Predive Checklist. To ensure each item is operational and ready for use, perform
the equipment checks listed in the Recompression Chamber Predive Checklist,
Figure 22-11a.
Safety Precautions.
-
Do not use oil on any oxygen fitting, air fitting,
or piece of equipment.
-
Do not allow oxygen supply tanks to be depleted
below 100 psig.
-
Ensure dogs are in good operating condition and
seals are tight.
-
Do not leave doors dogged (if applicable) after
pressurization.
-
Do not allow open flames, smoking materials, or any
flammables to be carried into the chamber.
-
Do not permit electrical appliances to be used in
the chamber unless listed in the Authorized for Navy Use (ANU).
-
Do not perform unauthorized repairs or
modifications on the chamber support systems.
-
Do not permit products in the chamber that may
contaminate or off-gas into the chamber atmosphere.
General Operating Procedures.
1. Ensure completion of Predive Checklist.
2. Diver and tender enter the chamber together.
3. Diver sits in an uncramped position.
4. Tender closes and dogs (if so equipped) the inner lock door.
5. Pressurize the chamber, at the rate and to the depth specified in
the appropriate decompression or recompression table.
6. As soon as a seal is obtained or upon reaching depth, tender
releases the dogs (if so equipped).
7. Ventilate chamber according to specified rates and energize CO2
scrubber and chamber conditioning system.
8. Ensure proper decompression of all personnel.
9. Ensure completion of Postdive Checklist.
Tender Change-Out. During extensive treatments, medical personnel may prefer
to lock-in to examine the patient and then lock-out, rather than remain inside
throughout the treatment. Inside tenders may tire and need relief.
Lock-In Operations. Personnel entering the chamber go into the outer lock and
close and dog the door (if applicable). The outer lock should be pressurized at a
rate controlled by their ability to equalize, but not to exceed 75 feet per minute.
The outside tender shall record the time pressurization begins to determine the
decompression schedule for the occupants when they are ready to leave the
chamber. When the pressure levels in the outer and inner locks are equal, the
inside door (which was undogged at the beginning of the treatment) should open.
Lock-Out Operations. To exit the chamber, the personnel again enter the outer
lock and the inside tender closes and dogs the inner door (if so equipped). When
ready to ascend, the Diving Supervisor is notified and the required decompression
schedule is selected and executed. Constant communications are maintained with
the inside tender to ensure that a seal has been made on the inner door. Outer lock
depth is controlled throughout decompression by the outside tender.
Gag Valves. The actuating lever of the chamber gag valves shall be maintained in
the open position at all times, during both normal chamber operations and when
the chamber is secured. The gag valves must be closed only in the event of relief
valve failure during chamber operation. Valves are to be lock-wired in the open
position with light wire that can be easily broken when required. A WARNING
plate, bearing the inscription shown below, shall be affixed to the chamber in the
vicinity of each gag valve and shall be readily viewable by operating personnel.
The WARNING plates shall measure approximately 4 inches by
6 inches and read as follows:
WARNING
The gag valve must remain open at all times.
Close only if relief valve fails.
Ventilation. The basic rules for ventilation are presented
below. These rules permit rapid computation of the cubic feet of air per
minute (acfm) required under different conditions as measured at chamber
pressure (the rules are designed to ensure that the effective concentration
of carbon dioxide will not exceed 1.5 percent (11.4 mmHg) and that when
oxygen is being used, the percentage of oxygen in the chamber will not
exceed 25 percent).
1. When air is breathed, provide 2 cubic feet per
minute (acfm) for each diver at rest and 4 cubic feet per minute (acfm) for
each diver who is not at
rest (i.e., atender actively taking care of a
patient).
2. When oxygen is breathed from the built-in breathing system (BIBS),
provide 12.5 acfm for a diver at rest and 25 acfm for a diver who is not at
rest.
When these ventilation rates are used, no additional ventilation is
required for personnel breathing air. These ventilation rates apply only to
the
number of people breathing oxygen and are used only when no BIBS dump
system is installed.
3. If ventilation must be interrupted for any reason, the time should
not exceed 5 minutes in any 30-minute period. When ventilation is resumed,
twice
the volume of ventilation should be used for the time of interruption
and then the basic ventilation rate should be used again.
4. If a BIBS dump system is used for oxygen breathing, the
ventilation rate for air breathing may be used.
5. If portable or installed oxygen and carbon dioxide monitoring
systems are available, ventilation may be adjusted to maintain the oxygen
level below
25 percent by volume and the carbon dioxide level below 1.5
percent surface equivalent (sev).
Chamber Ventilation Bill. Knowing how much air must be used does not solve the
ventilation problem unless there is some way to determine the volume of air actually
being used for ventilation. The standard procedure is to open the exhaust
valve a given number of turns (or fraction of a turn), which will provide a certain
number of cubic feet of ventilation per minute at a specific chamber depth, and to
use the supply valve to maintain a constant chamber depth during the ventilation
period. Determination of valve settings required for different amounts of ventilation
at different depths is accomplished as follows.Treatment During Surface-Supplied HEO2 and MK 16 Operations.
Treatment of
decompression sickness arising in the water in specific operational environments
is presented in Volume 3 for surface-supplied helium-oxygen dives and Volume 4
for MK 16 diving operations.
WARNING This procedure is to be
performed with an unmanned chamber to avoid exposing occupants to
unnecessary risks.
-
Mark the valve handle position so that it is possible
to determine accurately the number of turns and fractions of turns.
-
Check the basic ventilation rules above against
probable situations to determine the rates of ventilation at various
depths (chamber pressure) that
may be needed. If the air supply is ample, determination of ventilation
rates for a few depths (30, 60, 100, and 165 feet) may be sufficient. It
will beconvenient to know the valve settings for rates such as 6, 12.5,
25, or 37.5 cubic feet per minute (acfm).
-
Determine the necessary valve settings for the
selected flows and depths by using a stopwatch and the chamber as a
measuring vessel.
a. Calculate how long it will take to
change the chamber pressure by 10 feet if the exhaust valve lets air
escape at the desired rate close
to the depth in question. Use the
following formula.
Example: Determine how long it will take the pressure to drop from 170
to 160 feet in a 425-cubic-foot chamber if the exhaust valve is releasing 6
cubic feet of air per minute (measured at chamber pressure of 165 feet).
1. List values from example:
T = unknown
V = 425 cf
R = 6 acfm
P = 10 fsw
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.
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 chamber 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 loss becomes a hazard to
the divers in the chamber. If high sound levels do occur, especially
during exceptionally high ventilation rates, the chamber occupants must
wear aural protectors (available as a stock item). A small hole should
be drilled into the central cavity of the protector so that they do not
produce a seal which can cause ear squeeze.
- The size of the chamber does not influence the rate (acfm) of air required for
ventilation.
