Nitrox Courses
Nitrox Diver is the entry level course for divers who want to expand their theoretical and practical skills, and wishes to learn about the benefits of diving with oxygen enriched air. The course contains theory and practical diving , focusing on safe use of nitrox for no decompression dives with a maximum of 40 % oxygen, and a max depth of 40m.
Decompression Nitrox Diver (Advanced Nitrox / Tec 1) course builds on the basic theory from the nitrox diver course, but includes more training and theory on the benefits of nitrox for use as a decompression gas. On this course you will learn to safely use nitrox mixes for carrying out decompression on dives. (This can be done using single cylinder with pony or full tech setup of twinset and side-mount with 75% - 100% oxygen).
Information for Nitrox Dive and Diver
What is nitrox ?
In diving terminology; any mixture of nitrogen and oxygen, where these two gases represent the major constituents of the gas mix, is termed nitrox. Note that mixes which contain more than trace levels of other gases in addition to nitrogen and oxygen are not nitrox. Air is considered a nitrox mix. Nitrox mixes which are hyperoxic (contain more than 21% oxygen) are variously known as; enriched air, enriched air nitrox (EAN or EANx) or SafeAir. For the most part, sport divers will only be interested in hyperoxic nitrox mixes.
Nitrox ? EANx ? Enriched air ?
Everyone of us has breathed nitrox. Nitrox means a mix of nitrogen and oxygen and the word "nitrox" doesn't tell the relations of those elements. So air is nitrox too because it contains (basically) nitrogen (79%) and oxygen (21%). The base of word nitrox is the expression Nx/Ox, where N is the chemical sign of nitrogen and O is the chemical sign of oxygen. So basically nitrox can be any mix of nitrogen and oxygen containing 1 to 99 % of oxygen (and rest is nitrogen).
Enriched air oxygen means a nitrox mix which has more oxygen than air has, so then the mix has 22-99% of oxygen. Enriched air nitrox has also shorter name, EANx, where x is the percentage of oxygen, ie. EAN40 (40% oxygen in the mix). Also EANx40 label is used sometimes (the letter "x" is preserved in the label). Usually people mean EANx when they say "nitrox", and so do I further here.
However, it is important to the relations of enriched air nitrox and nitrox, because nitrox can also be "hypoxic" mixture containg less oxygen than air !
Then we say that the mix is hypoxic, ie. it has less oxygen than 21%. Hyperoxic nitrox is EANx, and normoxic nitrox is basically air, 21% of oxygen and 79% of nitrogen. Hypoxic mixtures are not recreational diving, but air and EANx usually are.
History of nitrox diving
In about the year 1890 scientics discovered to benefits of enriched air in diving in theory. The first real mass diving tests were conducted during the World War I and a little before. During the WW II it was used much more, and the first open circuit EANx equipment were used.
In the year 1979 USA's National Underwater and Athmospheric Administration (NOAA) published EANx diving tables.
International Association of Nitrox and Technical Divers ( IANTD and PDA - Tec ) bas established in the year 1985 (USA) and IANTD UK in 1992 (Europe). ANDI and TDI were also quickly in markets.
In 1995 PADI (Professional Association of Diving Instructors) took nitrox training as a part of it's training program, and the course certifies diver to dive nitrox dives within the recreational limits and with blends of 22%-40% of oxygen.
Myths.jpg)
Besides the safety myth above, there are several myths regarding nitrox diving : People who don't know much about nitrox think sometimes that it is used for deeper dives. Well, it is not, but it is mostly used on mid deep dives, ranging from 60 -130 fsw. The more oxygen you have in the mix, the shallower will the MOD ( maximum operating depth ) be.
Is air nitrox ?
Yes. Air is, roughly, a mixture containing: 78.05% nitrogen + 20.95% oxygen + 1% trace gases including; carbon dioxide, carbon monoxide and various inert gases - mainly argon.
What is equivalent air depth with nitrox EAN x ?
The ability to equate the actual depth to an equivalent air depth is one of the fundamental principles underlying nitrox diving. One of the limitations in scuba diving is the inert gas we absorb while underwater. It governs our decompression obligation. By reducing the fraction of inert gas in our breathing mix we reduce the partial pressure we experience of that gas at any depth when compared to air at that same depth. Since the absorption of the inert gas is controlled by the difference between the partial pressure in our tissues and the ambient partial pressure it follows that we will absorb less inert gas than we would on air at the same depth over the same period of time. Thus the equivalent air depth is the depth on air at which we would experience the same nitrogen partial pressure, absorb the same amount of nitrogen and incur the same decompression penalty for our actual depth on nitrox.
The equivalent air depth (EAD) is calculated using the formula:
EAD = ( FN2 * (d + x) ) - x
0.79
Another Form of the equation can be shown as :
EAD = FN2 * (d + x) - x
0.79
Where:
* FN2 is the fraction of nitrogen in the nitrox mix
* 0.79 is the fraction of nitrogen in air (including the trace gases)
* d is the actual depth in the appropriate units (fsw or msw)
* x is the depth of water equivalent to 1 Bar in the appropriate units (33 fsw or 10 msw)
Using an EAD enables dives on nitrox to be planned using standard air tables. When diving on air the EAD is the actual depth. On a hypoxic mix (<21% O2) the EAD would be deeper than the actual depth. On a hyperoxic mix (>21% O2) the EAD will be shallower than the actual depth.
This is how nitrox dive profiles are calculated. For a given nitrox mix and a planned maximum actual depth (or partial pressure) the dive is planned using the EAD to get a bottom time and decompression obligation. The EAD is also used to calculate surface intervals and repetitive dive penalties. Tables are available for nitrox I and nitrox II which have already taken the EAD information into account. It is not difficult to generate a nitrox table for a different mix with either custom or commercially available software
Why would you want to use nitrox ?
In short, the correct nitrox mix can be safer than air for the diver. However, we need to qualify that; by correct I mean the most appropriate mix for your dive and it's safer provided you follow the guidelines for its use. There are some additional guidelines to follow (when compared to air) and some priorities have changed. Some of the benefits are listed below, for hyperoxic mixes (i.e. EANx), but it should be noted that some of these are a double edged sword and could also be disadvantages if the guidelines are not followed.
* Longer NDL. Because we work to an EAD the NDL for our actual depth on nitrox is the one which applies to our EAD. This will be shallower than our actual depth, thus the NDL will be longer than if we were using air
* Reduced decompression penalty due to the lower level of nitrogen absorbed during the dive. This may be realised by surfacing according to the nitrox tables or as an additional safety factor by following the standard air tables.
* Shorter surface intervals and longer subsequent dives due to the lower residual nitrogen level following a dive. The surface interval is followed for the EAD not the actual depth. Again it may be used as safety padding by following the standard air surface interval.
* Nitrox provides faster off-gassing than air during decompression. It may be used to reduce the length of the decompression penalty by following a nitrox decompression schedule, or it may be used as padding to increase the safety factor by following an air decompression schedule. This is similar to the use of pure oxygen during decompression. On the surface it also provides an alternative to pure O2 in situations where it is desirable to breath a mix with a higher O2 percentage than air.
* The reduced level of nitrogen in your system has also been claimed to reduce the feeling of lethargy or tiredness following a dive, this is thought to be due to a reduction in sub clinical DCS ie a reduction in the number of asymptomatic bubbles in our system after a dive.
The following claims are also made of nitrox
* Lower gas consumption due to the higher percentage of oxygen in the mix.
* The effects of a barotrauma may be reduced. This is supposition based on improved circulation due to high blood oxygenation and lower nitrogen level implying fewer nitrogen bubbles.
I have also heard the shallower maximum depth proposed as a benefit. The basis being that having a shallower maximum depth means you are nearer the surface in case of emergency (for no stop dives). However, I would assume that you dive to the depth that you planned and that the breathing mixture is appropriate for that depth. If you follow the guidelines, the maximum depth is largely irrelevant because you have factored that into your dive plan. If you do happen to be in situation where the mix in your cylinder is not what you hoped for the you should either change your dive plan or not dive at all. Pushing the oxygen toxicity limits of nitrox is as risky as pushing the oxygen toxicity limits of air - you may not come back from the dive.