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Chapter 6 — 6
The problems centre on impaired visibility. Vision is dependent on artificial light which is very
restricted and can easily fail. It is important for the night diver to be able to find and use all
items of equipment by touch alone.
Detecting and rescuing divers who develop problems and surface some distance away, may be
difficult. An emergency flare, strobe light or chemical light stick (e.g."cyalume") attached to the
diver's tank valve is worthwhile carrying for this eventuality, as is a whistle.
Deep Diving
Dives deeper than 30 metres have an increasing number of complications, possibly with
inappropriate responses to these.
The endurance of the scuba air supply is severely limited at greater depths while the
decompression requirements increases almost exponentially, adding a sense of urgency to the
dive in the face of a diminishing reserve-air safety margin.
Decompression stops become obligatory for even short dives to depths in excess of 40 metres
and requires the provision of extra air for this purpose. Unfortunately, the decompression tables,
even if followed exactly, become less reliable as the depth increases, raising the possibility of
serious decompression sickness even after a faultlessly executed dive.
Nitrogen narcosis can occur at less than 30 metres (100 feet) and progressively impairs
judgement, attention, perception and an appropriate response to adversity as the depth increases.
At depths in excess of 45 metres (150 ft.) mental stability, cognition and judgement are seriously
impaired. See Chapter 18)
Equipment becomes more difficult to manage at these depths. Breathing through the regulator
becomes harder. The buoyancy compensator takes much longer to inflate and uses more of the
limited air supply. Wet suit compression reduces its insulating properties at the same time as the
diver passes into colder deep water. This compression also progressively decreases buoyancy.
The environment beyond 30 metres is dark, colourless, cold, relatively devoid of marine life
(although the fish and sharks are often larger), and replete with physiological hazards. In spite of
this, some recreational divers feel compelled to experience it, albeit briefly because of the
limited air endurance.
The authors recommend that, in view of the increased hazards and the limited diving satisfaction
available in deep dives, recreational divers regard 30 metres (100 ft.) as the maximum
recommended safe depth. Uneventful dives beyond this depth often impart a false sense of
capability – which is then shattered when one or more things go wrong. It is then that the effects
of narcosis are demonstrated.