• What is Nitrox? Advantages and Disadvantages.

    November 1, 2015
  • What is Nitrox, EANx and Enriched Air?

    So exactly what is Nitrox? Simply stated, Nitrox is a mixture of gas that contains both nitrogen and oxygen. In fact, the very air that is in Earth's atmosphere that you are breathing right now while reading this article technically is Nitrox. It contains approximately 79% nitrogen and 21% oxygen. We call it “Air” but when talking about Nitrox the earths atmosphere would be called EAN21. The 21 in “EAN21” represents the fraction (percentage) of Oxygen contained in the Nitrox. See basically, Nitrox can be any percentage mix of nitrogen and oxygen. We call it “Enriched Air” when any mix of nitrogen and oxygen contains an oxygen percentage that is greater than that found in air, in other words any value greater than 21%. Simply stated, the air is “enriched” with oxygen. When you see EANx just remember it is an acronym that is defined as “Enriched Air Nitrox”. The x in EANx represents the fraction (percentage) of Oxygen in the mix. Easy right?

    What are some of the benefits to diving using Nitrox?

    Any diver should know that it is the nitrogen in their breathing gas that tends to cause the most problems. Nitrogen is, of course, known to contribute to Decompression Sickness (“DCS” or the “Bends”). The basic science behind EANx is that by increasing the fraction (percentage) of oxygen in the breathing gas that you lower the fraction (percentage) of nitrogen in the breathing gas and therefore helps to reduce a divers exposure to higher partial pressures of nitrogen. By reducing the amount of nitrogen absorption by diving EANx compared to diving straight “atmospheric air” means longer bottom times by extending the No Decompression Limits (NDL’s.) By reducing nitrogen absorption the benefit is to help limit the risk of developing DCS. This all assumes that the diver practices conservative diving practices such as slow controlled ascents, performing recommended safety stops and of course staying within the limits of their dive computer or the limits of their dive tables.

    Unfortunately among untrained divers the common misconception is that when diving on EANx you will get “more out of your tank”. This is a false belief and is certainly not the case. A 80cf scuba cylinder filled with atmospheric air to 3000 psi has the same VOLUME of gas in it as a 80cf scuba cylinder filled with EAN32 to 3000 psi. The cylinder lasts the same amount of time, however if you are good on your gas consumption during diving, you can experience more bottom time due to less Nitrogen loading. A real bonus to diving with EANx is that as you have less accumulated nitrogen loading in your tissues after diving. What does this mean? You will feel less tired after a day of diving! This is a huge advantage when you are performing multiple dives in a single day over multiple dives over multiple days.

    Does this sound too good to be true? There is always a catch is there not? A common misconception is that diving on EANx is safer that diving on air. The truth of the matter is that it is no safer to dive with EANx than it is diving with straight atmospheric air. Actually using EANx can be less safe if not used properly and without proper training.

    What’s the downside to using Enriched Air Nitrox?

    Oxygen becomes toxic at depth. If you use EANx deeper than the Maximum Operating Depth (“MOD”) then the increased partial pressure of the oxygen in EANx can lead to what is known as CNS Oxygen Toxicity. The symptoms of Oxygen Toxicity may include visual disturbances, nausea, ringing in the ears, dizziness, twitching and irritability. However, the most dangerous and concerning symptom, which can happen without any notice, is for a diver to experience sudden convulsions. It should be fairly obvious that convulsing underwater is highly undesirable and can result in the most severe of diving accidents; drowning and death.

    The more oxygen there is contained in the EANx breathing mix the shallower the Maximum Operating Depth (“MOD”). At the recommended maximum partial pressure of Oxygen (PPO2) of 1.4 atmospheres, the maximum allowable depth for normal atmospheric air (21% Oxygen) would be 187 fsw. However, if you were diving a cylinder that contained EAN36 (36% Oxygen), for example, the maximum operating depth would be reduced to 111 fsw . Careful analysis of your cylinder to determine the EANx percentage that is contained inside is critical to determine your MOD. Following the rules and not exceeding the MOD levels at any time is critical to safe Nitrox diving. This is one of those rules that if you break it could have immediate and severe repercussions.

    So really how much additional bottom time can using EANx really give you? To follow is a practical example. Using atmospheric air on a dive would limit you to an NDL of 20 minutes at 91 fsw. However, by using EAN36 to do the same dive profile would limit you to an NDL of 35 minutes at 91 fsw. Could you use an additional 15 minutes of dive time before hitting your maximum NDL times? Anyone welcomes longer bottom times due to less Nitrogen loading! You just need to always remember although it increases your bottom time, your gas consumption rate remains the same.

    One last thing to note is that over multiple dives your body accumulates oxygen just as it does with nitrogen and the other gases that you breathe. Provided enough time this accumulated oxygen can also become toxic (this is referred to as Pulmonary Oxygen Toxicity). It is therefore very important that you monitor your total oxygen exposure over any given 24 hour period of time. All modern Nitrox capable dive computers will track Oxygen loading for you as long as you program them with the correct percentage value for the blend of EANx that you are using before the start of each dive. In other words, if you are diving EAN32 you need to set the Nitrox value of your dive computer to 32% before you start your dive.

    With proper training EANx advantages clearly outweigh the risks. If you want to feel less tired after diving and possibly extend your bottom times then Nitrox training is probably a perfect fit for you.