eDiveSoftware blogs

Firstly, this is a more general and laymen's outline on how to scuba dive as a beginner on Nitrox. I'll be writing again soon with a more technical outline on Nitrox Dive Planning showing detailed examples of some of the areas outlined below. For now, enjoy.

Most divers these days already have an idea of what Nitrox is. It's plastered pretty much everywhere. The majority of dive schools either have it or have access to it. Most diving fraternities also advocate its use as being 'safer'. But for those that have only just come across diving and about to take the plunge, what exactly is this Nitrox stuff ?

Nitrox is not a deep diving gas - it's used by sports divers as well as technical divers so don't fall into the trap that is 'off limits' to those preferring to do deep dives. Okay, so Nitrox, taken element by element, is pretty much what is says on the can - Nitrogen and Oxygen. Taking away the almost insignificant base elements in the air about us we breathe every day, air is made up of 21% Oxygen and 79% Nitrogen. That compressed gas in you diving cylinder is pretty much exactly that.

So what's all the fuss about then? Surely we are all breathing Nitrox already. Technically speaking yes but in diving terms the gas 'air' that we breathe is 'standard' and as such not referred to as Nitrox. Once you change that composition however, then you start getting into the realms of Nitrox mixes and diving. The Nitrox divers are interested in are mainly those that contain a larger than normal percentage of Oxygen (i.e. Hyperoxic) - air that has been 'enriched' hence the terms 'enriched air' or EANx (Enriched Air Nitrox).

For example, say we push the amount of Oxygen up to 30% we'd reduce the amount of Nitrogen down to 70%. But why do that? Well, you need to understand what, in theory at least, is physically going on in your body once submerged. We'll take a simple example at ten meters depth in fresh water. I'm simplifying this as not taking the weight of water to be exact etc. - that's another blog!!! Anyway, at ten meters, the pressure of the body of water above you exerts double that of the surface (aka 2 atmospheres or 2 atm). For each breath we take our body 'absorbs' double the percentage of both Oxygen and Nitrogen for that depth i.e. 60% Oxygen and 140% Nitrogen...Hey, what you might ask? How can you absorb 140% Nitrogen (Standard air, in comparison, is almost 160%)? Well, its physics plus the biological processes involved. Again, without getting into the complexities and keeping it simple, just take my word for it. What this basically means is that, at ten meters, your body is absorbing a fair portion of Nitrogen (double that of being on the surface). This Nitrogen, under pressure, is held in 'solution' i.e. its 'floating' around in every orifice in your body waiting for the pressure to be released so it can be turned back into a gas and released from your body. It is during this process that divers succumb to what is often referred to as 'the bends' (blockages in joints, fluid bays etc. as this gas has expanded causing untold pain and misery to put it nicely).

To put it in really simple terms, the more Nitrogen you absorb, the more you have to release. So, in theory at least, the less Nitrogen you absorb in the first place, the less you have to release. So, it must be safer then? Well, that depends on how you look at it. Taking less Nitrogen on board certainly, by diving standards, is accepted as putting you and your body in a better position. However, as is with everything in life, every action has an equal and opposite.

The problem with removing the Nitrogen is that you have to increase the other gasses.

Without getting into 'Trimix' and sticking with just Nitrogen and Oxygen, you end up with a lot more Oxygen. Well, that's great isn't it? The problem again relates to biology. The human body has a very finite line between what is acceptable in terms of the amount of Oxygen you can breathe. Too much and it becomes toxic. This is often termed as 'Oxygen Toxicity' of which there are two types, namely Central Nervous System (CNS) and pulmonary toxicity. CNS is usually caused by short term high exposure resulting in convulsions (which invariably end up in the diver drowning). Pulmonary toxicity is lower exposure over long durations.

So what does all this mean in laymen's terms? Well, you have to account for the depth you are diving too, to ensure that you firstly do not exceed the human body's tolerance to high levels of Oxygen - the 'partial pressure' of Oxygen (aka 'PO2'). You also have to take into account the duration and all subsequent durations of oxygen intake to ensure that you do not exceed industry standard.

That aside, what are the real risks? As already mentioned above you don't want to exceed the body's limited to the partial pressure of the Oxygen you are breathing. This is mainly down to the depth you will dive at - thus you will have a very firm maximum operating depth (aka 'MOD'). With normal air you generally (at sport diving depths) result in light headedness, feeling dizzy etc. (aka 'narcosis') which can also have obvious side effects. With Nitrox the risk of Oxygen Toxicity is much higher and unfortunately there is little or no warning of an attack. That said proper dive planning using standard Nitrox tables certainly helps to reduce that to a minimum.

Other factors which should be taken into account are those such as the 'average body'. Who has an 'average body'? Well, no one really. What we are getting at here is that on one day at a certain depth all may be well. Next day, same depth and you could be in for real problems. Add a degree of a 'safety margin' and don't push you luck. Most diving tables have a degree built in for a very good reason. Keep to the guidelines and keep your maximum partial pressure for the Nitrox you are breathing at a safe level. You will also need equipment that has been oxygen cleaned for nitrox so check with your club about which kit you need. Most major manufacturers such as Mares, Poseidon and Faber etc...all cater for nitrox

There are also training and equipment plus 'Oxygen Handling' requirements plus other issues but for now we can put those to bed for another blog.

Well, that's all nice and dandy. We know what Nitrox is, we know the risks and all sounds gloomy. But wait...there are some very nice benefits!!!!

Making the very large assumption that all and I say again ALL, the guidelines are followed then the benefits for diving on Nitrox mixes far outweigh diving on normal air. Firstly you generally end up with a longer no decompression limit (aka 'NDL') which means longer bottom time!! You can dive for longer assuming that everyone else is diving on the same mix too. Due to the less Nitrogen being absorbed by you will inadvertently end up with a reduced decompression penalty. For sports diving this would generally be realised once back on surfacing. Due to the increased partial pressure of the Oxygen when slowly returning to the surface there is a natural tendency of off gas the Nitrogen much quicker reducing the length of any decompression obligations. Furthermore you have a shorter surface interval (that time 'off gassing' prior to your next dive) due to a lower residual nitrogen in your system. Many divers have also noted that, probably due to the reduced levels of Nitrogen in the system but may also be due to the higher levels of Oxygen, they feel less lethargic during surface intervals.

So...is diving on Nitrox safer? That's really open to debate. My view as is shared by many divers is this. Taking into account and following all the industry standard practices and guidelines I get a longer dive, my body is subjected to much less stress (both physical and mental), I feel on top of the world both during dives and surface intervals and I personally feel it's 'safer'. Clarifying exactly what you term as 'safe' is another thing.

It may also be interesting to note that, since switching to Nitrox, I have very rarely dived on anything else. There are also rumours abound, and it must be said these are rumours, that Nitrox will become the standard for sports diving. That being the case then surely there must be something in this stuff we call 'Nitrox'.

Gaz - One of the founders of eDiveSoftware Ltd