The Instructor's Corner (NITROX)

Hi Team,
After multiple conversations this week about the same topic (Enriched Air Nitrox Diving) I thought it would be useful to resurrect an old column  that we used to do back in the day of snail mail and actual paper newsletters, The Instructor's Corner.  These brief articles covered general knowledge and our techniques on topics such as local beach diving and how the pros do it, safe and general computer diving, practices, boat diving, spearfishing and so on.  Some of these articles have even been published in the past like Beth's mask clearing made easy in Dive Training Magazine and Bryan's & Hugh's tip's from the pros in PADI's Sport Diver Magazine.

OK, first off I am not a physicist or anything of the like.  Matter of fact I am an artist so numbers and math are all goofy in my head anyway, but if I can learn this stuff anyone can.
If you are not Nitrox Certified then hop over to the e-Learning page and lets get er done.  
To truly understand Enriched Air or Nitrox Diving, you need training! This article is only a quick overview on Oxygen Management and a quick introduction to Enriched Air Diving. Do not attempt, in any way, to use this article or any of the construed advice as training. Do not dive Enriched Air unless you are certified and qualified to do so. That means a certified Enriched Air Scuba Instructor has signed off that you are trained to dive Enriched Air. Scuba diving is a great sport, but dangerous if you do not dive within your training limits.

Nitrox made Easy

If you need a quick review then check out this article.

Here is the skinny,
(As stated above this is not training so all of you tekkies and physics and physiology nerds keep your two cents to yourself, this is a basic discussion for basic use for beginner divers)

What is Nitrox and why is it good?

Enriched Air Nitrox is a mix of breathing gas that contains a higher percentage of Oxygen than normal air. Typically 28% to 40%, but anything higher than 21% can be considered "Nitrox".  The two most common mixes for our area of the Gulf is EAN28 and EAN32.  
The general idea behind Nitrox is that our bottom time is limited by the amount of Nitrogen we take in "on gas" and can "off gas" safely with our limited amount of time/gas.  So by removing some Nitrogen we should be able to stay down longer.  
This science is true with one added benefit.  A mix containing higher contents of Oxygen also requires less surface interval time in between dives as a similar air dive or you gain more credit toward your next dive in the fact that you absorbed less Nitrogen.  The added Oxygen also works to help "off gas" the absorbed Nitrogen faster.  Make since?  Think about it.  What is basic first aid for DCS (the bends)?  Oxygen, right.  So diving with extra oxygen in your breathing mix is kind of like checking both ways before you cross the street.  Don't get hit by a truck and go to the hospital and then later finish crossing the street.  Just don't get hit by a truck.  
Another great benefit is the highly increased bottom times for repetitive dives.  The lower amount of absorbed Nitrogen greatly increases the bottom time for dives two and three.  Sometimes tripling the adjusted bottom time.
More than one out of three divers claim to feel better and less worn out after a day of diving Nitrox.  There is no real scientific proof that such a small increase of Oxygen is not really enough to add other beneficial effects.
Lastly all the tekkie stickers look cool.  Just kidding. :}

Is it safer?

Erm, well, hmm, the general answer is no.  All of the same scary stuff that exists with breathing compressed air still exists when diving Nitrox.  
One way that it can be safer in our area (generally 100' dives) is that divers who have great air consumption rates have a bigger chance of accidentally going into "deco" when using larger volume tanks filled with air.  The extra time provided by Nitrox can help divers avoid this.  This is one reason that we see so many large volume tanks with Nitrox stickers.

What is bad?

Its not really bad but dive planning can be a little more complex in that you have to use the right mix for the right depth.  The more Oxygen in the mix the shallower you have to dive.  Nitrox is best when used 50' to 110'.
Then there is that Central Nervous System Toxicity thingy.  Yeah this is bad.  Rarely found in recreational divers CNS Toxicity can cause convulsions underwater.  "Not good, Mav."  
This happens when divers dive too deep on the wrong mix or dive too many repetitive dives exceeding or reaching maximum limits.  It's simple don't dive a dose above 1.4 pp02.  If you don't know what that means then take the class.   ***Click Here for Nitrox e-Learning***

Some divers push it by diving a dose of 1.6 ppo2.  This is not wise and is only to be used for contingency (emergency) planning or Deco for Tec Divers.  Not recreational diving.  After 45 minutes of high ppO2 (too deep for the mix) your chance of winning the CNS Toxicity lottery is almost 100%.  This is cumulative for every repetitive dive.  So in theory if you dive over a 1.4 ppo2 it could happen on one dive.  
(trust me I know) 
Look at the 1.6 ppo2 row at the bottom ==>NOAA Exposure Table  See?

The other down side is that it can be harder to get, so if you are diving out of a jungle hut don't expect the tank kid to use his bicycle pump to whip you up a batch of Nitrox. 
Not everyone can blend nitrox so you may have to wait for the blender to fill your tanks.
Also it's not cheap. It can cost up to three times the cost of an air fill.

How do I use it?

Order the right mix. (see your course materials for determining the "best" mix)
Analyze the blend yourself. Remember you are changing basic dive physics.  Trust nobody.
I only trust my analyzer so its a good idea to have your own.  We like the Oxycheq Expedition, its small, cheap, and easy to use.
Sign a nitrox log, label your tanks, check the maximum safe depth on your computer or chart and go diving.

Our general diving area makes it simple when it comes to choosing mixes.

You will find yourself either diving around a 100' (Navy Tug, Notch, Bridge Rubble, Liberty Ships, and Tanks) or 130' (the Oriskany, Trysler, Avocet) so diving here you only really need to be concerned with two mixes EAN32 and EAN28. (shoosh, tec divers, see above)

The best mix for depths up to 110' is 32% the MOD for 32% is 111'
The best mix for depths up to 130' is 28% the MOD for 28% is 131'

 Before posting remember this is a light hearted discussion about the Voodoo gas.

Thanks and be safe out there.