Definition: Nitrox refers to any gas mixture composed of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases. The most common use of nitrox mixtures is when it contains oxygen in higher proportions than atmospheric air because the reduced partial pressure of nitrogen is advantageous in reducing nitrogen uptake in the body's tissues, thereby extending the practicable underwater dive time by reducing the risk of decompression sickness.
This definition seems fairly straight forward, however there are MASSIVE missunderstandings related to the use of Nitrox. Primarily because of the flippant use of terminology that confuses people.
Some of them are:
- Nitrox allows you to dive deeper = INCORRECT
- Nitrox allows you to dive longer = INCORRECT
- Nitrox is of no value above [depth] = INCORRECT
- Nitrox reduces post dive fatigue = INCORRECT
- Common air is not Nitrox = INCORRECT
- Nitrox is always a specific % of O2 = INCORRECT
- Nitrox tanks must have a sticker = INCORRECT
- You must test and mark your own tanks = INCORRECT
- What's the point of Nitrox!?!
- Use "Nitrox" on every dive?
- What do you do?
Deeper Discussion
Nitrox allows you to dive deeper
INCORRECT - It's actually MORE dangerous to dive "deeper" on Nitrox than Air. (Oxygen Toxicity)Nitrox allows you to dive longer
INCORRECT - The amount of time you have before you run out of gas is NOT determined by the blend of the gas you use. 80cft of Nitrox is still 80cft of breathable gas. Volume doesn't change. What is actually meant by this statement is that you will have more time before you reach your Nitrox calculated No Decompression Limit (NDL) than if you are using "Air" calculated NDL. However, most recreational divers will run out of gas before they hit their NDL on "air" anyway. So...no...you won't get a longer dive (generally).Above [certain depth] there is no value in diving Nitrox
INCORRECT - "Value" is often assumed to be only a cost analysis instead of looking at the reduced risk. Above the related Maximum Operating Depth (MOD) of the blend you are using, Nitrox ALWAYS lowers the risk of decompression sickness. Only you can determine if an extra $4 is worth the reduced risk...which may be approaching 0...but is never actually 0.Nitrox reduces post dive fatigue
INCORRECT - There are no scientific studies that show anything other anecdotal evidence of this phenomenon. You may feel better sure...that's known as the placebo effect. But don't discount that feeling...maybe that is a valid benefit to you!Common "air" is not Nitrox.
INCORRECT - A mix of 78% nitrogen and 21% oxygen IS Nitrox by definition. It is just not commonly used in that terminology. You can in fact set your computer to Nitrox mode with an EAN21 blend and it work exactly as expected, cause science.Nitrox is always EAN30 or EAN32 or EAN36
INCORRECT - 30% and/or 32% and/or 36% Oxygen is simply a standard mixture that is commonly "banked" by air fill stations. EAN36 (36% O2) use to be more common but 32% has become the standard. You can use any particular blend and call it Nitrox. However, you may have to make a special request to have that blend created, which may or may not be offered by that shop.
All Nitrox tanks must be marked with a Nitrox sticker
INCORRECT - There are no scuba police. The shop that fills your tank can require whatever they want. It's their shop. However, it can be generally said to be a wise decision to analyze and label all tanks regardless of what any sticker might be on it.You must measure the mix yourself and mark it on the tank
INCORRECT - There are no scuba police. There are certainly "best practices" such as measuring or watching the testing of the mix in the tank you will be diving and then physically writing it on the tank, but not everyone follows those "best practices". It is not uncommon on a boat, for example, for a rented Nitrox tank be tested while you watch and then you mark/sign on a log paper instead of on a piece of tape physically on the tank.Well if none of the above is true, what is the point of Nitrox?
For TWO simple reason....and only two.1. Using a gas blend of greater than 21% oxygen reduces the risk of decompression sickness compared to the same dive on "air" (21% oxygen) because it reduces the amount of Nitrogen uptake during your dive.
2. Your surface interval between dives (off gassing) will be shorter because you have less Nitrogen loading because of #1
That's it...there is nothing more.