Nitrox Specialty Class

Prerequisites: Advanced Open Water
To be a Nitrox Diver you will need to take the Nitrox Specialty Class offered by Get Wet Scuba Divers. The Class requires a book, DVD, One Class Room Session and Two Dives. In general the classes are small so the Instructor(s) can focus on giving you quality supervision to make sure you understand the benefits and limitations of Nitrox mixtures. Although you can figure out the math for Nitrox before you dive, you might want to consider getting a computer that can calculate itself.

About Nitrox
Nitrox has become a common term in recreational diving. Nitrox is a mixture of Nitrogen and Oxygen in different percentages. The two most common mixtures are 36% and 32%. Tech Divers will usually go over the 40% mark for recreational diving mixtures.

Benefits of Nitrox
In short, the correct nitrox mix can be safer than air for the diver and requiring less decompression time. However, we need to qualify that; by correct I mean the most appropriate mix for your dive and it's safer provided you follow the guidelines for its use.

Nitrox provides faster off-gassing than air during decompression. It may be used to reduce the length of the decompression penalty by following a nitrox decompression schedule, or it may be used as padding to increase the safety factor by following an air decompression schedule. This is similar to the use of pure oxygen during decompression.

Limitations or problems using Nitrox
Bear in mind the risk of acute Oxygen Toxicity with Nitrox is no greater than that with air. The difference is the changed priority between Nitrogen and Oxygen. On Air, Nitrogen Narcosis is generally the governing factor in choosing a maximum depth for most sport divers.

Reports
A considerable amount of Nitrox users have commented about how refreshed they feel after using Nitrox while Scuba Diving. I the Editor (Avid Scuba Diver ) of this content can vouch for this unusual feeling of refreshment compared to normal air dives.

How long has nitrox been around?
Quite a while. The early history of nitrox is really the history of research into oxygen toxicity.

The toxic effect of enriched oxygen mixtures were first demonstrated by Paul Bert in 1878. He discovered that high partial pressures of oxygen were directly responsible for causing convulsions.

In 1899, Lorrain Smith demonstrated that animals breathing moderately increased partial pressures of oxygen over a long period develop pulmonary problems. For example, a partial pressure of about 0.8 bar breathed for more than 4 days produced severe lung problems and could be fBarl. In 1903, Hill and Macleod noted that resistance to pulmonary damage in individuals varied enormously.

Between 1910 and 1912 various experiments were carried out using nitrox including riding a bike while breathing nitrox10 and a dive to 100 fsw (30 msw) using a surface supplied 50:50 nitrogen-oxygen mixture. These may have been the first experiments in which the effects or nitrox were observed in man.

During the 1930's a great number of experiments were carried with individuals breathing PO2's in the range of 2 to 4 Bar - even one of breathing up to 7 Bar (Haldane (the younger) in 1941). When taken overall these experiments demonstrated the enormous variation in susceptibility. Some people were okay after an hour while others convulsed within minutes. One even convulsed after switching back to air (which he did because his lips were twitching). In 1933, Shilling and Adams noted the extreme variation in CNS O2 toxicity tolerance although they erroneously concluded that man should have ample warning of the onset of symptoms. It was discovered that prior to the onset of CNS O2 toxicity there is a loss of respiratory control where breathing may become jerky and irregular and then change to become prolonged and laboured. They also noted that the effect varied enormously between individuals. In 1939, Lambertson developed the first nitrox rebreather.

In Haldane's experiments some subjects said they could taste the oxygen at 5 to 7 Bar. Dr Kenneth Donald, author of Oxygen and the Diver, breathed O2 at 10 Bar for 25 to 30 seconds along with Haldane and another man. Only Haldane thought he might have tasted something.

Experiments with cats in 1944 showed that repeated CNS O2 hits produced symptoms similar to that of neurological damage but the effects apparently disappeared a few weeks after the exposures were stopped. The cats also appeared to develop a tolerance to the high partial pressures during the experiments but this also returned to normal after a few weeks break.

Between 1942 and 1945 the Royal Navy carried out extensive work on oxygen poisoning in divers. The experiments are documented in Kenneth Donald's book. His conclusions were that diving on pure O2 deeper than 25 fsw (7.6 msw) is a pure gamble. He found that tolerance is reduced underwater (compared to dry experiments) and that the variation in symptoms, even for the same person, makes the onset impossible to predict.

In the 1950's Rev Lanphier worked on producing O2 exposure tables for the US Navy. He reached many of the same conclusions as Dr Donald but there were some discrepancies. Despite experimental evidence from Dr Donald's experiments to the contrary, Rev Lanphier concluded that oxygen was more toxic when breathed as part of a nitrox mixture. Experiments by other researchers have supported the conclusion that nitrogen has no effect on oxygen toxicity. However, Lanphier's conclusions were the basis of the US Navy's exposure tables in 1959, and for many years after that.

Rev Lanphier also tried to find a way of predicting CO2 retainers but could not find one. He realised that breathing resistance at depth, due to higher gas density, may increase CO2 levels. A higher CO2 level in the body would increase the risk of O2 toxicity, however, the fact that divers are breathing out an increased level of CO2 cannot be used to infer the arterial and body CO2 levels. Thus it does not immediately follow that nitrox divers are at an increased O2 toxicity risk due to CO2 retention.

The work to find out if divers adapt and become CO2 retainers continued through the 1960's and is still continuing today. Dr Donald's opinion is that there is no conclusive evidence that divers adapt and become less sensitive to the carbon dioxide breathing stimulus.

A major step was taken in 1970 when Dr Morgan Wells of the National Oceanic and Atmospheric Administration (NOAA) began experimenting with nitrox. He recognised the advantages of nitrox for the type of diving that NOAA divers were carrying out. Dr Wells was responsible for the (now) standard nitrox I (published in 1978) and nitrox II (published in 1990) mixes. It is largely as a consequence of NOAA's decision that we have nitrox in the recreational diving scene today.

Dick Rutkowski formed the International Association of Nitrox Divers (IAND) in 1985 to teach nitrox to sport divers. In 1992 the name was changed to the International Association of Nitrox and Technical Divers (IANTD). The T was added when the European Association of Technical Divers merged with IAND. Prior to founding IAND, Dick Rutkowski worked for Dr Wells and was director of the diver training at NOAA. This was the first organisation to offer international training to recreational scuba divers.

In 1987 or 1988 Ed Betts, who had previously been with Dick Rutkowski at IAND, formed the second organisation for recreational nitrox training: American Nitrox Divers Inc. (ANDI).