22-18 Change A
U.S. Navy Diving Manual—Volume 5
D = 165 fsw
2.
Substitute values and solve to find how long it will take for the
pressure to drop:
b. Increase the empty chamber pressure to 5 feet beyond the depth in
question. Open the exhaust valve and determine how long it takes to
come up 10 feet (for example, if checking for a depth of 165 fsw, take
chamber pressure to 170 feet and clock the time needed to reach 160
feet). Open the valve to different settings until you can determine what
setting will approximate the desired time. Record the setting. Calculate
the times for other rates and depths and determine the settings for these
times in the same way. Make a chart or table of valve setting versus
ventilation rate and prepare a ventilation bill, using this information
and the ventilation rules.
22-5.4.2
Notes on Chamber Ventilation.
The basic ventilation rules are not intended to limit ventilation. Generally, if
air is reasonably plentiful, more air than specified should be used for comfort.
This increase is desirable because it also further lowers the concentrations of
carbon dioxide and oxygen.
There is seldom any danger of having too little oxygen in the chamber. Even
with no ventilation and a high carbon dioxide level, the oxygen present would
be ample for long periods of time.
These rules assume that there is good circulation of air in the chamber during
ventilation. If circulation is poor, the rules may be inadequate. Locating the
inlet near one end of the chamber and the outlet near the other end improves
ventilation.
Coming up to the next stop reduces the standard cubic feet of gas in the cham-
ber and proportionally reduces the quantity (scfm) of air required for
ventilation.
Continuous ventilation is the most efficient method of ventilation in terms of
the amount of air required. However, it has the disadvantage of exposing the
divers in the chamber to continuous noise. At the very high ventilation rates
required for oxygen breathing, this noise can reach the level at which hearing
T
425
60
10
6
165
33
+
(
)
---------------------------------
=
215 seconds
=
T
215 seconds
60 seconds / minute
-------------------------------------------------
=
3.6 minutes
=
