Reasons to get Nitroxicated
By Phillip Christoff
Nitrox was the first specialty course I took after my Open Water and it did not come about the way you usually sign up for a specialty. A few weeks after completing the Open Water course, while visiting relatives in Florida, my certification finally came in the mail and to my surprise the card read ‘Enriched Air Open Water Diver’. As most divers who enrol in an Open Water course, I began my diving breathing dry compressed air. Nitrox or Enriched Air Nitrox refers to diving with breathing mixtures containing a higher percentages of oxygen.
Sat at the dinner table with my family I was very happy to have been given this additional ‘free’ certification. My father was sceptical and asked me to explain what Nitrox was. As I stumbled my way through a rather poor explanation my grandmother chimed in “Philip, you are going back to that shop tomorrow and signing up for that course!” I knew that tone and two days later I had completed my Enriched Air Nitrox course. A year later in Thailand I signed up for my advanced course and used Nitrox for three of the five dives. I enjoyed the longer bottom time exploring the outside of my first wreck and looking for leopard sharks on the local reefs. At this point I was fully nitroxicated and later when I started my Dive Master in Indonesia I took every opportunity I had to dive Nitrox.
When I finished my Dive Master course I started exploring the outer deeper edges of our reefs using Nitrox as the main tool to allow enough bottom time for mapping and searching. As I approached the limits of recreational Nitrox I started looking for other options to push the exploration. That is what lead me to technical diving and a whole new level of adventure. Looking back it all started with a minor printing mistake, good advice from my dear family and a solid Nitrox course. In this wetnote I will give you some of the background of Nitrox, the main advantages and dispel some common misconceptions.
Prior to 1970, Nitrox (as with many innovations in the diving world), was used almost exclusively in commercial and military diving. During the 70’s, scientific divers working for the US National Oceanic and Atmospheric Administration (NOAA) began using Nitrox for scientific dives. In 1978 the first Nitrox diving procedures and tables were published by NOAA. Two standard mixes were used; 32% O2 and 36% O2. Initially Nitrox was not embraced by the diving community as concerns were raised regarding the safety of using higher oxygen mixes and heated discussions followed. Many agencies were sceptical and initially new agencies were formed to meet the demand for Nitrox such as the International Association of Nitrox Divers (IAND now IANTD) as well as American Nitrox Divers Inc (ANDI) which are still around to this day. As more and more divers became interested in Nitrox over the 90’s the controversy settled and Nitrox slowly became accepted into the mainstream diving community.
Today, Nitrox is one of the most popular specialties within diving offered by agencies and dive shops. It’s hard to miss the yellow and green tank labels that are becoming increasingly visible on dive boats around the globe. Equipment manufacturers now make programmable dive computers allowing divers to easily program in their Nitrox mix and specific Nitrox regulators are being produced for mixes with higher oxygen content. Divers are using Nitrox to get more time under water for everything from reef clean ups to underwater photography.
Benefits & limitations
As you may know, the amount of time a diver can stay submerged depends on several factors but two of the main limitations are quantity of gas and nitrogen absorbed. As divers breathe under pressure, nitrogen is absorbed into the bodies tissues. The deeper the diver goes the faster this absorption takes place. In no-decompression or no-stop diving we have tables indicating the amount of time a diver can spend at a given depth without the need to stop on the way back to the surface, these tables are the basis for dive computers that calculate in real time how long a diver may stay submerged.
By increasing the oxygen content and thus reducing the nitrogen content in the breathing mixture, a diver can stay longer at a given depth. However too much oxygen can cause problems such as Central Nervous System Oxygen Toxicity and Pulmonary Oxygen Toxicity. Thus every Nitrox mixture has a maximum operating depth and a diver must track their oxygen exposure over time. As this blog post is not intended as training tool you will need to enrol in a Nitrox course to learn how to use Nitrox safely; there is no replacement for good training.
1. Longer bottom times
As Nitrox reduces the nitrogen exposure of a diver, the diver may enjoy longer times at a given depth while remaining within their no-decompression limits. For example, a dive to 30m using air will allow for a bottom time of 17 minutes while the same dive using a Nitrox 32% oxygen will allow for 27 minutes of bottom time*. For me this was always my advantage of choice, especially as I started getting into underwater photography. More bottom time meant more time to find sharks rays and all the other amazing marine life to photograph.
2. Shorter surface intervals
When divers surface after a dive they have remaining nitrogen in their system. Divers will wait on the surface until the nitrogen levels have dropped before going on a second dive. As a Nitrox diver will have absorbed less nitrogen than a diver doing the same bottom time on air they can wait for a shorter time on the surface before going on their next dive. This is great for live aboard diving where a diver can often make 4-5 dives in a day.
3. Lower nitrogen exposure
Some divers choose to use Nitrox but still follow bottom times for air. This is done to reduce the nitrogen exposure and decrease the risk of Decompression Sickness. Thus this could be viewed as a more conservative way to dive provided the diver adheres to the depth limits of the Nitrox mix.
Note that divers must choose one of the advantages in planning their Nitrox dives as they all have an effect on each other and the advantage will diminish if combined.
1. Nitrox allows divers to dive deeper
As dives in the 25-40m range become limited by bottom time, divers often opt for Nitrox when diving to these depths. Unfortunately some people see this and assume the Nitrox allows them to dive deeper. The Nitrox actually limits their depth but allows for more time.
2. Divers on Nitrox experience less narcosis
This claim sounds credible if you assume only nitrogen is narcotic however we know that oxygen may also contribute to narcosis so overall, Nitrox has not shown to lower the effects of narcosis.
3. You use less gas when diving Nitrox
The oxygen content in a breathing mix will not have an effect on how quickly you consume the gas in your tank and thus you will see no difference when diving Nitrox.
In decompression diving where divers plan dives where they stop at predetermined depths to “off-gas” before returning to the surface, Nitrox is used to shorten decompression stops. By breathing a high oxygen mix in shallow water, a technical diver can much more efficiently release the nitrogen they have absorbed, shortening their decompression. As an example, a diver who wanted to do a 30 minute bottom time at 45m on air will have to do 68 minutes of decompression if staying on air but only 36 minutes of decompression if switching to an 80% Nitrox mix at 9m.*
So if you are looking for longer bottom times, shorter surface intervals or lower nitrogen exposure, as a recreational diver it may be time to have a look at enrolling in a Nitrox course and seeing what it’s all about!
*All dives planned using Shearwater Petrel 2 gradient factors 45/85. Last stop 3m.
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Photo credits: Alfred Minnaar