Diving with a large capacity Nitrox tank
Recreational scuba diving is all about enjoying the underwater world but within a variety of constraints. However divers who descend beyond 30 metres or extend their bottom time should have the appropriate training, equipment and experience so that the risks are minimised. The most well known forms of diving injuries are Decompression Illness (DCI) and Air Embolism though the incidence of these problems in recreational diving is relatively rare.
At the “SAFER LIMITS 2000”, Hyperbaric Workshop, held at the Wesley Hospital, Brisbane, September 2000, it became clear that diving is considered to be a very safe recreation these days compared with other adventurous activities. This opinion was based on the number of DCI cases treated in Australia compared with the total number of dives per year. One of the main reasons for this is that most divers now use a dive computer, rather than tables or nothing at all. It would seem that there is evidence to suggest that the use of the dive computer has made diving safer.
Diving fatalities due to an air embolism are rare but can result from a rapid ascent due to a serious problem known as an ‘out-of-air emergency’. Basic steps such as dive planning, buddy procedure, frequent monitoring of depth, time and air supply, should prevent these incidents from even starting. It is likely that the real cause of the problem is inadequate training and experience for diving at depth since the training agencies regard diving from 30 to 40 metres as ‘deep diving’.
Divers contemplating diving beyond the recreational limit of 30 metres should attend a comprehensive Deep Diver speciality course to learn the necessary skills and to use the additional safety equipment that should be used. In particular, this course should cover gas consumption at depth, and include at least four dives using safety equipment such as twin tanks, pony bottles, sling tanks, hang tanks, high performance regulators, reels, lift bags, etc. Although the larger tanks and/or secondary air supply will provide a substantial safety margin for diver or dive buddy, there is still the overriding no-decompression limit on bottom time.
Extending Bottom Time
Planned bottom time may be extended by using Nitrox (within its own limits) instead of air. Nitrox is oxygen enriched air, or air with a greater than normal percentage of oxygen. Divers who wish to use oxygen enriched air must attend a Nitrox Diver specialty course which should cover oxygen toxicity, partial pressures, nitrogen toxicity, dive planning, blending and analysing gas mixes. The use of Nitrox pushes you towards using better equipment and having a more disciplined approach to diving. As Bret Gilliam (TDI) says, using Nitrox is not technical diving, just safe recreational diving.
Typically Nitrox tanks are steel 12 or 15 litre cylinders with high-pressure DIN valves that are rated to 232 Bar. These days, new high performance regulators are either Nitrox-compatible or ready for Nitrox use, with a DIN or yoke first stage. A Nitrox dive computer can be set in the field for one or more gas mixes. The computer should have a depth alarm which should be set to the Maximum Operating Depth of the gas mix being used. An air-integrated Nitrox computer should display the remaining bottom time under unchanged diving conditions.
Further information is available in the Magazine section of this website.