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Chapter 43
- 5
For the same depth/duration dive, the O2 enriched diver may have less DCS risk and less
N2 narcosis, but he will have more risk of O2 toxicity, than the air breathing diver. There
are the physiological implications of breathing oxygen at varying partial pressures, as well
as increased carbon dioxide retention with both increased oxygen diving and deep diving.
Inadequate factual information is available regarding the physiological interactions of multiple
gases. The rate of inert gas transfer between the breathing gases in the lungs, the body tissues and
any gas spaces (including decompression bubbles) varies both with the gas and the depth. Thus the
selection of different gas mixtures is likely to influence the transfer of inert gases in many ways,
far more complex than can be deduced from a simplistic formula. Anyone who doubts this should
peruse one of the more sophisticated texts on such topics as nitrogen narcosis and the counter
diffusion of gases.
Decompression procedures and algorithms are often unproven. Even with the vast data available on
air diving to 40 metres, there are many inexplicable decompression accidents. Adding the vagaries
of extended depths and durations, multiple gas mixtures and computer modelling, makes for
greater uncertainty in technical diving. Technical divers should question the origin and validity of
the decompression schedules they are encouraged to use. Some have had to be altered to reduce
their incidence of DCS. The lack of controlled trials have caused some to compare the promoters
of these decompression protocols to a pharmaceutical company marketing a drug without testing it
and then expecting the consumers to determine the correct dosages.
4. ENVIRONMENTS
The main purpose of technical diving is to extend the environments into which diving is
performed. This usually results in an increase in the hazards associated with such environments.
The exception is a reduction of the N2 narcosis of deep diving, by the substitution of helium. Most
of the other problems with deep diving are aggravated. Not only can the depth or duration of the
dive be extended, but so can the actual diving terrain. This is the reason why many wreck divers
and cave divers have embraced this activity.
5. ACCIDENT & RESCUE IMPLICATIONS
For the above reasons, the mixed-gas diver often wears a large amount of equipment, complex and
bewildering (especially when problems develop during the dive). The likelihood of superimposed
equipment problems is thus compounded. Difficulties include those of buoyancy and entrapment.
Depth control requires greater discipline and skill as the margin between the "safe" depth and the
oxygen toxicity depth, is much reduced. Sometimes a full facemask is indicated so that drowning
becomes less likely and rescue more possible.
Because of the different equipment and gases, and the extension of the environments, the
procedures for accident management and rescue may have to be altered to take into account the
specific problems – such as difficulty in removal of heavy and cumbersome gear. With each
variation from the conventional scuba system, there is a price to pay, and a possible modification
of the first aid and treatment procedures.