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Fri Jan 18, 08 01:55 PM
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diving
Deep diving
The meaning of the term deep diving is defined by the level of the diver's diver training, diving equipment, breathing gas, and surface support:
There are particular problems associated with deep dives:
- High gas consumption. Gas consumption is proportional to pressure - so at 50 metres / 165 feet (6 bar) a diver breathes 6 times as much as on the surface (1 bar). Heavy physical exertion causes even more gas to be breathed.
- Increased nitrogen narcosis. This causes stress and inefficient thinking in the diver. When breathing air many divers find 40 metres / 130 feet a safe maximum depth.
- The need to do decompression stops increases with depth. A diver at 6 metres may be able to dive for many hours without needing to do decompression stops. At depths greater than 40 metres / 130 feet, a diver may have only a few minutes at the deepest part of the dive before decompression stops are needed. In the event of an emergency the diver cannot make an immediate ascent to the surface without risking decompression sickness. The diver needs a disciplined approach to planning and conducting dives and needs to carry extra gas for the decompression stops to reduce the risk of being unable to complete the stops.
- Drifting. If long decompression stops are carried out in a tidal current, the divers may drift away from their boat cover or a safe exit point on the shore.
- Increased breathing effort. Gas becomes denser and the effort required to breathe increases with depth.
- Increasing risk of carbon dioxide poisoning.
- Oxygen toxicity
There are several solutions to these problems:
- Carry larger volumes of breathing gas to compensate for the increased gas consumption and decompression stops.
- Rebreathers are much more efficient consumers of gas than open circuit scuba.
- Use helium-based breathing gases such as trimix to reduce nitrogen narcosis and stay beyond the limits of oxygen toxicity.
- A diving shot, a decompression trapeze or a decompression buoy can help divers return to their surface safety cover at the end of a dive.
Blenheim Bomber - Malta
This is a fabulous dive. The aircraft quickly begins to take shape as you descend. The wings and engines are virtually intact although the port side propellers are missing. The cockpit cover has also disappeared and this might suggest the crew safely evacuated prior to ditching. The pilot's seat and control column are quite intact and altogether these aspects form the main section. The fuselage is detached and lies upside down a few metres to the front - mostly buried. In fact, it night not be recognised at all were it not for the single, non-retractable stern wheel which now sits upright and proud of the seabed - still occupying the extreme rear end of the aircraft. Altogether this allows divers to independently explore and inspect the entire area of the wreckage without getting out of sight of their buddies. The main wheels - retracted during flight, are still to be found on the underside of both wings still in that retracted position. The engine covers have long gone thus enabling the diver to inspect the main parts that made up this type of 920 hp Bristol Mercury engine. The control lever is directly in front of the pilots seat and there is always a temptation for the diver to sit in the seat for a brief moment of fantasy. In this case, however, the seat is very small and any such temptation should be avoided at all costs because all the diver will achieve is to break the seat from its rather delicate mounting.
This is a deep dive at 42 meters so special care and training must be taken into consideration.
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Link:
http://blog.bitcomet.com/post/14567/
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