In the world of recreational diving, brightly tagged green and yellow tanks mark the presence of oxygen-enriched air, commonly known as nitrox. Scuba divers typically use nitrox air in their tanks if they want to spend more time underwater. But what exactly is nitrox and how does it help you while you’re diving?
Identifying Nitrox Tanks
For recreational diving, enriched air nitrox (EAN) refers to any nitrogen/oxygen gas mixture with an oxygen concentration higher than the 21 percent present in normal air. Most commonly, nitrox tanks are available at a 32 percent oxygen concentration. EAN tanks are usually marked with a nitrox band and listing the percentage somewhere near the tank valve.
What’s the Advantage?
When diving with nitrox, divers can lengthen the no-decompression limits, shorten surface intervals and have that added buffer of safety for decompression sickness (in certain circumstances) by using this higher percentage of oxygen with proportionately lower percentage of nitrogen.
How Nitrox Works
As divers learn through certification, when diving, water pressure causes nitrogen that is breathed in to dissolve into the bloodstream. The higher the pressure, the more nitrogen dissolves. With a certain concentration of nitrogen build up, divers must slowly return to the surface to avoid mandatory decompression stops and before decompression sickness (DSC) can occur.
Based on the U.S. Navy dive tables, a diver at 100 feet using air will reach his or her decompression limit and will need to come back up to surface after 25 minutes.
Nitrox works a bit differently, using a concept known as the equivalent air depth (EAD) formula. Replacing some of the nitrogen with extra oxygen will make less nitrogen available to bloodstream and therefore will allow a longer no-decompression limit. Here’s an example. Diving at 105 feet with 36 percent nitrox will dissolve nitrogen into the bloodstream and tissues at the same rate as if breathing air at 80 feet. This means that the diver’s ordinary no-decompression limit of 20 minutes can be prolonged to 40 minutes – two times the bottom time.
Risks of Diving with Nitrox
Before learning how to dive with nitrox, one should understand potential risks. Oxygen, although essential to life, can become toxic and hazardous in high concentrations. If not managed properly, acute oxygen toxicity can result, with potential side effects ranging from visual distortions, or convulsions that can lead to drowning.
Any percentage of oxygen can cause toxicity at a high enough pressure. However, a diver using regular air would have to exceed 220 feet to experience of acute oxygen toxicity. However, nitrox brings more possibility of danger within recreational diving depths. This is because of two factors. One is the amount of exposure, or the pressure of oxygen in the lungs. The other is the length of the exposure. These two factors together are called the oxygen limit.
Divers desiring to use nitrox should obtain appropriate training and certification, and be adept at calculating the pressure component of the oxygen limit for their dive. To stay within the safe depth limitations of their mix, nitrox divers use a table or complete a maximum operating depth (MOD) formula before each dive.
Benefits of diving with nitrox
There is a misconception that you can dive deeper, but actually it is just the opposite, but you can dive for longer. The 50- to 100-foot range is the best application of nitrox because of the no-decompression times for dives shallower than 50 feet extends the time period so long that most divers will use their entire tank before they ever run out of dive time. With this deeper depth range, bottom time diving can be doubled with nitrox under the right circumstances.
If a diver has any risk factors for decompression sickness, precious DCS hits, physical injuries or older age, choosing nitrox and its corresponding air table can add significant security to their no-decompression limit zone. For example, divers breathing EAN 36 could do a dive to 60 feet for the maximum limit of the U.S. Navy air table and still be more than 60 minutes from reaching their no-decompression limit. While there is no 100 percent guarantee of safety, logically, the further you are from the no-decompression limit, the less likely you are to get bent.
The PADI Enriched Air course will help you understand the relationship between pressures, gas absorption and why limits are important. If you’re looking to take your diving to the next level, Divemaster or above, then this understanding will assist you in explaining to less experienced divers the details of dive planning.