MSA OBA A-4

 

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PROTECTIVE EQUIPMENT MSA (OBA) A-4

 

The Navy uses a wide variety of special fire fighter's protective equipment. It includes the oxygen breathing apparatus, protective masks, proximity suits, tending lines, and atmospheric testing equipment plus gloves, helmet, anti-flash hood and voice amplifier. You will need to know what equipment is available, how to operate it, and how to maintain it in top operating condition.

OXYGEN BREATHING APPARATUS

The type A-4 oxygen breathing apparatus (OBA) is used throughout the Navy. The OBA is an entirely self-contained breathing apparatus. It enables the wearer to breathe independently of the outside atmosphere. It produces its own oxygen and allows the wearer to enter compartments, voids or tanks that contain smoke, dust, or fire, or those that have a low oxygen content.

Major OBA Components

You will be required to wear, operate, and maintain in perfect operating condition the type A-4 OBA. To do so, you must know the various components of the OBA and their purposes. Figure 6-1 shows the components and identifies them. As you read about the various components, refer to this figure as well as to those pertaining to the individual components.

FACEPIECE.-
The facepiece (fig. 6-2) contains the eyepiece, the speaking diaphragm, and the head straps. The eyepiece is a one-piece clear lens. A spectacle kit is provided that may be installed in the facepiece. Corrective lenses may be installed in the kit for individuals who require glasses. However, once the lenses are installed, only the person that the lenses are made for can

Figure 6-1.-Components of the OBA.

Figure 6-3.-Breathing tubes.

tubes to control the oxygen. The breathing bag contains the oxygen that is generated by the canister for you to breathe. One breathing tube transports the oxygen from the breathing bag to the facepiece (fig. 6-3); the other transports the exhaled air back to the canister. Both tubes are made of corrugated rubber. They control the flow of air and help cool the air for your comfort when you wear the OBA. The tubes are a quick-disconnect type. The tube couplings are color coded, and the supply tube is of a different size than the exhaust tube. This prevents the possibility of connecting the tubes to the wrong couplings.

TIMER.-
The timer (figs. 6-1 and 6-4) is located so that you can check the amount of

Figure 6-2.-Facepiece with spectacle kit installed.

use that spectacle kit. The speaking diaphragm allows you to talk to others and to use communication devices such as sound-powered telephones. The head straps hold the facepiece snug against your face. If the straps are adjusted properly, no outside gases can get inside of the facepiece.


BREATHING BAG AND TUBES.-
The OBA has a breathing bag and two breathing

Figure 6-4.-Timer.

time remaining as you go about your duties. The timer's bells are made to ring for 8-10 seconds continuously.

 

BREASTPLATEASSEMBLY.-

The breast-plate assembly (fig. 6-5) houses the plunger assembly, canister guard and holder, and the handle. The plunger pierces the copper foil seal of the canister when the canister is seated in place. The handle actuates the seating mechanism that positions the canister in its housing. When activated, the canister's chlorate candle provides you with oxygen to breathe. The canister gets very hot, but the canister guard or holder protects you from the heat produced by the canister.

COMBINATION VALVE ASSEMBLY.-

The combination valve assembly is shown in figure 6-6. It directs the flow of air through the canister to the breathing bag.

HARNESS AND WAIST STRAPS.-

 The OBA has two types of straps: harness and waist (fig. 67). The harness straps go over your shoulders and snap into D rings. They support the weight of the OBA. The waist strap goes around your body and helps keep the OBA from swinging away from you.

 

 

 

 

OBA QUICK-STARTING CANISTER.- The quick-starting canister (fig. 6-8) is painted

Figure 6-5.-Breastplate assembly.

Figure 6-6.-Combination valve assembly.

green. This is the canister that you will use for all evolutions other than training. The training canister is discussed later. Figure 6-9 shows a cutaway view of the canister. The rubber gasket provides an airtight seal when the canister is in the operating position in the OBA. The copper foil seal protects the chemicals from moisture until the canister is ready for use. The chlorate candle, which is built into the canister, produces oxygen for about 5 minutes. You will be able to breathe in the oxygen and exhale it just as if you were not wearing an OBA. The moisture and carbon dioxide from your exhaled breath activate the chemicals in the canister. The chemicals in the canister cleanse your exhaled breath of the moisture and carbon dioxide

Figure 6-7.-Harness and waist strap.

Figure 6-8.-Front view of quick-starting canister for use with Type A-4 oxygen breathing apparatus.

Figure 6-9.-Cross-sectional view of quickstarting canister.

and return the remainer of the air to you as you inhale.

The amount of your exertion will deter-mine how long the canister produces oxygen. The more active you are, the faster the chemicals will be expended. The canister will last longer when you are doing mild work such as investigating shipboard damage. When you are involved in hard work, such as fighting a fire, the canister will last for about 30 minutes. Your normal breathing habits will also effect the length of time the canister will last. When you replace an expended canister with a new canister, do so only in fresh air.

Airflow System

At this point, you should know and understand the use of each component of the

OBA. Figure 6-10 shows an OBA with a canister installed. The arrows indicate the airflow through the OBA.

As you exhale, moist breath passes through the exhalation tube (7), through the valve housing to the bottom of the canister (6), and upward through the chemical. The carbon dioxide is absorbed, and the moisture present reacts with the chemical to give off oxygen. This oxygen passes into a breathing bag (4) (part of the breastplate group) from which the inhalation tube (3) allows the breathable mixture to be drawn into the facepiece (1) by your normal intake of breath.

Check valves (2 and 8) are used in the inhalation and exhalation passages. An automatically operated pressure-relief valve (5) in the breathing bag relieves excess pressure in the breathing bag. The speaking diaphragm, as described earlier, is built into the facepiece.

Figure 6-10.-Airflow system.

OBA Operating Procedures

Damage Controlmen use the OBA on a regular basis for fire-fighting and training purposes. It will protect you; however, improper use of the OBA could make you a personnel casualty. The following topics discuss the type A-4 OBA operating procedures. It is very important that you learn to use them properly. You should practice the operating procedures under the supervision of a leading petty officer who is qualified in the use of the OBA. Do not use the green quick-starting canister for training; check with the DCA about using a red training canister.

DONNING THE OBA.- When donning the OBA, do so in the following order:

1. With one hand, grasp the facepiece at the combination valve housing and the apparatus at the operating handle. With the other hand, grasp the straps of the body harness and the body pad D ring. Bring the pad and harness over your head while positioning the OBA on your chest. See figure 6-11.

2. Find the two straps hanging free in back (view A, fig. 6-12). Attach the end of

Figure 6-11.-Step 1 of donning the OBA.

Figure 6-12.-Step 2 of donning the OBA.

each strap to the ring on each side of the breastplate (view B, fig. 6-12).

3. Position the breastplate on your chest so that the breathing tube connections are slightly below your shoulders. Your head movement should not be restricted when you don the facepiece. While holding the apparatus in this position, adjust the two underarm straps and then adjust the two shoulder straps (fig. 13)

Figure 6-13.-Step 3 of donning the OBA.

until the apparatus fits comfortably. The harness pad should be located in the center of your back down from the neck for a comfortable fit.

4. Place the facepiece over your head in the standby position (fig. 6-14) until you are ready to activate the canister.

5. Snap the waist strap to the bracket on the lower side corner of the breastplate

Figure 6-14.-Step 4 of donning the OBA. 6-7

Figure 6-15.-Step 5 of donning the OBA.

(fig. 6-15) and adjust to hold the apparatus snugly to your body. To secure the excess loop of the waist strap, wrap it under the secured part of the strap. Secure the ends of the lower body harness straps under the waist strap if they extend down to your waist after being adjusted.

6. Install the canister in the following manner:

a. Remove the tear-off cap of the canister by pulling the tab backward and downward to expose the copper-foil seal (fig. 6-16). Discard the cap.

b. Remove the canister candle cover by rotating the swivel plate 1800. Push it down toward the center of the canister, as shown in view A of figure 6-17. Leave the cover dangling by the lanyard, as shown in view B of figure 617. When you remove the candle cover, do NOT

pull the lanyard so that the cotter pin is removed. The removal of the cotter pin fires the candle, and the canister starts generating oxygen. If this happens while the copper-foil seal is intact, internal pressure in the canister will build up. This pressure will cause the copper foil seal or the canister seam to rupture.

c. Hold the canister with the neck up and the concave, or ribbed side, toward your body. Insert the canister upward into the guard and breastplate assembly (fig. 6-18) until the canister is firmly in place. The canister is now locked in a standby position with the copper-foil seal still intact. If the copper-foil seal is pierced when the canister is placed in the standby position, the standby stop will need to be adjusted. An OBA that pierces the copper-foil seal in the standby position is NOT to be used until the adjustments are made.

7. Don and adjust the facepiece as follows:

a. Place the head harness straps over the front of the facepiece.

b. Insert your chin into the chin stop of the facepiece (view A of fig. 6-19).

c. Pull the head straps from the front of the facepiece over your head (view B of fig. 619). Be sure your hair is not under the facepiece shield.

d. Make sure the straps lie flat against your head.

e. Tighten the lower straps (neck straps) first.

f. Tighten the side straps.

g. Place both hands on the head harness pad (on the back of your head) and push it down toward your neck.

h. Repeat steps e and f.

Figure 6-16.-Step 6 removing tear-off cap.

Figure 6-17.-Removing the candle cover, views A and B.

i. Tighten the forehead or front strap, if needed.

8. Test the facepiece for a good seal by squeezing the corrugated breathing tubes tightly to prevent the passage of air (fig.

Figure 6-18.-Inserting the canister.

Figure 6-19.-Donning the facepiece, views A and B.

6-20). Inhale gently so the facepiece collapses slightly, and hold your breath for 10 seconds. The facepiece will remain collapsed while your breath is held if the assembly is gas tight. If you detect any leakage around the face seal, readjust your head harness straps. If you detect other than face-seal leakage, investigate the condition and correct it. You MUST test the facepiece for a seal before each use.

9. Make final adjustments on all four body harness straps. You should be able to look up or down without having the facepiece shift or catch on the timer or the main valve housing.

10. If you are going into a standby or ready condition, loosen only the lower facepiece straps and then remove the facepiece. Place the facepiece over your head and out of the way until ready to start the canister and put the OBA into operation. In an emergency, eliminate this step.

STARTING THE CANISTER.- When you are ready to enter the contaminated area, start the canister in the following manner:

1. If your facepiece is in the standby position, put it on before starting the canister. Retighten the lower straps and retest your facepiece for a proper seal.

2. Unlock the bail assembly handle of the OBA by using both hands to depress the tabs from the bottom lock. Swing the handle upward until it snaps. Test the handle to see if it is locked by

Figure 6-20.-Airtightness of the facepiece.

lightly pushing the handle forward without depressing the tabs.

3. Pull the lanyard on the canister straight out and away from your body. This removes the cotter pin (fig. 6-2 1), fires the candle, and inflates the breathing bag with oxygen. After you pull the lanyard, always check to ensure that the cotter pin is still attached to the lanyard. A slight amount of harmless smoke maybe present in the facepiece while the candle is burning.

4. Now, test the tube connectors, canister, and breathing bags for tightness. While the candle is filling the breathing bag, depress the breathing bag at the pull tab with your left hand. Regrasp and seal off both breathing tubes with your right hand, while pressing against the right side of the breathing bag with your right elbow (fig. 6-22). The bag must be compressed at the pull tab so that the relief valve does not vent during this test. The bag must remain inflated; otherwise, there may be a leak in the OBA, which you must correct before you use the OBA.

5. Breathe normally. The chemical reaction of the canister will generate more oxygen than you require. If too much oxygen is produced, the extra oxygen will be vented automatically by the relief valve in the bag when the bag reaches full capacity. A manual relief pull tab on the valve (fig. 6-23) is provided in case the valve sticks in the closed position during a long period of storage. DO NOT pull the breathing bag tab

Figure 6-21 .-Checking for the cotter pin.

Figure 6-22.-Testing the OBA.

during normal use. If you do, you will vent your breathing oxygen from the breathing bag to the atmosphere.

In the event of a malfunction of the candle, you can activate the canister manually. The manual starting of the canister is not recommended. The procedures listed here are to be used only when the chlorate candle has misfired and sufficient time is available to start the canister manually, or if there is a shortage of available canisters. Under no circumstances should you save

Figure 6-23.-Manual relief valve tab.

the chlorate candle to use for an emergency exit of the space. Such practice is dangerous, and the candles have been known to misfire.

You must be in a clean atmosphere when manually starting the canister. Use the following procedures:

1. Work one finger under the edge of your facepiece, stretching the mask slightly to break the seal.

2. Inhale while grasping and squeezing both breathing tubes with your other hand. This will allow you to draw external air from outside the facepiece.

3.Release the breathing tubes, remove your finger to reseal the mask, and exhale into the facepiece.

4.Continue this cycle until your breathing bag is fully inflated. Exhaust the air in the breathing bag by exerting pressure on the right-hand side until the bag on the right is deflated. In this process, your moist breath passes through the canister to start the chemical reaction. One filling of the bag is not usually sufficient to fully activate the canister

5. Repeat steps 1 through 4 to reinflate and deflate the breathing bag at least five times. Now, without gloves, cautiously feel the bottom of the canister. If the entire bottom of the canister is warm, oxygen is being generated. The apparatus is then ready for setting the timer and for the operational check. If the canister is not warm, repeat steps 1 through 4. In cooler temperatures, several cycles of inflation and deflation of the bag may be required to start oxygen production.

SETTING THE TIMER.- To set the timer, grasp the knob on the timer. Turn the knob clockwise to 60 minutes, and then turn it counterclockwise to 30 minutes. By setting the timer to 60 first, you fully wind the alarm bell spring. When 30 minutes have expired, the warning bell will sound continuously for 10 or more seconds. When you have set the timer, you are ready to enter a hazardous atmosphere.

REMOVING AN UNUSED CANISTER.- If the canister's copper-foil seal has not been punctured, remove the canister by placing one hand on the bottom of the canister and pulling the canister releasing strap. You do not need to wear gloves in this situation. The handle must also be in the load and standby positions.

Once the canister is removed, protect the copper-foil seal by installing one of the spare aluminum caps that are provided for this purpose.

REMOVING A USED CANISTER.- When you remove a hot canister, you need to protect your hands with approved protective gloves.

Once the canister has been used, remove the facepiece and put it over your head in the standby position. Then, unlock the handle from the operation position and swing it down to the load and standby positions.

Next, unfasten the waist strap, spread your feet apart and lean the upper part of your body slightly forward. To release the used canister, pull the canister release strap (fig. 6-24). The canister will drop out of the apparatus (fig, 6-25). Drop the canister ONLY on a clean, dry deck.

You need to be careful when you remove used canisters from the OBA. They are hot, and the chemicals inside of the canister can cause serious chemical burns if they get on your skin. The chemicals are similar to caustic soda, also known as lye. Normally, you will not have chemicals spilling out of the canister, but there is always the possibility. Finally, the chemicals will cause a violent explosion if they come into contact with a petroleum-base substance.

DISPOSAL OF USED CANISTERS.- You must dispose of an OBA quick-starting canister as soon as possible after it has been used or when the copper-foil seal has been punctured.

If your ship is more than 25 nautical miles from shore, you may throw the canister overboard. To dispose of the canister in this manner, first obtain permission from the officer of the deck. Once permission has been granted, ensure that the canister cap is removed and the copperfoil seal is fully punctured. This will allow water to enter the canister. DO NOT puncture holes

Figure 6-24.-Releasing the canister.

Figure 6-25.-Dropping the canister.

in the bottom or sides of the canister. Make sure there is no oil in the water. Then throw the canister overboard. If oil gets inside of the canister, a violent explosion will occur.

If you are within 25 nautical miles of shore, do not throw the canister overboard. Instead, let it cool down for at least 30 minutes. (If a canister was not used, but the copper-foil seal has been punctured, place the canister in a clean bucket. Light off the canister and let it set for 15 minutes to cool.) When the canister is cool enough to handle, place a new metal cap, NSN 4240-00-089-7963, on the neck to cover the punctured copper-foil seal. Then double wrap the canister in a poly bag, NSN 8105-00-2998532, or its equivalent. The wrapped canister should then be stored in a dry, oil-free area until it can be disposed of at sea or turned over to a shore facility for disposal.

When the ship is in port, contact the department ashore that is responsible for hazardous waste. Make arrangements with that department to turn all canisters over to them for disposal.

REMOVING THE OBA.- Remove the OBA in the following manner:

1. Remove the facepiece by releasing the head straps at the buckles with your fingertips before pulling the headpiece off. If the canister is still in the OBA, place the facepiece over your head

in the standby position and remove the canister. NEVER remove the OBA with a canister in place.

2. If the facepiece is in standby position, you should remove it and let it hang in front of the OBA.

3. Loosen the waist strap, then unhook it.

4. Loosen the shoulder straps and unhook the harness at the upper corners of the breastplate assembly. Grasp the facepiece and operating handle with one hand and the shoulder harness (preferably at the D-ring connector) with your other hand. Lift the OBA over your head.

5. If the OBA is wet or moist, wipe it down.

6. Always clean the outside body of the OBA after each use with a mild solution of soap and warm water.

7. Disinfect the inside of the facepiece. Mix the disinfectant (NSN 95-6840-00-526-1129) as stated on the container label. Use a sponge that is moist, but not dripping, with the disinfectant solution.

OBA Equipment Stowage

Before stowing the OBA, the facepiece should be protected to prevent scratches and abrasions. All OBA equipment and canisters must be stored in a cool, dry place. The life of an OBA will be

Figure 6-26.-OBA storage locker.

lengthened if it is stored under these conditions. The term cool denotes temperatures ranging from above freezing to 110F (43C) when storage is out of direct sunlight. The term dry usually denotes a storage area where condensation does not come in contact with the equipment.

The only places the OBA should be stowed onboard ship are in repair lockers or in OBA lockers (fig. 6-26). These lockers have provisions for stowing the OBA in a flat position. You should ensure that the facepiece is properly protected to prevent scratching or scarring of the lens. The canisters should be stowed with the concave side down. Additional information on cleaning, inspecting, and testing of the type A-4 OBA can be found in the Naval Ships' Technical Manual, chapter 079, volume 2.

TENDING LINES

Tending lines are used as a precautionary measure to help rescue an investigator or fire fighter who is wearing an oxygen breathing apparatus, air-line mask, or similar equipment.

A 50-foot nylon covered, steel wire tending line (fig. 6-27) is used aboard ship with the oxygen breathing apparatus or the air-line mask. The tending line has a stout hook on each end that is closed with a snap catch. The line is pliable and can slide freely around obstructions.

If necessary, the rescue should be accomplished by having another person equipped with a breathing apparatus follow the tending line to the person to be rescued. Do not attempt to drag the person out by the tending line. The line may become fouled on some obstruction or part the wearer's harness. This will mean a loss of time,

Figure 6-27.-Tending line.

CAUTION A stricken person must never be hauled by a line attached to the waist. A person may be dragged by the waist a short distance along the deck, but his/her weight must never be suspended from the waist. If the wearer lacks any sort of shoulder harness, the line must be made fast so that it passes around the upper part of the body and under the arms, and meets either in front or the back. The tender should wear rubber gloves and shoes when handling steel tending lines or cables.

and it will still be necessary to send another person in. If the rescue is to be effected promptly, someone must be equipped with an OBA that is ready for immediate use and must be standing by ready for immediate entry. Tending lines may also be used by fire fighters to find their way back to fresh air to change canisters when the visibility is poor because of heavy smoke.

When the OBA is used to inspect damage or to fight fires, a team of one wearer and one person to handle the tending line should work together. If two or more OBAs are used in the same compartment, the tending lines are not used. However, the personnel wearing the OBAs should keep in constant sight or touch with each other.

The OBA wearer and the line tender should both know and use the following system of line signals

Code

Pull

Meaning

O

1

OK

A

2

Advance

T

3

Take up

H

4

Help

OBA TRAINING CANISTER KIT

The OBA training canister kit-FSN 2H-424000-238-9959--(fig. 6-28) is designed to provide realistic training in the classroom for 40 trainees. These trainees don the OBA and properly activate the quick-start OBA (training) canister. The training canister is red in color and is functionally identical to the regular green quick-start canister.

Figure 6-28.-Training canister assembly-exploded view.

However, there is one important distinction: The training canister contains a chemical filler (baralyme), which only absorbs the carbon dioxide (CO2) from exhaled breath. It does not produce oxygen. There is enough baralyme to absorb the CO2 that will be exhaled by the 40 trainees who use the canister for 5 minutes each AT REST.

NOTE: The canister should be discarded after it is used by 40 trainees, or when the chemical in the view window of the canister body changes color from pink to solid blue, whichever occurs first.

The oxygen candle assembly produces about 10 liters of oxygen. In the training canister, this is enough to provide 5 minutes of oxygen for one person AT REST. The danger of a training canister being used during an actual casualty is obvious. To prevent inadvertent use and possible serious injury or a fatality, the training canisters should NEVER be stowed in OBA lockers or in the vicinity of damage control equipment.

For the initial charging of a training canister, use the following procedures:

1. Remove the cover from the firing mechanism. Remove the firing mechanism and storage plug. Save the plug to reuse when storing a partially used canister to prevent moisture from entering the canister body.

2. Insert a candle assembly into the candle recess of the canister. Make sure the gasket is flat against the bottom of the canister.

3. Place the firing mechanism over the candle assembly with the primer housing projecting through the center hole and with the notches lined up with the tangs. The notches and tangs are positioned so that the unit can only be assembled in the correct position.

4. Rotate the firing mechanism clockwise to lock the candle in place. Tighten the firing mechanism until the frame contacts the tangs. Do not overtighten.

5. Fold the lanyard into the candle cover and secure the assembly on the firing mechanism frame. The training canister is now ready for use with the OBA.

To recharge a canister that has just been used, use the following procedures:

1. Position and secure a new metal tear-off cap on the canister neck so that the tab points toward the instruction label on the convex side of the canister.

2. Remove the firing mechanism from the bottom of the canister by turning it counterclockwise until the tangs line up with the notches.

3. Remove the used candle and place it in a regular trash can after it has cooled.

4. Hold the firing mechanism (fig. 6-29) with the slotted end of the frame pointing toward you. Raise the firing hammer to the cocked position.

5. While holding the firing hammer in the

cocked position, insert the cotter pin through the holes in the frame from the same side as the rivet head. Secure the cotter pin by bending the long leg slightly.

The remainder of the recharging procedure is the same as steps 2, 3, 4, and 5 of the initial charging procedure.

To start a training canister after it has been charged, use the following procedures:

1. Remove the tear-off cap from the top of the CHARGED canister by pulling it straight backward and downward; remove the disk to expose the gasket.

2. Remove the candle cover by rotating the swivel plate 180; push the swivel plate and cover down toward the center of the canister. Let the cover dangle on the lanyard. DO NOT PULL THE LANYARD.

Figure 6-29.-Detailed assembly of firing mechanism.

3. Insert the training canister into the OBA to the standby position.

4. Move the training canister into the operating position by lifting the handle upward, ensuring that the canister is snug in the canister guard.

5. Don and adjust the facepiece, and check it for an airtight fit.

6. Pull the lanyard straight out away from your body. This removes the cotter pin and fires the candle, which inflates the bag with oxygen within 15 seconds.

7. Set the timer on the OBA by turning it clockwise to 60; then, return it to 5.

To remove the canister, you should follow the same procedures used for removing an unused canister (discussed earlier in this chapter). However, you must wear protective gloves because the canister will be hot. If the canister is to be reused by another person, charge it as previously discussed.

Training Kit Stowage

Training canister kits are to be stowed in a special locker provided or in a locked compartment. This kit is to be kept locked at all times, except when it is in actual use. The keys should be controlled by the damage control officer

to ensure that the training canisters are used only for training.

After training sessions or for breaks in training of 1 hour or more, a partially used canister should be sealed. To seal the canister, place a metal tear-off cap on the canister neck, remove the oxygen candle, and lock the plastic storage plug in the candle recess in the canister bottom by the firing mechanism. The canister should be returned to the special locker or compartment and locked. Where lockers are not provided, stow the canister in a cool, dry storeroom.

Training Kit Disposal

After the chlorate oxygen candles have been burned, they contain sodium chloride (table salt) and partially oxidized iron. They may be discarded in a regular trash container after they have cooled.

Expended training canisters do not have the hazards of the regular quick-start canister. However, for the training benefit, they should be disposed of in the same manner as the regular quick-start canister.

 

 

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