There exists a number of glaring misconceptions regarding the usage of nitrox in scuba diving. Nitrox use may not be as safe as what a number of recreational divers proclaim. Responsible divers should understand the risks and limitations involved if they intend to try mixed gas in recreational deep sea ventures.

If you are confused about the current nitrox controversy, don’t feel alone. It is not easy to wade through the complicated claims and counterclaims about this unorthodox form of diving.

There has been so much ballyhoo from nitrox purveyors and promoters that it is hard to separate fact from hyperbole. Is nitrox as safe as they say? Is nitrox the miracle gas for recreational divers? Are divers really going to be able to double their bottom times?

We are going to examine many of the statements made by nitrox proponents and some of the puffery stated in nitrox diving ads – and tell the other side of the story. Let’s compare their claims to the facts, as we know them. For the sake of clarity and simplicity, we are going to omit as much of the physics and physiology as possible. This is plain talk about the pros and cons of the nitrox controversy.

Nitrox miracle gas or double jeopardy

Pros And Cons

PRO Nitrox is the “hot” new breathing gas for scuba diving.

CON Not true. Nitrogen/oxygen mixed gas diving has been around for more than 40 years. Experimentation with nitrox mixtures dates back to the early days of hardhat diving. This gas has been used by the U.S. Navy and commercial divers for shallow water work. They regard nitrox as just another mixed gas with limited application.

The important difference is that commercial and military divers use nitrox in a much different way than recreational divers use scuba. Mixed gas diving requires a large surface support team to assist the diver and affect an immediate rescue when something goes wrong.

Commercial/military divers wear a hardhat, bandmask or full facemask to create an envelope of breathing gas around their faces, if they blackout from too much or too little oxygen, they will not drown. These divers are connected to the surface by a tether, so they can be pulled up if blackout occurs. A dive tender on the surface handles the tether. The diver is also connected to the surface by a hardwire communications link – a two-way telephone. On the surface, a deck decompression chamber is on standby, ready to treat any accidents. All of this equipment is designed to reduce the risk involved with nitrox or any other mixed gas diving. These safety procedures have evolved over a 100 year period of trial and error.

The scientific/harvesting diving community does it differently. Much of its work is conducted in waters that are no deeper than 60 or 70 feet. The shallow depths provide a safety net that prevents the diver from getting too near the red line for oxygen toxicity.

PRO Air is nitrox.

CON Not true. Air is the natural composition of gases found in the earth’s atmosphere. For practical purposes, this composition is generally described as 79 percent nitrogen and 21 percent oxygen. The actual composition is much more complex: 78.084 percent nitrogen, 20.946 percent oxygen, 0.934 percent argon, 0.033 percent carbon dioxide and 0.003 percent rare gases (neon, helium, krypton, hydrogen, xenon, radon and carbon monoxide). Human beings have evolved breathing this mixture for the last few million years and no one really knows what role carbon dioxide and the other trace gases play in diving with compressed air.

Unlike air, nitrox can be any one of a dozen different artificial compositions utilizing a nonstandard mixture of oxygen and nitrogen. Two of the more common ratios are: 32 percent O2~, 68 percent N2~ (NOAA Nitrox I) and 36 percent O2~, 64 percent N2~ (NOAA Nitrox II).

Each nitrox mixture or blend requires its own set of tables and bottom time limits.

PRO Air is a bad gas for scuba.

CON Not true. Compressed air has been used by commercial and military divers for hundreds of years. This precedent was adopted by sport divers; compressed air has served recreational diving very well for the last 50 years. Despite its increase in popularity, the number of annual diving fatalities has been decreasing over the last three decades.

The number of scuba fatalities among U.S. citizens for 1990 totaled 91 deaths. This figure is much lower than the prior year, when there were 114 fatalities. It is dramatically less than 1976, when the number of scuba fatalities reached an all-time high of 147.

PRO Nitrox is enriched air.

CON A clever play on words. If air is “enriched” by the addition of oxygen, it is no longer air. The resulting blend is a mixed gas – artificially mixed. Nitrox can be manufactured several different ways. One way is to mix pure oxygen with pure nitrogen to obtain the precise percentages and then compress the gas to a higher psi.

The alternate and more popular method is to simply empty a scuba tank and then bleed into it a certain psi of pure oxygen. Compressed air is then added to the tank to top it off. Theoretically, the resulting fill should be approximately the correct “enriched air” nitrox mix (NOAA Nitrox I). This “home brew” approach (not endorsed by nitrox agencies)is less expensive but much more hazardous. Pure oxygen is highly flammable and the scuba tank receiving it must be scrubbed clean of any residual oil micro-particles.

PRO Nitrox is a safer diving gas than air.

CON Not true. Nitrox advocates claim this gas is safer than air because of the longer bottom times and less risk of decompression sickness (bends). What they fail to mention is that nitrox presents a whole new set of problems with a high risk of oxygen toxicity.

Bends generally cause pain and sometimes paralysis – but death is rare. On the other hand, the symptoms of oxygen toxicity are generally seizures, convulsions and unconsciousness – often leading to drowning and death.

Incidentally, nitrox diving does not eliminate the risk of decompression sickness. You can still get the bends by staying down too long, coming up too fast, bypassing a required decompression stop or accidentally using the wrong nitrox mix or nitrox tables.

PRO More divers get bent using air than using nitrox.

CON The above is a misleading statement. Of course more divers get bent on compressed air than nitrox – a lot more people are diving with air. The number of certified nitrox divers is estimated to be 4,000 to 5,000. The number of certified recreational divers is estimated to be 1.5 million!

PRO Nitrox doubles your bottom time.

CON Not quite the whole story: True, a certain nitrox mix will almost double your allowable no decompression bottom time, but let us examine this statement a little more closely.

According to the NOAA decompression tables, NOAA Nitrox l will allow a diver to spend 200 minutes at 50 feet. But wait a minute, a single 80 cubic foot tank will not carry sufficient gas supply to last 200 minutes (3 hours, 20 minutes) at that depth! The average diver would be lucky to stay down 70 minutes.

This means you would have to wear doubles – twin 120s or 100s in order to get your money’s worth. Packing 100 pounds of scuba tanks around is not fun – it is hard work. Wearing double tanks on a rocking boat is no fun. Swimming with doubles underwater requires much more exertion to overcome the additional drag. Physical exertion underwater is one of the major triggers for oxygen toxicity (even when you are well within theoretical safety limits).

For the average recreational diver, bottom time limits are as much a function of gas (or air) supply as no decompression limits. The tank starts running low just about the time your computer (or tables) indicates it is time to come up anyway.

You could say that nitrox doubles your bottom time but it would be more accurate to say it doubles you bottom time if you are willing to double your tanks, double the weight on your back and double your hassle. As for the risk, it more than doubles as well.

PRO Oxygen toxicity is not a problem if you stay within the prescribed limits.

CON This is not necessarily true. Susceptibility to oxygen toxicity is widely variable, depending upon the individual. The mechanism for this type of poisoning is not fully understood.

Many factors can contribute to oxygen poisoning such as: excessive depth, decrease in core temperature, duration of exposure to high partial pressure of |O.sub.2~, physical exertion underwater and C|O.sub.2~ buildup. You could be within the nitrox table limits and still suffers a seizure.

Oxygen toxicity comes on without warning, causing an epileptic-type seizure and unconsciousness. This rapid series of events often leads to death by drowning.

PRO Nitrox expands your diving capabilities.

CON Nitrox is actually more restrictive. Nitrox diving is restricted to a very narrow sector of operation. Overstep the boundary and you could experience a sudden seizure and die.

Let’s make a simple comparison. NOAA Nitrox I has a red line limit of 132 feet and NOAA II has a limit of 113 feet. Compressed air has a red line limit of 130 feet for nitrogen narcosis and a 231 foot limit for oxygen toxicity.

If you exceed the compressed air red line limit of 130 and dip down to 140 feet for a minute or so – nothing drastic is likely to occur. You might feel a little decompress. This is not an example of a good dive profile but it happens to many recreational divers.

Try the same sort of thing with nitrox and you could end up dead. Oxygen toxicity is cruel and unforgiving. Descend five feet below the red line and you might wipe out. There is seldom any warning from this silent killer. One minute you are swimming along just fine; the next minute you are caught in the death grip of an uncontrollable seizure. The seizure leads to blackout and drowning. If your dive buddy doesn’t happen to be looking your way, you are out of luck.

PRO Nitrox training will keep you safe.

CON Wrong. Strict discipline ensures safety – not training. Like all mixed gas diving, nitrox has a narrow safety margin and there is deadly risk if you deviate from the rules. Training may help you understand the problems and risks but only strict diving discipline can help reduce them.

It is this issue of self-discipline that separates the professional from the recreational diver. Professional divers stick to the rules – or they are fired. Recreational divers (as east some of them) bend the rules.

PRO Nitrox is the end-all solution for scuba.

CON Not true. Nitrox is only the beginning. Divers who start diving with nitrox soon discover they are very limited. They cannot go any deeper than 132 feet. Yet, once introduced to mixed gas diving they are easy converts for trimix – an even more dangerous practice. This year alone, trimix diving has caused the untimely deaths of a number of recreational divers.

PRO Nitrox diving is being accepted by everyone.

CON Not true. National scuba training/certification agencies such as PADI, SSI, NAUI, PDIC and YMCA will not touch nitrox training or certification. They have all backed away from this high risk activity. Nitrox promoters had to form their own training and certification agencies.

DEMA issued a public statement that nitrox may not be compatible with standard scuba equipment. Regulator manufacturers such as U.S. Divers have started enclosing a warning card in every regulator box, stating their regulators are designed for compressed air and should not be used with nitrox or other mixed gases.

PRO Enriched Air Nitrox (EAN) will be available at every dive shop.

CON Not every dive shop can pump nitrox. Pure oxygen can be dangerous and explosive if it comes in contact with oil or oil products. This is called ”flashing.” Many dive shops have oil lubricated air compressors that are not compatible with oxygen filling safety rules. The risk of an explosion or fire while handling nitrox is much greater than with non-flammable compressed air.

PRO Nitrox is here to stay.

CON No one can say for sure. Nitrox diving for recreational purposes is in its infancy. There are an estimated 5,000 nitrox divers in the U.S. – maybe a few more. It could be a fad that sputters out because of the limitations and hazards. A large wave of nitrox diving accidents and deaths could stop it cold. It could be banned by governments who feel need to protect the public.

PRO The era of single mix technology is over.

CON Wrong. Compressed air has been around for centuries and it will continue to be the breathing gas of choice for recreational diving. Millions have used it and lived. It is simple to produce, easy to handle and perfectly safe when used as prescribed.


Like any controversial issue, nitrox has a bright side and a dark side. Nitrox advocates will always present the bright, shiny side with claims of safer diving, longer bottom times and no need for decompression. In addition, there is the built-in excitement and appeal of trying something new. We have presented the dark side – all the limitations and hazards.

It will be up to you, as a mature, informed individual, to decide whether you wish to take on the added risk nitrox represents.

At present, there is no law prohibiting mixed gas use by recreational divers. You may wish to check the fine print of your life insurance policy though – it may not cover this kind of thing.

The point is, you and you alone must decide whether you want to try this high risk diving gas. Are the benefits worth it?


Air: The natural gas of the earth’s atmosphere – composed of 78.084% nitrogen, 20.946% oxygen, 0.033% carbon dioxide, 0.934% argon and 0.003% rare gases.

ANDI: Acronym for the Association of Nitrox Divers, Inc – a newly formed training and certification agency for nitrox diving.

EAN: Acronym for Enriched Air Nitrox, a mixed gas 30 to 50% oxygen.

EANx: Same as EAN, a mixed gas containing 30 to 50% oxygen.

Enriched air: A mixed gas consisting of compressed air to which oxygen is added so that it becomes a nitrox mix. Same as EAN or EANx.

Heliox: A mixed gas containing only helium and oxygen, no nitrogen.

Home brew: Nitrox mixed at home by recreational divers – depending on a mathematical calculation of gas pressures.

IAND: Acronym for International Association of Nitrox Divers – a newly formed training and certification agency for nitrox diving.

Nitrox: A breathing gas of variable mixtures that deviates from the standard compressed air mix of nitrogen, oxygen and trace gases.

NNI: Acronym for NOAA Nitrox I – a specific gas mixture of 68% nitrogen and 32% oxygen. This mixture specified by the National Oceanic and Atmospheric Agency (NOAA).

NNII: Acronym for NOAA Nitrox II – a specific gas mixture of 64% nitrogen and 36% oxygen. One of two standard nitrox gas mixtures established by NOAA.

Oxygen toxicity: An acute condition caused by too high a partial pressure of oxygen for too long, resulting in convulsions and unconsciousness. If this condition occurs during scuba diving, it can lead to drowning.

Technical diver: A newly invented term that describes a diver who engages in the practices of deep diving on compressed air, nitrox diving or trimix diving.

Trimix: A mixed gas containing oxygen, nitrogen and helium at variable percentages.

Nitrox Mixed Gas Diving Limitations And Hazards

1 Nitrox will not allow you to go any deeper than compressed air.

2 You cannot double your bottom time using standard recreational scuba gear (80 cubic foot tank and regulator).

3 The risk of oxygen toxicity outweighs virtually all possible benefits.

4 Bends causes pain and paralysis – oxygen toxicity causes seizures and unconsciousness, leading to drowning and death.

5 The present nitrox tables and depth limits may not be entirely safe for all recreational divers. Oxygen tolerance is widely variable, depending on the person, water temperature and physical exertion during the dive.


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