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Gear Meister answers your gear questions...

Staying Power - a reason to "Get Gassed"

Over the last few months, we talked about regulators. In your regulator search, perhaps you came across the phrase “NITROX compatible.” What does that mean and how could it effect your purchase? To answer that, we need a few sentences of technical discussion and a quick review of decompression theory.

As you recall, there are really only two things that determine how long we can stay down at a given depth in recreational diving – how long the gas in our cylinder lasts, and how much nitrogen we absorb. Bigger and more tanks solves the first problem. Altering our breathing gas solves the second.

 

The normal air that we breathe is roughly 21% oxygen and 79% nitrogen. Our body uses the oxygen to feed our cells. Nitrogen, on the other hand, can’t readily be used by our bodies for fuel. Instead, it is stored in our cells and can cause problems with decompression illness when we surface. At depth, the greater pressure surrounding our body forces more nitrogen into our cells at a faster rate than on the surface. It is this stored nitrogen that limits the amount of no decompression time we can spend at depth. The greater the depth, the greater the rate at which nitrogen is absorbed by our body, and the less time we can stay down before we reach our no decompression limit. That’s why we can stay at a shallow depth for a long time but only a short time at deep depths.

NITROX, also known as Enriched Air Nitrox (EAN), was designed to reduce the amount of nitrogen that our body absorbs at depth and thereby increase our bottom time before reaching our no decompression limit. Nitrox is made by removing some of the nitrogen from the air and replacing it with additional oxygen. For example, a common Nitrox mix is EAN-32, or 32% oxygen and 68% nitrogen. Our body simply uses the additional oxygen as it normally would. But since there is less nitrogen in the mix to begin with, there is less for our body to absorb, and we get to stay down longer. For example, a diver breathing normal air on a dive to 100 feet (33m) is limited to 20 minutes. Breathing EAN-32, that same dive is safely extended to 30 minutes. So you can see the benefit of using NITROX.

Too much of a good thing...
But, if it’s so good, why don’t we use it all the time? Or why don’t we get rid of all the nitrogen and replace it with 100% oxygen.? There are some negatives to using NITROX. One major reason is that a given percentage of oxygen will become toxic at a certain depth, causing vision problems and seizures. The greater the percentage of oxygen, the shallower the depth at which  it becomes toxic. So, depending on how deep you want to go, you may not be able to use NITROX at all.  Or the ratio will be so little changed from regular air, that the benefit is marginal. This oxygen toxicity hazard is why a diver should never use NITROX unless they have first been trained in how to safely use it.

Equipment hapzards

Another hazard associated with oxygen affects our equipment. High concentrations of oxygen are extremely flammable, even explosive. High concentrations of oxygen can be ignited by coming into contact with petroleum products, certain kinds of rubber (as in o-rings), or other contaminants in the cylinder or other equipment. For recreational diving, the oxygen limit has been restricted to 40%. Most scuba regulators (first stage, second stages, and SPG) made today - 1995 and later - are made to be compatible with oxygen concentrations up to 40% and will include a statement on the box to that effect. If a new regulator set doesn’t specifically state that it is NITROX compatible, it may not be and could present a fire/explosion hazard. Regulators made before 1995 may or may not be compatible and you should check with the manufacturer for guidance.

You may also see some regulators that are NITROX compatible above 40%  - all the way up  to 100%. These are for technical diving and far beyond the scope of what you will use in recreational diving. And no, more is not better. These regulators have greater care and maintenance requirements that cost you extra money.

Plan ahead
Do you really need your regulator to be NITROX compatible? Even if you’re just getting started in diving and can’t even see yourself using some “voodoo” gas, it’s very likely that you may change your mind later on. Recreational NITROX is very useful, safe, and available if you get proper training. Even if it were to cost a few dollars more to purchase a compatible regulator, it would be worth it in the long run rather than have to rent or buy a second reg just to use NITROX.

"Mo' better"
Of course, using NITROX can’t help you stay down longer if you run out of gas in your cylinder - that only gets better with practice. The more you dive, the better you dive.