25' with a minimum inside diameter of 1". Longer lengths may be used with a pump.
(c)It is possible for the space in which the pump is located to become contaminated with smoke or gas, in which case the wearer of the mask would be supplied with contaminated air.
(d)The trailing hose is susceptible to burning if there is any intervening flame and to fouling where there is wreckage or other structural obstruction. These conditions could result in stoppage of air and necessitating the removal of the mask by the wearer.
6.These converted masks are not intended for use under conditions where the pressure of the surrounding medium is greater than atmospheric pressure. Where such masks are desired for shallow-water diving, conversion should be in accordance with the Bureau's letter S94-3(1) (88OT), EN28/A2-11, of 24 August 1943 appearing as Article R-1375 of Navy Department Bulletin of 1 September 1943, Vol. III, No.5. [N.D. Bul. Cum. Ed. 1943, p.1118.]-BuShips. W.F. Christmas.
S94-3-(1) (880T), EN28/A2-11, 24 August 1943
ACTION: ALL SHIPS AND STATIONS
(Ref.: (a) BuShips ltr. S94-3-(2) (8688) EN28/A2-11, to all Ships and Stations dated 12 November 1942. (b) CO USS Helena ltr. CL50/S94(07), dated 12 January 1943. (c) CO USS Curtiss ltr. AV4/S94 serial 021, dated 6 April 1943. (d) Comdt. NYd, PH S94/S77 serial 104764 of 2/10/43 to BuShips.)
(Enc.: (A) Arrangement of Connection of Gas Mask. (B) Side View of the Converted Gas Mask.)
1.In order to provide a shallow-water diving outfit that would overcome the limitations of the helmet outfit, a face mask, described in reference (a), was adopted for shallow-water diving. With the new mask, a diver is able to assume any position and accomplish work that could not be done with the helmet. By adding the correct amount of weights to give proper buoyancy, the diver can attain almost complete freedom of motion under the water.
2.Due to the delay necessarily caused by changing to a new outfit, it was impossible, temporarily, to furnish the new shallow-water outfits to a great number of activities requiring them. Therefore, various activities, as reported in references (b) to (d), improvised diving outfits from service gas masks ND-MkIII or IV. These activities have reported obtaining very satisfactory results with the converted masks. For those activities not familiar with the use of the gas mask as a diving mask, the following method of making the conversion is recommended by the Bureau.
(a)Double rubber flutter valve back on itself and seize tightly with tape to prevent air from escaping through it. It should be noted that air escapes from the mask around the periphery.
(b)Unscrew diaphragm retainer ring and remove diaphragm. Insert a solid blank disc of sheet metal, and make watertight by means of a rubber gasket under the disc; screw retainer ring on tightly. It is advisable to wind tape around retainer ring to insure a watertight connection.
(c)Remove canister, being careful not to damage the gas-mask tubes.
(d)Connect the gas-mask tubes with a piece of brass tubing, in the form of a "T". Secure the brass tubing in gas-mask tubes, using gasket cement and hose clamp or some other suitable means.
(e)Attach to the leg of the "T", a nonreturn valve that will open at a low pressure (about 8 ounces) and have an orifice of sufficient area of flow corresponding to 5/16" diameter hose. This is a minimum requirement. There should be no leakage when the external pressure falls below the pressure in the mask.
(f)Make the necessary adapters to connect the diver's air-control valve (globe valve is satisfactory) to a standard 5/16" oxygen hose fitting. To the discharge side of the globe valve secure a 3-foot length of oxygen hose leading to the nonreturn valve on the "T" connection. To the inlet side, attach a 50-foot length of standard oxygen welding hose. The globe valve should be attached to the cartridge belt to prevent sudden strains jerking the mask off.
(g)When using the shallow-water pump, a volume tank not less than 1/2 cubic foot should be used. Attach one end of 50-foot length of hose to the discharge side of the tank. To inlet side of the tank, connect a suitable length of hose to the pump.
(h)A life line made of 21-thread manila rope should always be secured to the diver. The line should be secured to the air hose as shown in the enclosures, and should be readily detachable from the diver in the event of fouling.
This assembly will provide the greatest amount of freedom, and generally conforms to the standard practice of hose, life line, and control valve arrangement.
3.In some instances, masks have been used to depths beyond what would normally be considered shallow water. In this connection, the Bureau does not recommend the use of the shallow-water diving mask below 36 feet, except in special cases, and then only by trained divers. Diving should not be undertaken by untrained personnel, except under the supervision of a diving officer or trained divers designated by the diving officer, and then the depth of dive should not exceed 36 feet. The basic requirement of all diving is that sufficient air be supplied the diver. Due notice must be taken of the dangers involved, and good judgment is a requisite if diving is to be carried on with any degree of safety. If diving is carried on at depths below 36 feet, the same decompression must be given as for similar dives of the dressed diver. Ascent from depths of 36 feet or less may be made up the ascending line, or by stage hoisted from the surface at a rate not greater than 50 feet per minute. Divers are cautions against throwing off the mask and swimming to the surface. However, in case the mask is accidentally pulled off the face, the diver should freely vent air from the lungs during the ascent.
4.In addition to diving on air, pure oxygen may be used as a breathing medium up to 40 feet. However, pure oxygen should not be used to greater depths, due to the toxic effect of oxygen. Individual tolerances vary greatly, and individual susceptibility should be determined.
5.The primary reason for the distinctions between shallow-water and deep-sea diving outfits is the physical danger involved in using shallow-water equipment, and not the physiological dangers, which are the same regardless of the type of equipment used. Shallow-water outfits are furnished to activities that do not have specific diving duties assigned, but have small and necessary jobs to accomplish at infrequent intervals. This equipment is furnished for work of a nature that can more easily and just as safely be accomplished by using a shallow-water outfit, such as clearing a hawser from a ship's screw, cleaning strainers and scuppers, cleaning the ship's bottom, searching for objects lost in comparatively shallow and warm water. However, where more extensive operations are concerned, such as battle-damage repair, salvage, or any work that necessitates the diver working inside the ship or in or around where there is extensive damage, a deep-sea diving outfit should be used. When diving in areas where there is extensive damage, or where there are wreckage projections, the diver wearing a gas mask or standard mask is very likely to sustain serious physical injuries, particularly about the head. Under such conditions, a diver in either is apt to become fouled in some manner. However, the possibility of the diver losing his air supply is less likely in a full dress than with only a mask that can be readily pulled off the face.
6.It should be noted that while diving with a mask of any type offers greater freedom and permits more work to be accomplished, there are certain hazards that must be guarded against that are not encountered when using the shallow-water helmet. It should not be assumed that, because of the flexity of the mask, it is impossible to get a squeeze. In the ideal case, where the mask would be flexible enough to completely collapse against the face when the air pressure is lost, there would be little likelihood of the diver's face being squeezed. However, this is not the case with either the standard mask or the gas mask, which are not completely collapsible. In order to eliminate the possibility of getting a face squeeze, all masks should be equipped with the nonreturn or check valve on the supply line as specified in paragraph 2(e) at the same or lower level than the mask, since squeeze resulting in rupture of the blood vessels of eyes, nose and lungs, etc., can occur at any time that the pressure in the mask falls below the surrounding water pressure.
7.When diving in cold water the objective must be to reduce the circulation of water in the vicinity of the skin. This can be accomplished to some extent by wearing heavy underwear, or to a lesser extent by using a coating of heavy grease.
8.While very satisfactory results have been obtained with the use of the gas mask, it should be remembered that the gas-mask diving outfit is an improvisation, and the mask part of the equipment being used has been furnished for a definite purpose other than diving. However, the Bureau does consider the gas mask to be a very satisfactory substitute for the standard mask.-- BuShips.P.W. Hains.
How does an OBA work?
The question is not academic. The right answer might save your life.
Accident reports following the fires aboard the carriers USS Oriskany (CVA-34) and Forrestal (CVA-59) maintain that there were some among the would-be firefighters who could not enter smoke-filled compartments for the simple reason that they did not know how to use this piece of firefighting gear.
The number of Navymen thus ill-prepared is not known. But it really doesn't matter.
One is too many.
This article is meant for you, if you:
-Have not put on an OBA and activated a canister within the
last few years.
-Do not know where the OBAs are stowed aboard your ship.
-Do not know why a gas mask and an OBA cannot be used interchangeably.
If you fit into one or more of these categories, perhaps the information that follows will jog your memory. It will not, of course, substitute for practice with an actual OBA.
The Oxygen Breathing Apparatus is designed to circulate air repeatedly through a closed system. During the air's round trip through the OBA, two important things happen to it. First, the carbon dioxide is removed from the exhaled breath; then oxygen is chemically generated, and added to the air which is to be inhaled.
Unlike a gas mask, which continually brings in outside air and filters out dangerous particles, the OBA keeps circulating the same air over and over again. The fact that outside air is inhaled through the gas mask's filter nullifies its use in firefighting. The air in the vicinity is rather short on oxygen. A gas mask does not generate oxygen. An OBA does.
The OBA's essential components are an airtight facemask, an exhalation tube into which the wearer breathes, a removable canister containing the oxygen-producing chemicals, a breathing bag which stores the rejuvenated air and cools it, and an inhalation tube leading back to the facemask.
The OBA facemask is made of rubber, with plastic eyepieces, a speaking diaphragm, and a rubber mouthpiece. A short tube just below the speaking diaphragm contains the inhalation and exhalation tubes, and check valves for each.
The breathing bag, which must be filled before the OBA can be used, collects air and retains it long enough for it to cool.
The most important feature of the OBA, of course, is the canister containing the oxygen-producing chemicals.
The canister consists of five layers of chemicals separated by wire mesh screens. When moisture and carbon dioxide from the wearer's breath enter the chemicals, oxygen is released and the carbon dioxide is absorbed.
The canister has a lanyard on the bottom which, when pulled, fires off a fast-burning chemical which produces pure oxygen as it burns.
Called a "candle," this chemical cake produces enough oxygen to last from two to four minutes. While the OBA-wearer is breathing this supply of oxygen, his exhaled breath starts the chemicals in the main portion of the canister working.
For a full understanding of the principle of the OBA, it might be helpful to trace the course the air takes within the closed system. We'll follow the air from the time it is exhaled from the lungs. The air flows down through the exhalation tube to the canister of chemicals, where it is led through a central pipe to the bottom of the canister.
The air then rises through the chemicals in the canister, losing carbon dioxide and moisture, and gathering oxygen as it goes.
The air travels up into the breathing bag, where it is stored until the wearer inhales it. This delay gives the heated air time to cool.
The most obvious thing you must know about the OBA, of course, is where to find one when you need it. Copious knowledge about its internal workings will do you little good if you can't find one in an emergency.
OBAs are stored in the damage control repair station, which are also called repair lockers, and in various other places throughout the ship. A destroyer usually has three such storage facilities, while larger ships have correspondingly larger numbers of them. If you do not already know where they are located aboard your ship, you should make it a point to find out.
Before you can use the OBA, there are certain steps that you must take to get it activated. The process sounds long and involved, but actually takes only a few practice sessions before it becomes second nature to a potential firefighter.
First, of course, you have to put on the OBA and tighten all straps so that you have a snug but comfortable fit. Now you're ready to insert the all-important canister.
Before putting the canister in place, you first must remove the metal protective cap to expose the metallic-foil seal in the neck. This is done by pulling the metal tab straight across the top of the cap and down, as if you were opening a can of your favorite beverage.
In using a quick-starting canister, you remove the rectangular cover on the bottom of the canister and let it dangle from the lanyard. The swinging bail which holds the canister in place has a handwheel. Loosen it, and swing the bail outward. Now you can insert the canister into the canister guard.
There is a "canister stop" near the top of the canister guard to keep the canister from going all the way up and puncturing the seal prematurely. When the canister hits the stop, swing the bail back in place under the canister and turn the handwheel enough to hold the canister in.
To activate the canister, push the canister stop in as far as it will go, then turn the handwheel until the canister travels up and seats against the main valve.
When you have put the facemask on and adjusted the straps to fit your head, you are ready to get the chemical reaction started in the canister.
The quick-starting canister is easy to get started, as its name implies. Pull the lanyard on the bottom of the canister with a steady pull away from the body. This removes the cotter pin from the candle and fires it off.
Starting the candle may be accompanied by a slight amount of harmless smoke. The breathing bag will immediately fill with oxygen and you may proceed with your work. While the candle is providing oxygen to the breathing bag, it might get too ambitious and overfill your bag. In this case, vent the bag by depressing the starter valve (on the cross tube just below the facepiece) and letting some oxygen seep out.
The length of time your canister will last will vary according to the amount of work you are doing. So that you can tell how much time is left in the chemicals in your canister, a timing device is provided as a part of the apparatus. The dial, calibrated in minutes, is normally set as soon as the canister has been activated.
When you have inflated the bag, set the timer for 45 minutes. When the pointer turns to zero, the bell will ring. You will then have 15 minutes to get out of the compartment. If there is an increase in resistance of breathing, or fogging of lenses on inhalation before the bell rings, immediately return to fresh air.
Get a new canister from the nearest repair locker and change canisters. Be sure not to handle the expended canister, as it will be very hot. Swing the bail out, and let the used canister drop out by itself.
That's about as much information as this article can give you. There is no substitute for practice.
Source: "What do You Know about OBA?" All Hands. 615 (April 1968): 28-31.