Getting technical

The Basics
Nitrogen makes up 79% of the air that we breathe, with oxygen making up the other 21%. Our bodies don’t use nitrogen, but underwater and under-pressure, our bodies absorb it. When we ascend towards the surface and the water pressure reduces, our bodies begin to release it.
The deeper you dive and the longer you spend underwater, the more nitrogen your body absorbs... and the more it needs to release before you end your dive. Learning to safely manage the relationship between your body, the gases you breath and the effect the surrounding water pressure has on these elements is key to all technical diving.

All recreational divers understand concepts such as decompression limits, nitrogen narcosis and the effect of increased pressure on our bodies and the air we breathe. Technical divers are trained to intimately understand these relationships and learn to plan dives to take account of every eventuality.

As a diver, you know that if the nitrogen load is too much or if safe-ascent procedures are violated then this can cause nitrogen bubbles to form in the body. These bubbles can cause decompression sickness, otherwise known as ‘the bends’.  In recreational diving you are trained to stay within limits that restrict your absorption and allow your body to ‘off-gas’ this nitrogen whilst slowly ascending to the surface.  At 40 metres, as a recreational diver, your limit is just 9 minutes. As a technical diver, you learn how to extend these limits and increase your bottom time while still staying safe.
Deeper water and increased pressure also squashes the air in your tank, meaning that the deeper you dive the more air you will use.  At 40 metres you will use your air 5 times as fast as you would on the surface. This is a problem if you are not prepared and have a lot of nitrogen to release. Technical divers carry more than one tank in order to mitigate this risk and minimise the likelihood of running out of air.

Nitrogen dissolved in your tissues also causes a narcotic effect similar to that of alcohol, usually referred to as ‘being narc’d’.  Whilst not physiologically dangerous, losing your mental reasoning underwater can cause the diver to make mistakes. At 40m you can feel like you have consumed a few beers, making it even more important to have a very clear dive plan and an intimate understanding of both your body and surrounding environment - things that will begin to become second nature as you progress as a technical diver.

Beyond The Limits
Dive beyond the no decompression limits and you must stop on the way to the surface to allow the excess nitrogen that you have absorbed to safely leave your system. Sounds simple enough, but just having the requirement to stop on your ascent means you no longer have direct access to the surface – you have a very real ceiling above your head which cannot be breached without risking injury.

While your decompression schedule can be completed breathing air, most technical divers prefer to use nitrox blends while decompressing, as the higher oxygen content speeds the bodies release of nitrogen. Technical divers plan their ascents in great detail, calculating not only where and how long the decompression stops are, but also when to breath which gas - and how much of each gas is needed.

As you cannot ascend directly to the surface without risking injury, you must have all the equipment necessary to enable you to deal with failures or emergencies underwater - and know exactly how to use it. Think about it.... if your mask strap breaks, then you can’t read your dive plan, gauges or computers. So how will you complete your decompression schedule? Training as a technical diver equips you with all the knowledge and safety procedures necessary to deal with scenerios such as this calmly and safely.

The Helium Effect
So if the oxygen in air becomes toxic at 66m, to dive deeper you must reduce the amount of oxygen in your gas. Replacing it with nitrogen is not possible due to it's narcotic effect, plus higher nitrogen content will increase decompression obligations - meaning it will take longer to safely return to the surface. This is where helium comes in.

Helium is an excellent gas to fill this void. It is an inert gas, meaning it will not react with the other gases in your tank, or with the gases inside your body. And as it is non-narcotic, it will actually reduce the narcosis effect, allowing you to think more clearly and precisely at depth. By utilising helium, technical divers are able to succesfully extend the depths to which they can dive and explore.

To go really deep - say around 90m - you will need to reduce your oxygen content to around 15%, yet our bodies need a minimum of 18% oxygen to maintain consciousness. When we are underwater however, the increased pressue means that a mix with just 15% oxygen will be sufficient to sustain consciousness at any depth below 5 metres. Simply by breathing from helium below this level and nitrox above, will overcome this problem.