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Chapter 43
- 3
THE TECHNICAL DIVE
1.
DIVE PROTOCOLS, PROFILES and GAS MIXTURES
2.
EQUIPMENT COMPLEXITY
3.
PHYSIOLOGICAL ASSUMPTION
— EAD / 0
2
/ C0
2
/ INERT GAS TRANSFER
4.
ENVIRONMENTS
5.
ACCIDENT & RESCUE IMPLICATIONS
1. DIVE PROTOCOLS, PROFILES and GAS MIXTURES
The diver attempts to select the theoretically ideal gas mixture for the ascent and descent (travel
mixes), the bottom (bottom mix) and the decompression staging (usually oxygen or a high oxygen
mixture).
The simplest form of technical diving has the diver breathing a mixture of 32% or 40% oxygen
(O2) in nitrogen (N2). With the increased O2, there is proportionately less N2. That means less
decompression obligation (and less N2 narcosis). For the same decompression risk, the dive can
therefore be prolonged and this is highly desirable in some dive trips. The additional risk of oxygen
toxicity must be appreciated.
Using a single O2 enriched gas mixture limits the technical diver to shallower dives than with
compressed air. A series of gas mixtures in separate cylinders, with diminishing O2 percentages,
allows the technical diver to reach greater depths. Substituting helium (He) for N2, either in Heliox
(He/O2) or Trimix (N2/He/O2) allows the technical diver to descend further, while avoiding or
reducing N2 narcosis. During ascent the changes of gas mixtures is reversed until nearing the
surface, when higher O2 percentages may be breathed to expedite the elimination of inert gas (He
or N2).
When there are various gas mixtures being breathed, the safe profile of the dive may be very
complex and errors may be made in the choice of gas breathed. Nevertheless, using open circuit
equipment and several gas mixes, dives to over 100 metres have been safely performed.
The use of rebreathing equipment enormously increases the potential hazards (see later), while
attemting to control and monitor the gases breathed and thedecompression required..