Major DDS emergencies include loss of atmosphere control, loss of depth control
and fire in the DDC. Emergencies will be covered by locally prepared and
NAVSEA- or NAVFAC-approved emergency procedures. The following are
guidelines for establishing these procedures.
Loss of chamber atmosphere control
includes loss of oxygen control, high carbon dioxide level, chamber atmosphere
contamination and loss of temperature control.
Divers can be safely exposed to chamber oxygen partial
pressures between 0.16 and 1.25 ata; however, efforts should be implemented
immediately to correct the problem and reestablish normal oxygen levels. For an
oxygen partial pressure from 0.16 to 0.48 ata, the normal oxygen addition system
can be used to increase the oxygen level slowly over time. For an oxygen partial
pressure above 0.48, it may be necessary to secure the oxygen addition system and
allow the divers to breathe down the chamber oxygen to a normal level. Table 15-3
lists the chamber oxygen exposure time limits. If these limits are exceeded, the
divers should be placed on BIBS and the chamber ventilated to reduce the oxygen
level.
When the DDC’s life-support system loses its
ability to absorb carbon dioxide, the level of carbon dioxide within the chamber
will rise at a rate depending on the chamber size and the combined carbon dioxide
production rate of the divers. An increasing carbon dioxide level may be the result
of exhaustion of the carbon dioxide absorbent or inadequate gas flow through the
carbon dioxide absorbent canister. If, after the carbon dioxide absorbent canister is
changed, chamber carbon dioxide level still cannot be brought under 0.005 ata (3.8
mmhg), the flow through the canister may be inadequate. Divers shall don BIBS
when the chamber carbon dioxide level exceeds 0.06 ata (45.6 mmhg).
If an abnormal odor is detected or if several divers
report symptoms of eye or lung irritation, coughing, headache, or impaired performance,
contamination of the chamber atmosphere should be suspected. The divers
shall be placed on BIBS and emergency procedures executed. The divers should
be isolated in the part of the complex thought to be least contaminated. Test the
chamber atmosphere using chemical detector tubes or by collecting a gas sample
for analysis on the surface, as described in paragraph 15-19.2. If atmosphere
contamination is found, the divers should be moved to the chamber or PTC with
the least level of contamination and this chamber isolated from the rest of the
complex.(45.6 mmhg).
The allowable contaminant limits within a diving
system are based upon the Threshold Limit Values (TLV) for Chemical
Substances and Physical Agents guidelines published by the American Conference
of Governmental Industrial Hygienists (ACGIH). TLVs are the timeweighted
average concentration for an 8-hour work day and a 40-hour work week,
to which nearly all workers can be repeatedly exposed day after day without adverse effect. These guidelines are published yearly and should be used to determine
acceptability. Because the partial pressure of a gas generally causes its
physiological effects, the published limits must be corrected for the expected
maximum operating depth (ata) of the diving system.
The solution to an atmosphere contamination problem centers around identifying
the source of contamination and correcting it. Gas samples from suspected sources
must be checked for contaminants. Special attention should be given to recently
changed and cleaned piping sections, gas hoses, and diver umbilicals, any of
which may contain residual cleaning solvents. Surfaced chambers should be thoroughly
ventilated with air or a breathable helium-oxygen mixture (to prevent
hypoxia in maintenance personnel), inspected, and thoroughly scrubbed down to
remove residual contaminants. These chambers can then be compressed to depth
using a gas bank that is free of contaminants, the divers can be transferred to this
chamber, and the surface cleaning process can be repeated on the remaining
chamber(s). After cleaning and compression to depth, the chamber should be
checked periodically for recurrence of the contamination.
Loss of temperature control of more than 2–3°F
above or below the comfort level may lead to severe thermal stress in the divers.
Studies have shown that heat loss by perspiring is less effective in a hyperbaric
atmosphere. Heating a chamber to warm up cold divers may result in the divers
rapidly becoming overheated. Heat stroke may then become a possibility. The
potential for uncontrolled chamber heating occurs when chambers and PTCs are
exposed to direct sunlight
When the chamber temperature falls, the divers begin intense shivering and hypothermia
develops unless rapid and aggressive measures are taken to correct the
problem. Divers may be provided with insulated clothing, blankets, and sleeping
bags. The best of these insulators are of limited effectiveness within the heliumoxygen
environment and will provide marginal protection until the problem can be
corrected. Special thermal protection systems have been designed for the use
within DDCs. These systems include thermal protection garments, insulating deck
pads or hammocks, and combination carbon dioxide absorbent and respiratoryheat
regenerator systems.
Loss of depth control is defined as a pressure loss or gain
that cannot be controlled within the normal capabilities of the system. When loss
of depth control is encountered, all deployed divers shall be recovered immediately
and all divers placed on BIBS. Attempt to control depth by exhausting excess
gas or adding helium to minimize depth loss until the cause can be found and
corrected. If the depth change is in excess of that allowed by the Unlimited Duration
Excursion Tables, the divers should be returned to the original storage depth
immediately and the Diving Medical Officer notified.
Because fire within a DDC may progress rapidly, the divers and
watchstanders must immediately activate the fire suppression system and secure
the oxygen system as soon as a fire is suspected. When the fire suppression system is activated, all divers shall immediately go on BIBS. Watchstanders should
monitor depth carefully because an extensive fire will cause an increase in depth.
If the fire suppression system fails to extinguish the fire, rapid compression of the
chamber with helium may extinguish the fire, in that helium lowers the oxygen
concentration and promotes heat transfer. After the fire is extinguished, chamber
atmosphere contaminant emergency procedures shall be followed.
PTC emergencies, like DDC emergencies, require specific,
timely, and uniform responses in order to prevent injury or casualty to divers,
watchstanders, and equipment.
