Underwater Wakulla- April 14, 2011
Nitrox for Everyone By GREGG STANTON
Thursday, April 14, 2011 at 4:00 am (Updated: February 3, 11:27 am)
I have never understood why the diving community compartmentalizes Air (21 percent oxygen and 79 percent nitrogen) as a single gas
and Oxygen as a mixed gas. What then, do we call a mixture of AIR and oxygen?
Why, NITROX of course! So why would we want to breath Nitrox underwater, how safe is it and
how is it made? At a cost of only two cents more per cubic foot, there is good reason to consider
using Nitrox.
If I gave you a pill for your gas tank that doubled your vehicle's miles per gallon, would you be
interested -- even if you needed to watch the temperature gauge more closely?
Sure, because you get more miles for the cost of the same fuel. Nitrox does that for us divers and
a lot more. By reducing the nitrogen in our breathing mixture from 79 percent down to as low as 60
percent (the most common blend has 68 percent Nitrogen) you increase your allowable no-stop
bottom time, depending upon the blend and depth, up to three times that of Air.
Gregg Stanton
At a depth of 60 feet, I can blend you a 38 percent Nitrox that will give you 200 minutes on a USN
dive table!
But there is so much more: by breathing less nitrogen during the dive, and diving less than the maximum permitted bottom time, you
are less tired after a dive, can spend less time between repetitive dives, and still have more time at depth than when breathing Air. So
there must be a catch somewhere, and there is.
The oxygen in Air becomes toxic at 214 feet for most people, but long before you get there, narcosis (feeling drunk because of the
nitrogen) interferes with our resolve.
If we breathe mixtures with greater than 21 percent oxygen while diving, we find that toxicity at shallower depths. Predicting these
depths is a matter of math, something diving computers are good at. The greater the concentration of oxygen in the mix, the shallower
the toxic depth becomes, right up to 20 feet, beyond which you cannot breathe 100 percent Oxygen. We restrict recreational use of
Nitrox to no greater than 40 percent and compute the toxic depth, which is posted on the cylinder (MOD=maximum operating depth).
Follow the rules and the gas is relatively safe. Safe, as you may recall, means without risk.
The greater risk is in the blending of the gas, so don’t try this at home or you may burn your house down. Oxygen is a very reactive gas
in its pure form, so care must be followed when mixing it with Air. The air must be free of hydrocarbons (a petroleum lubricant found in
many diving compressors). Blending must be done slowly so as not to overheat the mixture until it is at its target blend. Calculations
are required to get the correct blend since Air also has oxygen in it. And of course, the gasses must be pure enough for human
consumption, which means lots of filters and testing.
A radical alternative Nitrox blending technique is to just remove the nitrogen from Air. This requires multiple compressors, gas
separating filters and storage cylinders which increases the cost of the gas, but on a boat where there is no other source of oxygen, is
a wonderful alternative.
So how do I get Nitrox?
Simple: get training to use it and purchase it from a reputable supplier. We offer a single day Nitrox training class where all these
details and many more are discussed. Our Nitrox costs two cents more than Air and requires no further alterations to your equipment
than a NITROX sticker on your cylinder.
Our Nitrox is on tap so it is dispensed upon demand from large flasks of pre-mixed blends. Many take this class as a refresher to
update their diving knowledge since we must also teach decompression theory considering how much less you will need to do.