in the oxygen and exhale it just as if you were not
Airflow System
wearing an OBA. The moisture and carbon dioxide
At this point, you should know and understand the
from your exhaled breath activate the chemicals in the
use of each component of the OBA. Figure 5-11 shows
canister. The chemicals in the canister cleanse your
an OBA with a canister installed. The arrows indicate
exhaled breath of the moisture and carbon dioxide and
the airflow through the OBA.
return the cleansed air to you as you inhale.
1
9
2
8
7
3
4
5
6
DCf0511
1. Facepiece
5. Pressure relief valve
Figure 5-10. View A, front view of quick-starting canister for
2. Inhalation valve
6. Canister
use with Type A-4 oxygen breathing apparatus.
3. Inhalation tube
7. Exhalation tube
4. Breathing bag
8. Exhalation valve
QUICK STARTING CANISTER
9. Combination valve assembly
TOP
Figure 5-11. Airflow diagram.
RUBBER
COPPER
GASKET
As you exhale, moist breath passes through the
FOIL SEAL
OXYGEN
exhalation tube (7), through the valve housing to the
OXYGEN
bottom of the canister (6), and upward through the
CO2
chemical. The carbon dioxide is absorbed, and the
POTASSIUM
& H2O
SUPER
moisture present reacts with the chemical to give off
OXIDES
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
SODIUM
CHLORATE
drawn into the facepiece (1) by your normal intake of
breath.
CANDLE STARTER
DCf0510B
Check valves (2 and 8) are used in the inhalation
Figure 5-10. View B, cross-sectional view of quick-starting
canister.
and exhalation passages. An automatically operated
pressure-relief valve (5) in the breathing bag relieves
The amount of your exertion will determine how
excess pressure in the breathing bag. The speaking
long the canister produces oxygen. The more active
diaphragm, as described earlier, is built into the
you are, the faster the chemicals will be expended. The
facepiece.
canister will last longer when you are doing mild work,
such as investigating shipboard damage. When you are
OBA Operating Procedures
involved in hard work, such as fighting a fire, the
canister will last for about 30 minutes. Your normal
Damage Controlmen use the OBA on a regular
breathing habits will also effect the length of time the
basis for fire-fighting and training purposes. It will
canister will last. When you replace an expended
protect you; however, improper use of the OBA could
canister with a new canister, do so only in fresh air.
make you a personnel casualty. The following topics
5-7
