Nitrox, voodoo gas or common sense?

In the early 1990’s, nitrox or “voodoo gas” as it was often referred to was the exclusive domain of the expedition or technical diver. Today, with education and aware nitrox has become a common, safe and affordable gas that is considered standard in many parts of the world. Contrary to popular misconception, nitrox doesn’t allow you to go deeper but instead limits your maximum depth limit. What it does do exceptionally well is extend no decompression limits (NDL), meaning you can stay down longer.

Nitrox 101 – the basics

Nitrox or Enriched Air Nitrox (EAN) as PADI calls it basically refers to a oxygen nitrogen blend, where the oxygen percentage is increased. It’s not much different to air, which is roughly made of 21% oxygen and 79% nitrogen. With nitrox, the oxygen percentage is increased, which means nitrogen is removed from the mix. We all know that nitrogen is inert and causes problems for divers, so by removing some of it from the mix and replacing it with oxygen (which out body metabolises) we can stay down longer.

Technically speaking, any oxygen and nitrogen blend is actually nitrox. Considering this, air is actually 21% nitrox. In practice though nitrox always has greater than 21% oxygen and is often encountered in standard mixes of 32% and 36%. The use of standard mixes has been promoted by training agencies such as PADI to make it easier and cheaper to get, as well as standardise decompression tables (largely redundant now with computers). The standard nitrox mixes of 32% and 36% have a generally accepted maximum depth of 34m and 29m respectively (we’ll look at why in a minute). Using the EAN moniker, the actual oxygen percentage is appended to EAN (e.g. 32% is EAN32, 36% is EAN36, etc…

Nitrox is all about extending our NDL so we can stay down longer. Let’s compare using 32% nitrox to air at a depth of 20m:

  • Air NDL @ 25m: 25 minutes
  • EAN32 @ 25m:  43 minutes

Using this simple example, you should be able to clearly see that you get a longer dive on nitrox. At 25m, most experienced divers will have lots of air left after 25 minutes but yet will be forced to end the dive due to no decompression limits. Using nitrox, you’d get to stay on that wreck or reef 18 minutes longer. Nitrox really comes into its own when you’re talking about repetitive diving. Basically because you’re inspiring less nitrogen, surface intervals can be dramatically shortened and repetitive NDL are seriously extended.

Things to consider

Training – nitrox training is dead easy. The good news is you already know 90% of what you need to in order to dive (you learnt this in you open water course). The basic nitrox course lets you use nitrox with oxygen up to 40% and will cover you for all the recreational uses that nitrox offers. Training today doesn’t even require that you get into the water and does not force you to use tables (you can use your nitrox computer).

Cost – nitrox does cost more than air. At SGU, a 32% fill will cost $[XX] compared to $[XX] for air. The financial question is whether increased bottom time is worth $[XX]. For a sure dive, this makes no sense. On a boat dives however, where you dive at increased depths and the time on the bottom is what counts, suddenly your $[XX] makes a lot of sense.

Equipment – standard regulators can be used with nitrox up to 40%. The bad news is that depending on how you make nitrox, your cylinder will need to be oxygen clean and labelled for such use (e.g. with the green/gold band). This is because pure oxygen is put into the tank during the partial pressure blending process. There are others ways to make nitrox that don’t need clean, but unfortunately they’re not yet available at SGU. Oxygen clean cylinders are available free of charge for club members (subject to availability) if purchasing a nitrox fill from SGU. You will also want to be using a nitrox computer to get NDL benefits – but all modern computers support nitrox.

Technical Diving

Now we said earlier that nitrox used to be the exclusive domain of the technical divers, but then said that it limits your maximum depth. Both are true, but the use case for nitrox in technical diving applications is slightly different. The primary purpose for nitrox on technical dives is to accelerate decompression, which is typically done using one or more nitrox mixes with high oxygen content (typically > 50%). Using nitrox in this capacity gets a little more complex and this type of usage is covered in advanced nitrox and decompression courses for dives to depths greater than 40m.

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