diving-computer. So why not breathe an air that has less inert nitrogen gas and so reduce the problem? If you’ve been breathing air, you’ve already been breathing nitrox – nitrox21. Other nitrox mixes have the percentage of oxygen increased and therefore the percentage of nitrogen is decreased. Nitrox 32 has 32% oxygen and nitrox36 has 36% oxygen. Breathing a richer nitrox mix instead of plain old air reduces the chance of decompression illness due to a diver staying down too long or coming up too quickly - providing no-stop times and ascent-rates for air are adhered to. If you want to continue with conventional levels of caution you can simply adjust your decompression requirement by adjusting your computer to match the nitrox mix you use and in that way get more time underwater. However oxygen too has its problems too. Pure oxygen becomes poisonous at quite low pressures. It is currently thought unsafe to breathe pure oxygen at a greater pressure than 1.6 bars underwater and that occurs at only 6m deep. Therefore each specific nitrox mix has its own maximum operating depth and nitrox training agencies are unanimous in limiting the use of oxygen to 1.4bars of partial pressure within a mix with nitrogen. What you need to know is that the oxygen in air (nitrox21) can become hazardous at 54m deep. That does not affect leisure divers limited to an absolute maximum depth of 40m. A standard mix of nitrox32 should not be breathed deeper than 32m. Some training agencies tells new divers that this limit is 30m. Most popular sites for diving in the world now adhere to a 30m limit for leisure diving anyway. PADI Open Water Divers with Level One training are still limited to a maximum depth of 18m during training as before but suitably qualified divers can use nitrox32 to its full maximum operating depth (MOD). So for nitrox mixes up to 40% oxygen, no additional diving equipment is needed, only the knowledge of how to analyse the contents of a tank before diving, using the analyser supplied by the dive-centre and knowing how to set your computer to match. The day is foreseen when all new divers will start off breathing nitrox and air for diving will only be for specialised uses. More advanced divers that have been deeper than normal leisure diving depths use nitrox to speed up their decompression. They take additional tanks of rich nitrox with them and swap to these once they have ascended shallow enough for it to be safe do so. There are more advanced diving computers that allow you to set different levels of nitrox and to switch to the one that matches the actual mix the diver is currently breathing, and in that way track both decompression requirements and oxygen exposure accurately. All the diving computers sold at Ocean Leisure are nitrox compatible. If you want to know how to take high-speed sequences of pictures or successfully take photographs underwater, ask the guys at Ocean Leisure Cameras.What is Nitrox? Air is mainly made up of two gases – 21% oxygen and 78% nitrogen (1% other gases). We metabolise some oxygen in the air we breathe but the greater part, the nitrogen, is inert. When we put ourselves under pressure, as we do when we go under water, our bodies absorb some of this inert nitrogen. As we go deeper and stay longer we absorb more. The time that we spend underwater is limited by the amount of that nitrogen we absorb. That is why we used to use tables or, more recently, a
Scuba diving should be in no way competitive. If you are part of a group of divers, you want everyone to have a good time. That said, the human spirit is without doubt naturally competitive and we will find ways to compete, however irrelevant. You’ll often see divers post-dive comparing how much air they used. Somehow it’s often seen as clever to use less than the next person. I was on a dive trip once where my buddy used exactly half the gas I went through. Did this mean he was a better diver? Another friend of mine was supremely fit. When his family came to visit, his wife and daughter would drive over from their home ten miles away but he would always prefer to run. The London Marathon? He completed runs across the Sahara! However, when we went of a dive trip together I was amazed at the rate of knots with which he went through his air supply. I put it down to poor technique at the time. Then I went away diving with a young television Gladiator, Hunter.He was young and fit and made me look totally puny by comparison. It was lucky he could easily manhandle an 18-litre cylinder because that is what we had to get for him to allow him any time underwater on the shallowest and most benign of dives. On the other hand, Umberto Pelizzari, formerly the free-diving world champion, uses yoga to reduce his breathing requirements to negligible levels. One quickly comes to realize that women generally use less air than men on dives. Is it because they are serene and become part of the underwater environment unlike men who tend to be more active? Or is it because they are usually smaller than men and thus have smaller lung capacities? I’ve dived with elderly over-weight ladies who went through less air than me, and a lot of other people, so it’s probably a combination of both. Recently, I was diving with twin-cylinders on a deep dive in Truk Lagoon. A rather large lady of a certain age did the dives with a single 11-litre cylinder of air while her very muscular husband went in with her, armed with twin-cylinders (like me) plus an additional side-slung tank. The dives required considerable decompression stops. I asked if he carried the sling-tank for his lady wife but was told she didn’t need it. He did! What about my lightly breathing friend? Well, he could come back with half a tank of air when I was completely out but he couldn’t get through the night without waking up for a cigarette. He was a very heavy smoker. He also ended every dive with a humdinger of a headache. Am I saying that divers should take up smoking? Definitely not! New Zealander, Professor Simon Mitchell has investigated a subject that could be connected with the smoking phenomenon. He has studied carbon-dioxide retention in divers. Some people are able to retain a lot more carbon dioxide during the act of breathing than others and as you may know, it is the build-up of carbon dioxide that triggers our breathing reflex. It’s not the lack of oxygen but the raised levels of carbon dioxide that makes us have the desire to breathe. As I understand it, carbon-dioxide retainers breathe less. As a complete non-scientist, I wonder if heavy smokers with their constant lung exposure to carbon monoxide get a raised tolerance to carbon dioxide too, so that they can skip-breathe, leaving longer intervals between inhalations. Maybe their lung volumes have simply become very small due to the build-up of tar. Whatever the reason I’ve noticed they are more economic with their air supplies underwater. Cyclist Bradley Wiggins is supremely fit. After winning the exhausting 2172-mile Tour de France, a few weeks later he was competing in the London Olympics road race. How’s that for stamina? I read on the BBC website that he probably has huge left ventricles to his heart, which allows more oxygen-rich blood to be pumped to his muscles than we more ordinary folk. Chris Boardman, the Olympic Gold medalist in the Pursuit at the Barcelona Olympics in 1992, with whom I once dived a lot, had a resting heart-rate at his peak of around 38 bpm which indicates a large heart. I noticed he was an experienced diver who was able to be very relaxed on dives, with good technique and perfect neutral buoyancy, so that he didn’t rush through his air. A person’s endurance can be measured by taking a reading, which indicates how much oxygen is used every minute for each kilogram of body weight. It’s called a VO2 Max reading. A typical young male might have a VO2 Max of around 40 whereas a top cyclist might have a value of twice that, so that not only are they able to use more oxygen, they can also keep their muscles active for longer periods of time. Of course, cyclists have a never-ending air supply whereas for a diver it’s totally finite. I suggest it’s not clever to use less air than anyone else on a dive, although it may under certain circumstances be fortunate. I suggest it’s more intelligent to take sufficient gas with you for the dive in question and to manage that supply in such as way that you get back safely. Unlike running races and competitive cycling, it’s not a competition. A gas-integrated diving computer will help you manage your air supplies.