Maltas deep wrecks, out of bounds for sport divers, tend to be in good condition, being dived less and protected from rough weather.

WHERE IS HE Paranoia is setting in. Our instructor is capable of anything. Will he be shutting the twin-set down Is he going to rip our masks off Simulate free-flow problems by pushing our purge buttons Or perhaps he will just do it all at once
We are in the middle of a simulated deco dive, carrying twin-sets and stage tanks. Ascent is imminent in the runtime schedule now and we have,
so far, managed to avoid major complications. All has gone to plan.
We are acutely aware, however, that the purpose of this dive is to present our group with complex problems in order to evaluate our ability to solve them under stress. I scan around for Magnus, our instructor, but he is nowhere to be seen, so I reciprocate the up signal my two co-students have given me.
The moment my thumb goes up, my air supply is shut down. I catch Magnuss shadow in the corner of my eye as he moves away from the valves on my twin-set behind me.
I realise that switching to my alternative air source, suspended from a bungee cord around my neck, will not help. That too will be cut off.
I signal a huge out-of-air signal to Gary, who immediately offers his long-hose regulator from his mouth, while simultaneously changing to his spare, also placed under his chin.
Every action is carried out without stress or panic but, phew, does it feel great to have a working regulator back in my mouth!
So far, so good. We turn to Morten to start a joint ascent, but find that his mask has gone missing without trace!
Still breathing from Garys long hose, I grab Morten to support him as he digs an extra mask out of his thigh pocket and slips it on. With this sorted out we are finally ready to carry on up to the simulated deco-stops ahead of us.
Behind in our plan now, we will have to readjust as we go along.
I wonder what challenges lie ahead before we break the surface of the salty Mediterranean once again.

The whole alphabet
The concept of trimix diving is simple enough. As with air and nitrox, it is basically about breathing. In and out. In and out.
But along with the greater depths to which this triple gas grants access go longer decompression stops, on which two, perhaps three different deco gases are needed along with the bottom gas.
This is when the ability to deal with a series of complicated scenarios becomes essential, and when trimix divers must prove themselves to be not only self-sufficient but team-players.
Sport divers can interrupt a dive at any time, and only really need a plan B if things go wrong. Trimix divers, on the other hand, need most of the alphabet.
Our technical diving course is taking place in Malta. The waters just outside the capital, Valletta, hold a wealth of wrecks ideal for this purpose.
More than a dozen rest between 40-60m, a mere 15-20 minutes RIB ride from shore - aircraft, minelayers, destroyers, steamers, tugboats, passenger vessels and freighters.
Most of them shared the fate of being shot to pieces in 1942 by the German Army, when it controlled Valletta.
Technical diving at this level is a team sport, and it makes no sense to do the course on your own. Ideally you should find one or more buddies at your own level or above.
I had headhunted Morten, an old friend, knowing that he would be
a competent buddy. We decided to learn as much theory as possible from home (which is in Sweden) to minimise school-bench time in Malta.
Chris Etzerodt from TDI Scandinavia agreed to go through the teaching materials with us and prepare us well for the practical exercises.
The referral principle, when a course begins in one location and is completed in another, does not seem to be widespread in the area of technical diving. But with Chris and our instructor from Oxygène Malta, the Swede Magnus Grinneback, both present at the Copenhagen Dive Show in January, a meeting between the two was possible. This allowed us to plan every step of the course together, for both theory and practicals, ensuring that all course standards would be kept.

The theory curriculum in TDI Trimix Diver is comprehensive, but the manual is rumoured to be inferior to the one for TDI Advanced Trimix Diver.
Chris already had a couple of students doing the full trimix course, so we were upgraded to theory lessons based on the better manual, even though our course title remained TDI Trimix Diver.
A fair few spring tides have come and gone since I completed my first technical diving course six or seven years ago. The courses were fewer and farther between then, and the manuals pretty awful.
As technical diving courses have increased in popularity, so have the finances behind them, resulting in improved educational tools. However, even today there is room for improvement before tekkie manuals can match the quality of PADIs course material.
The TDI manual features poor black and white printing with a graphic quality bordering on sloppy but, appearance apart, it is logically structured, well-written and has a concluding control-question in every section, just like the PADI manuals.
Theory lectures mainly revolve around dive-planning, using the same modus operandi as in sport diving.
In basic diving courses students learn to plan dives using tables, a skill that often becomes rusty after certification and adoption of dive computers.
This is also the case in trimix diving, where most participants use either advanced trimix multi-gas computers or PC-based planning software such as V-Planner, GAP or Deco Planner. These technological aids are a great help in keeping track of all the parameters associated with technical diving.
To start off, theory lectures are packed with button-pushing calculator exercises and exasperating formula-crunching.
This is for figuring out gas usage down to the last decimal for each phase of a dive. But it soon starts to feel pointless to expend this amount of effort, knowing that all you have to do is punch your RMV (Respiratory Minute Volume) into your deco software to have your gas needs calculated automatically. It is as if were using an abacus instead of an Excel spreadsheet.
Still, the point is taken: to make use of PC applications in a safe and efficient manner, we need to know the principles of advanced dive planning.
Unfortunately for TDI instructors and students alike, however, tools to make this process more painless seem to be lacking. A chart for registering runtime schedules would, for example, make it easier to keep track of the many numbers.
We wrap up the theory lessons with an open-book exam, where students are allowed to consult their tables, formulas and notes for answers.
Students who have stayed attentive in class, taken comprehensive notes and revised to a reasonable degree will not find the exam overly complicated. They may even find it as interesting as we did.

Excess baggage
It has taken a few years, I admit, but I seem to have mastered it now: the art of packing my sport-diving gear and underwater camera along with a couple of T-shirts, shorts and other bits and pieces while staying under the magical 20kg weight limit.
This, however, becomes an outright impossibility when travelling with technical dive equipment. Drysuit, four regs, wing, backplate, two torches, line wheel plus the extras add up rapidly. This is why we decided to pre-order 15kg of excess baggage allowance, which turned out to be sufficient.
Most airlines do not accept luggage pieces weighing more than 32kg apiece, so it is recommended that you pack several smaller bags instead.
This is also helpful when lugging bags to and from the airport.
The first day of the course in Malta was taken up with theory revision, but this time we focus on practical dive-planning. Everything becomes much more fun when you are planning the dive youre about to go on, especially without the use of tables, formulas and calculators.
Working with three gases, trimix on the bottom, one weak and one strong deco gas, parameters quickly add up and become difficult to keep track of.
Even if this kind of planning is possible using tables and formulae, fatal mistakes are easily made. Calculations based on software rather than tables result in dive-planning that is more precise, and optimally customised for local conditions.
We used V-Planner, both in a laptop version and on a handy pocket-sized PDA version. It turned out to be a good idea to calculate the plans through two different platforms, as our results differed a fair deal in the beginning.
It was not until we figured out that one version had a different base configuration that we got them to show identical decompression plans. The take-home message: be extremely careful when using deco software. You need to be 100% aware of how the programs think, and how changing any one factor might affect the total picture.
It is important to think for oneself and to scrutinise all results: Does that sound right Can that really be it Shouldnt the 15m stop be a minute longer The applications are only as smart as the people using them.
Trimix diving should be planned involving the whole team, so that whether a plan makes sense and feels right can be discussed. This is possible only through a strong understanding of theory and the principles on which it is based. In addition to these skills, you need to have a keen interest in the latest developments in the subject.

Practical skills
Up next in the course are the practical skills. Few of the exercises are unique to the trimix course - similar ones are used in Advanced Nitrox, Tec Rec and other decompression courses and are all about problem-solving and the handling of emergency situations.
Perhaps this familiarity was why it didnt feel like too big a challenge to shut down the tanks behind my neck, turn the isolation manifold between the twin-set, inflate and release SMBs, unhook and mount stage tanks, share air via the long hose, or conduct buddy-breathing from the stages.
Naturally, all exercises have to be carried out with perfect neutral buoyancy and without shifting around too much in the water, with or without wearing a mask. Our instructor made sure that we had a good command of all these skills, and we identified areas where our equipment needed reconfiguring.
A D-ring placed a couple of centimetres off can make it extremely difficult to attach a stage tank, just as a harness a little too tight can make it impossible for a diver to turn round and reach the valve to shut down a free-flowing tank.
So preparing for a technical dive is, more than anything, a case of improving and re-adjusting even the tiniest details.
Fills, gas-analysis and tank-labelling also take time. But messing around with equipment can be a fun part of technical diving, all part of the satisfaction of fine-tuning everything.
After the simulated deco-dive, where we were to react to the rigged problems that, thanks to Magnus, were bound to arise, we are finally ready for a proper trimix dive the following day.

A telling-off
Our first real trimix dive is to take place on the Hellespont, a fine war wreck located at moderate depth. At 42m we need only 20% helium in the mix to achieve a markedly lower narcosis than we would have on air or nitrox.
This dive could be executed as a normal (if short) sport dive. However, with the options available to us in case of emergency, the greatly extended bottom time and strongly reduced narcosis clearly illustrate the advantages of trimix - lower stress levels, greater enjoyment and far greater safety.
The dive is a success, but the way we handle the deco phase doesnt exactly result in gold stars from our instructor. In fact, we receive a well-deserved telling-off for our behaviour!
One of the most important procedures when using accelerated decompression is to ensure that you are using the right gas at the right depth.
All deco tanks are labelled with a number to indicate their maximum operating depth (MOD).
We brought two deco gases, nitrox 50 (MOD 21m) and pure oxygen (MOD 6m) and it could have been fatal to breathe from the wrong one. For example, if we used the oxygen stage tank by mistake at 21m, we would have been at severe risk of oxygen toxicity.
This is why divers should verify each others gas changes. Again, teamwork and co-ordination are vital to this, and Magnus is right to be unhappy with the way we handled the switches - far too slow and simply too sloppy.
Also, we didnt quite manage to synchronise our ascent which, inevitably, makes it difficult to check any gas-switches with your buddies.
It was during the evaluation of our teamwork efforts, or lack thereof, that we realised the problem. As experienced divers and instructors we were just a little too used to looking after ourselves, and we behaved more like three solo divers than anything else.
Of course, diving in a threesome, its easy to overlook one person. We need a different approach, appointing Gary
as team-leader. After all, he is familiar with local conditions and has the most dives under his belt with our current equipment set-up.
We also agree on tighter procedures for gas switches and methods of clearer communication. Then we practise one dry run after another, in order to feel comfortable with the switches.
Over the next couple of days, everything is fine-tuned to perfection.

Narcosis depth
On the final and concluding deco dive we had hoped to visit Le Polynesien, one of the finest wrecks in the Med. Unfortunately, weather conditions force us to remain closer to land. Our alternative is the minesweeper Eddy, at a final resting depth of nearly 60m.
A bottom time of 25 minutes is going to cost us 40 minutes of deco - a total runtime of 65 minutes. We use trimix 18/35 (18% oxygen, 35% helium, the rest nitrogen). The stages are once again loaded with 50% and 100% oxygen.
Our intellectual abilities would effectively have been reduced to zero had we been diving the same maximum depth of 60m on air.
However, 18/35 enables us to move our equivalent nitrogen depth (END) up to 32m, meaning that carrying 35% helium in the trimix for a 60m dive is the equivalent of a 32m dive on air.
An END of 32 might be suitable for regular wreck-diving, where you swim around and enjoy it all, but if you want to photograph objects or perform other assignments where a higher level of fine-scale movement, co-ordination and concentration is required, an even lower END might be a good idea.
I certainly feel the old machinery slow down a bit inside my head, even if I am breathing trimix. The dive is perfect, and back on land we congratulate ourselves on gaining new, valuable experiences and completing the course successfully.
We will also return home with a number of world-class wreck dives in the bag.
Trimix is a brilliant tool and all dives below 30-35m should theoretically be carried out with a lesser or greater amount of helium in the cylinder.
Unfortunately the relatively high price of helium is always likely to limit its popularity, and the price is unlikely to improve.
Still, weak trimix mixes at moderate depths need not cost more than a couple of tenners, and if that isnt money well spent, what is The thing is, not only will you be diving safer dives on trimix but you will probably also recall more of the experience afterwards. How about that for a great pay-off

Trimix courses
The technical diving agencies such as TDI, IANTD, DSAT/PADI and GUE have slightly different names for their respective trimix courses, although they are all typically divided into two levels.
The first is often called Entry Level, Normoxic, or simply Trimix, and generally has a maximum depth of around 60m. Courses in this category are based on a trimix breathable all the way to the surface, due to the oxygen content of no less than 18%.
The next level, typically referred to as Advanced Trimix or Full Trimix, has bottom gases with such low oxygen contents that they cannot be used from the surface and give a maximum depth of around 100m.
To do a trimix course, one typically needs to have Advanced Nitrox Diver or an equivalent certificate, be comfortable with twin-set decompression diving and accelerated decompression.
While admittance requirements may also include a minimum number of dives, most instructors will prefer to do a personal evaluation of potential candidates, as well as testing their skills in the water, before admitting them to a course.
There is no reason for trimix to be used exclusively by technical divers on technical dives. IANTD has recently launched the concept of Recreational Trimix, aimed at advanced sport divers who fancy using it as a tool for reducing narcosis levels at moderate depths, or as an introduction to higher-level technical diving.

  • Oxygene Diving ( charges around 560 for the TDI Trimix Diver course and can fix up accommodation. Tony Backhurst Scuba Travel (01483 271765, is offering a low-season package from 795 until 27 March 2008. This includes the four-day course with manuals, certification and gases; seven nights B&B (twin-sharing) at the 3* Hotel Roma in Sliema; and flights from Gatwick and UK regional airports with Air Malta (35kg baggage allowance). An upgrade to the 4* Hotel Fortina can be specified.

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    If you run out of bottom gas your buddy will offer you the long-hose regulator from his mouth and switch to his alternative air source.
    Trimix demands methods that are more precise than when diving on air or nitrox. Gar and Morten pose on a deep stop as instructor Magnus Grinneback watches.
    The Oxygéne diving centre is well- placed for diving the many wrecks near Valletta. Details are checked and the gas analysed as the four divers wait for the boat - between them they will have 17 tanks in the water.
    A runtime plan is strapped to the arm, and the dive computer is in gauge mode, showing time and depth only in order to prevent it from calculating decompression.

    Accelerated decompression: The use of one or more gases with a high oxygen content to achieve shorter decompression times.
    Bottom gas: The gas used at the bottom, typically air, nitrox or trimix, unless the dive is exceptionally deep.
    Deco gas: Decompression-phase gas.
    END: Equivalent Nitrogen Depth, the narcosis level of trimix compared to that of air.
    Gas switch: The procedure of changing from one gas to another during ascent, to achieve as efficient a decompression as possible.
    MOD: Maximum Operating Depth, the greatest depth at which it is safe to breathe the gas.
    Multi-gas computer: A dive computer for calculating the consequences of gas switches mid-dive.
    Nitrox: Breathing gas with a higher content of oxygen than air, used as bottom gas at moderate depths and as deco gas for accelerated decompression.
    Normoxic trimix: Trimix mixture with more than 18% oxygen, making it breathable all the way to the surface.
    Runtime: Total dive times, at the bottom and at deco stops, added together as a running plan. Generated by deco software, it can be considered a tailor-made table, for what to do and when.
    RMV: Respiratory Minute Volume - a divers gas consumption at a given depth.
    Stage tanks: Cylinders containing decompression gas. Typically made out of aluminium and therefore relatively neutral in the water, they do not affect the positive buoyancy of a diver, even if left behind during the dive.
    Trimix: A mixture of three gases, oxygen, helium and nitrogen. Helium lessens narcosis and is easier to breathe at depth. The drawback is that it is relatively costly and demands highly precise diving procedures.