preparing for a mixed-gas
decompression dive. Note the
backplate and wing setup with
side mounted stage tanks containing
EAN50 (left side) and pure
oxygen (right side). Both equipment and procedures can be adapted to deal with the problems of greater depth. Usually the two are combined, as the procedures must be adapted to suit the equipment, and in some cases the equipment is needed to facilitate the procedures.
Equipment adaptations for deeper diving The equipment used for deep diving depends on both the depth and the type of diving.
Scuba is limited to equipment that can be carried by the diver or is easily deployed by the
dive team, while
surface-supplied diving equipment can be more extensive, and much of it stays above the water where it is operated by the
diving support team. • Scuba divers carry larger volumes of
breathing gas to compensate for the increased gas consumption and decompression stops. •
Rebreathers, though more complex, manage gas much more efficiently than
open-circuit scuba. • Use of
helium-based breathing gases such as
trimix reduces
nitrogen narcosis and reduces the
toxic effects of oxygen at depth. • A
diving shot, a
decompression trapeze, or a
decompression buoy can help divers control their ascent and return to the surface at a position that can be monitored by their surface support team at the end of a dive. • Decompression can be
accelerated by using specially blended breathing gas mixtures containing lower proportions of inert gas. •
Surface supply of breathing gases reduces the risk of running out of gas. • In-water decompression can be minimized by using
dry bells and
decompression chambers. •
Hot-water suits can prevent
hypothermia due to the high heat loss when using helium-based breathing gases. •
Diving bells and
submersibles expose the diver to the direct underwater environment for less time, and provide a relatively safe shelter that does not require decompression, with a dry environment where the diver can rest, take refreshment, and if necessary, receive first aid in an emergency. • Breathing gas s reduce the cost of using helium-based breathing gases, by recovering and recycling exhaled surface supplied gas, analogous to rebreathers for scuba diving. • The most radical equipment adaptation for deep diving is to isolate the diver from the direct pressure of the environment, using armoured
atmospheric diving suits that allow diving to depths beyond those currently possible at ambient pressure. These rigid, articulated exoskeleton suits are sealed against water and withstand external pressure while providing life support to the diver for several hours at an internal pressure of approximately normal surface
atmospheric pressure. This avoids the problems of
inert gas narcosis,
decompression sickness,
barotrauma,
oxygen toxicity, high
work of breathing,
compression arthralgia,
high-pressure nervous syndrome and
hypothermia, but at the cost of reduced mobility and dexterity, logistical problems due to the bulk and mass of the suits, and high equipment costs.
Procedural adaptations for deeper diving Procedural adaptations for deep diving can be classified as those procedures for operating specialized equipment, and those that apply directly to the problems caused by exposure to high ambient pressures. • The most important procedure for dealing with physiological problems of breathing at high ambient pressures associated with deep diving is
decompression. This is necessary to prevent inert gas bubble formation in the body tissues of the diver, which can cause severe injury.
Decompression procedures have been derived for a large range of pressure exposures, using a large range of gas mixtures. These basically entail a slow and controlled reduction in pressure during ascent by using a restricted ascent rate and
decompression stops, so that the inert gases dissolved in the tissues of the diver can be eliminated harmlessly during normal respiration. •
Gas management procedures are necessary to ensure that the diver has access to suitable and sufficient breathing gas at all times during the dive, both for the planned dive profile and for any reasonably foreseeable contingency. Scuba gas management is logistically more complex than surface supply, as the diver must either carry all the gas, must follow a route where previously arranged gas supply depots have been set up (stage cylinders). or must rely on a team of support divers who will provide additional gas at pre-arranged signals or points on the planned dive. On very deep scuba dives or on occasions where long decompression times are planned, it is a common practice for support divers to meet the primary team at decompression stops to check if they need assistance, and these support divers will often carry extra gas supplies in case of need. (
AP Diving "Inspiration"). •
Rebreather diving can reduce the bulk of the gas supplies for long and deep scuba dives, at the cost of more complex equipment with more potential failure modes, requiring more demanding procedures and higher procedural task loading. •
Surface supplied diving distributes the task loading between the divers and the support team, who remain in the relative safety and comfort of the surface control position. Gas supplies are limited only by what is available at the control position, and the diver only needs to carry sufficient bailout capacity to reach the nearest place of safety, which may be a
diving bell or lockout submersible. •
Saturation diving is a procedure used to reduce the high-risk decompression a diver is exposed to during a long series of deep underwater exposures. By keeping the diver under high pressure for the whole job, and only decompressing at the end of several days to weeks of underwater work, a single decompression can be done at a slower rate without adding much overall time to the job. During the saturation period, the diver lives in a pressurized environment at the surface, and is transported under pressure to the underwater work site in a closed diving bell. == Ultra-deep diving ==