I used to take photographs under water with the aid of a snorkel. Helpful friends suggested that I use an aqualung, but at that time scuba-diving seemed far too complicated. Breath-hold diving was simple.

Times have changed, and now half the people you meet seem to be learning to scuba dive. Though only a minority would claim to be technical divers, many others might be surprised to learn that, under some definitions, they are already.
So what is a technical diver

The term was coined in the USA to differentiate between the great majority of people who learned to dive on holiday - taking on board basic information on a need-to-know basis - and those who extended their experience beyond that allowed under the diving-with-a-guide system.

Under that definition, most of you reading this magazine are probably already technical divers - its just that some of you are more technical than others. So instead of that vague technical catch-all expression, here are some more specific definitions that might help you decide where you are and where you want to be on the Technical Curve...

This is the group that could also be termed non-technical. Its members need their diving to be as simple as possible. They might want to swim about with the fish once or twice a year, breathing air from a tank and unencumbered by too much equipment or knowledge.

Leisure divers are not required to know all the various forms of lung damage available. All they need to know is that they must never hold their breath while breathing from scuba.

Usually leisure divers do not dive deep enough (say, beyond 18m) to forfeit the opportunity to go directly back to the surface should they need to do so.

Diving around the coast of Britain and other cool countries requires a more complex approach. The water is cold and properly equipped divers normally usea drysuit.

A drysuit needs to be topped up with air from your tank to stop it compressing about you as you go deeper. Buoyancy of the suit must becontrolled, too.

The moment you add that extra hose to your regulator, the direct-feed inflation hose, you have crossed the line into technical diving

British seas have turbidity and surface conditions that put many of the best dive sites beyond the range of the simplistic approach. We quickly learn that decompression-stop diving might be needed - even if we always try to plan for no-stop dives.

So training agencies such as the BSAC and SAA teach decompression theory to every diver who leaves the starting blocks en route to self-regulated diving practice. And a diver who makes a deco stop, either real or simulated, is a technical diver.

You might argue that a technical diver is one who uses a breathing-gas other than air. I remember saying that I would never need to use nitrox. You cant teach an old dog new tricks, I thought, but I later found out that it is old dogs like me that benefit most from nitrox.

Increasing the proportion of oxygen in the air we breathe (nitrox 21) reduces the proportion of nitrogen, the problem gas that brings with it the chance of narcosis and decompression illness.

Of course, oxygen brings its own problems if you go too deep, and O2 toxicity can lead to drowning. The more oxygen in the nitrox, the less deep you can safely go. However, keep within a safe maximum operating depth and diving with nitrox is safer than with ordinary air.
An added-safety mix such as nitrox 32 could easily become the breathing gas of leisure divers in the future - even if they never get to realise it. Technical divers are the ones who understand why they are using nitrox!

Semi-closed circuit rebreather divers do not benefit from any decompression advantages over those breathing nitrox with ordinary open-circuit scuba.

However, SCRs such as those made by Dräger are an efficient way of using nitrox and they are able to provide a fixed gas duration, regardless of the divers fitness and work-rate.

Training in their use implies an understanding of the implications of rebreathing via a CO2-scrubber. SCRs therefore provide a good introduction to rebreathers for divers before they move on to closed-circuit types.

Another definition of a technical diver I have heard is one who switches regulators during a dive. This means taking one regulator out of your mouth and replacing it with another.

If you have ever used a twinset with independent regulators, you have done this whether the actual gas mixes were both nitrox 21 or not.

Many divers now enter the water armed with an independent pony bottle and regulator mounted alongside their tank. If you do this, you too are a technical diver.

Some say technical divers go deeper than non-technical divers. How deep Worldwide, most PADI-trained divers limit themselves to 18m. PADI puts a limit of 40m on recreational diving, and thats for those with a deep-diving speciality badge.

The BSAC recommends a 50m ultimate limit. Many would suggest that it is difficult to dive even to these depths without using a technical approach.

Ordinary divers used to think it safe to go to 80m with a single cylinder of air. I was one of them. A few people still go past 100m equipped in this way, but they are a dying breed!

A diver who uses air for the deepest part of his dive and then changes to progressively richer nitrox mixes to enhance the safety of, or to cut short, his decompression plan, is clearly a technical diver. We are getting into true tekkie territory now.

Our diver needs to take a selection of breathing gases with him and is careful to use the right mix at the right depth. This means going in armed with several tanks to be deployed at different stages of the dive.

He might have a travelling mix, a bottom mix and a decompression mix. A diver who uses air for a deep dive and hopes to make it back, possibly without pausing on the way up, is merely taking a big risk - not very technical.

A tiny minority of divers use a trimix made up of oxygen, nitrogen and helium to go deeper than the limit for air diving. Heliox is what professional divers use (helium, oxygen, no nitrogen, more expensive). Another mix you might come across is heliair, a trimix conveniently made by adding helium to air (oxygen and nitrogen, which stay in proportion).

These divers need to mix their gases and plan their dives meticulously, using a PC and software. Their diving is complicated because they often switch between mixes during a dive for safety. Switching to the wrong gas could be fatal, so this requires discipline.

Helium reduces the effects of nitrogen narcosis at the extreme depths to which these guys go, but it adds in the complication of additional deco-stop time needed. Trimix is used in conjunction with stage-deco techniques (see Understanding Trimix overleaf).

Then there is that growing band of closed-circuit rebreather divers. They could be seen to be the most technical of all technical divers, although in fact using a CCR is simpler than manually switching gases with open-circuit equipment.

However, a very different diving technique must be learned to use a CCR safely, which is where the complication comes in (see Are You Right For CCR).