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Disadvantages of Nitrox

If there were only advantages to diving Nitrox there would be no need for a course. We would just have our tanks filled with Nitrox and go diving. So let's take a good look at the disadvantages.

First we must remember that Nitrox is a gas and thus we still have to equalize while descending and breathe continuously while ascending. And since Nitrox still has Nitrogen in it, it is still possible to get decompression sickness when diving Nitrox.

However, the real disadvantages of Nitrox are a result of the additional Oxygen in the mix. Specifically, the risks due to increased Oxygen concentrations in the mix are Oxygen Toxicity, Wrong Mix, and Trauma.
  

Oxygen Toxicity is, with out a doubt, the number one risk associated with diving Nitrox.

The more Oxygen in a mix, the less deep the mix can be dived. Each mix has it's own Maximum Operating Depth (MOD). The National Oceanic and Atmospheric Administration (NOAA) MOD's for various mixes are shown in the table below.
  

NOAA Maximum Operating Depths
	Air	NI or EANx32	NII or EANx36	EANx40	Pure Oxygen
Oxygen %	21%	32%	36%	40%	100%
Nitrogen %	79%	68%	64%	60%	0%
MOD	218 Feet	132 Feet	113 Feet	99 Feet	20 Feet

The high Oxygen concentration will cause the diver to have a gran mal seizure similar to an epileptic fit. On the surface, such an occurrence would result in unconsciousness but not death. Underwater, the diver will become unconscious, probably spit their regulator out, and drown. This event is essentially non rescueable. Attempts to replace the regulator and get the diver to breathe will not be successful. The only possible rescue would be to surface the diver immediately and treat for near drowning Clearly, the proper course of action regarding Oxygen toxicity is prevention.
  

Wrong Mix is the term applied to diving the wrong Nitrox mix for a particular dive. Some examples follow.

• Failure to measure the mix or properly mark the tank contents label with the Oxygen % and/or MOD can obviously result in using the wrong mix. If you aren't sure of the tank contents, you can't be sure of the safe use of the tank.

• Misuse could be deliberate. You have two EANx40 tanks (MOD 99 feet). You plan to dive two 60 foot reef dives but the dive plan is changed to a 132 foot deep wreck dive followed by a 60 foot reef dive --- you decide to do both dives anyway.

• Misuse could be accidental. You have two tanks one EANx32 (MOD 132 feet) and one EANx40 (MOD 99 feet). You plan to use the first tank on a 132 foot deep wreck dive and the second tank on a 60 foot reef dive --- but you don't pay attention when setting up your equipment and you dive the EANx40 mix on the deep wreck dive.

The result of diving a wrong mix can be diving a mix with more or less Oxygen than planned. If there is more Oxygen in the mix the result could be Oxygen toxicity and death. If there is less Oxygen in the mix the result could be decompression sickness. Either way, you loose.

Trauma or the injury from fires and/or explosions is always a possibility when working with Oxygen. Due to the relatively low concentrations used by recreational divers i.e. 40% maximum Oxygen, there is little risk to the diver. The risk is greater in dive stores that blend 100% Oxygen with air to make Nitrox. Fortunately, this is a controlled setting, and to date, dive stores vending Nitrox have a perfect safety record.

Two other disadvantages of diving Nitrox are limited availability and increased cost. While availability is getting much better, there are still places in the world, and even the United States, where only air is available. As to cost, Nitrox fills will always cost more than air fills due to the increased labor, material, and capital costs required to make Nitrox. Typical fill costs in South East Florida are $4.50 to $5.50 for air fills and $7.50 to $9.50 for Nitrox fills.

Note: To date, there has not been a single death due to use of Nitrox in a recreational setting. This is a direct result of recreational divers being properly trained in, and respectful of, the use of Nitrox for recreational diving.
  

Disadvantages of  Nitrox
Self Test

What is the  primary disadvantage to consider when diving Nitrox?

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