You will have seen more and more references to ''Technical Diving'' on the pages of this magazine over the past three years. When the term was first introduced its meaning was unclear and undefined and, in the U.K. in particular, there were many who declared that it brought nothing new, and that it had been with us for a long time under a different guise. If its meaning is a little clearer today, then it is because the said activity has evolved and matured during this time, and it has begun to take its place in the diving scene.
If we consider what we mean by ''Sport Diving' or ''Recreational Diving'' then we can define it as the kind of diving that is contained within a broad sphere of activities that should be enjoyable, attainable, perhaps exciting and demanding, and surely safe. It has been the aim of the training organisations, such as the BSAC, to bring people to a reasonable level of competence in this activity, always bearing in mind that diving, when considered as a leisure activity, should not expose its participants to any unecessary risk.
Now, the degree of risk is often in inverse proportion to the competence and experience of the diver. A further period of training should improve competence, and reduce risks.
It is when the type of diving being practised starts to present new problems that require new solutions, that new techniques come to be evolved. The steady progress of diving exploration is taking us beyond the more accessible inshore sites, toward less accessible sites requiring a broader range of techniques in order to maintain the required level of safety.
The training received by most divers has equipped them to undertake air diving to the limit allowed by their qualification, but in any case, not below 50m. For the vast majority of divers this is more than they should ever need. But it is, as always, the troublesome minority who have arrived at this limit and still find the need to go further who have caused the ripples that have resulted in the Technical Diving wave. This category of divers found the ''amateur diver'' description a poor fit as their needs led them to adopt techniques and equipment from the professional and military sectors, and then to evolve their own.
For many, the need arose from the pursuit of projects which slowly but surely took them outside the envelope of normal sport diving and into a new area of risk which needed a new set of solutions. This is the area which we also call ''Extended Range Diving'' since it recognises the basic needs of being able to go further, for longer, and in perhaps more extreme conditions. It is this ''professional amateur'', professional in approach, amateur in motivation, that forms the core of the Technical Diving community.
What does it involve?
Technical Diving uses a range of special techniques and equipment to extend the safe operational range and the possibilities of the diver. A principle feature is the use of gas mixtures other than plain air to reduce problems associated with nitrogen (decompression and narcosis). Initially this means breathing a Nitrox mixture which has an increased level of oxygen, and a lower level of nitrogen than normal air (21% oxygen/79%nitrogen).
A further refinement is to further reduce the nitrogen content by replacing all or part of it with another inert gas (usually helium) to reduce the narcotic effect of the mixture during deep dives.
These mixtures can be breathed using conventional SCUBA equipment, specially adapted SCUBA equipment, or rebreathers, which recycle the mixture to make full use of the oxygen it contains and to give longer duration.
Technical diving also considers carefully the selection and suitability of all the diver's equipment for more adventurous or extreme diving. Special equipment and accessories have been developed with the aim of maintaining a high level of safety while diving under more difficult conditions. The Technical Diver leaves little to chance and aims always to be prepared for any predictable emergency, usually by carrying the solution with him. This is the direct opposite of the minimalist approach preached in warm water recreational diving and should be understood as having quite different objectives.
Techniques have been developed to ensure safe diving during penetration of wrecks, deep into underground cave systems and for diving under ice; a set of conditions grouped under the description ''Overhead Environments''. Diving into a situation where you cannot make a direct ascent to the surface presents a host of additional problems and gives new urgency to the problems of managing your gas supply. Once you go beyond the reach of natural light you have to rely on the illumination you can carry with you, and you have to concern yourself minutely with the question of navigating your way in, and more importantly out, of the cavity.
Other techniques have been evolved to allow extended in-water decompression procedures to be carried out in greater safety and with greater efficiency. Longer decompression procedures can underline the need for improved thermal insulation, beyond that required on normal dives.
The passage from normal sports diving to Technical Diving does not commit you to runningthe full gamut of the possibilities available. It allows you to acquire a few more tools and techniques to make the kind of diving you intend to do safer and more satisfying. The better understanding gained may make your normal air diving safer and more interesting.
What are the advantages?
For most divers the passage into Technical country starts with nitrox. The advantage we are looking for from nitrox is longer no-stop times, or shorter decompression stops. By reducing the proportion of nitrogen in our breathing mixture we will absorb less nitrogen during the dive and have less nitrogen to eliminate during the ascent. For a given mixture we can calculate, or read from a table, the Equivalent Air Depth (EAD). This is the depth at which we would have the same PPN2 if we were diving on air.Thus our no-stop limit at 30m using air and the BSAC'88 table A is 20 minutes, but if we use EANx36 we will have an EAD of 24m so we can extend it to 30 minutes.
Alternatively, if we want to spend 40 minutes dive time at 30m on air we will need to make stops of 1 minute at 9m, and 9 minutes at 6m. On EANx36 we would need only 1 minute at 6m. (Note: this will only work for the first dive using current BSAC'88 tables since the surface interval is carried out on air, a different gas to that used during the dive).
A ''nitrox dive'' could be a dive carried out almost entirely on air, perhaps in the 40-45m range, for which air is quite suitable, with a nitrox mixture (probably between 50% and 80% oxygen, or even pure oxygen) used only during the decompression stops. This will still give faster elimination of nitrogen and shorter decompression times.
Another approach to improving your safety margin is to dive on nitrox, but to treat it as air for decompression purposes. To enjoy this benefit you breathe nitrox during the dive or the decompression stops, or both, but use your usual air decompression table or air dive computer to control your decompression procedure.This is an approach which could have an appeal to the more careful, older, less fit, or less frequent diver as it allows you to keep comfortably within the recognised safety limits.
Should you have one of the latest generation of nitrox dive computers then you can gain all the benefits of reduced nitrogen intake due to the gas breathed, along with those due to a possible multi-level dive profile. Before the dive you enter into the computer the oxygen percentage of your gas mix and the computer deduces the balance to be nitrogen, and calculates the decompression requirement accordingly. Naturally, it will work equally well for air diving. A nitrox computer has the added advantage of tracking your oxygen exposure to ensure that you do not exceed the recommended CNS toxicity limits.
It has been suggested that the use of nitrox reduces the narcosis effect, but there is no scientific evidence to support this. The solution to the narcosis problem is trimix, which reduces the narcotic effect of nitrogen by replacing a part of it with helium.
Another observation is that diving on nitrox results in a lower consumption rate, since the diver enjoys a higher PPO2 during the dive, but this has not yet been demonstrated scientifically.
What are the problems?
While reducing the nitrogen content brings some advantages; increasing the oxygen content introduces some new problems. We have all learned that oxygen becomes toxic when breathed at higher partial pressures, and that at 66m normal air has reached the maximum recommended limit of 1.6 bar PPO2. When we take the advised limit of 1.45 bar then we find that EANx32 has a maximum depth limit of 35m, EANx36 is limited to 30m, and air to 59m. Clearly, nitrox is not a gas for deep diving.
An additional problem represented by oxygen is that it can have a toxic effect on our Central Nervous System if we are exposed to higher concentrations over longer periods. For normal recreational dives the required exposures are longer than we are likely to meet, but can be built up over a series of dives. If we are diving to 30m on EANx36 (PPO2 =1.44) then our maximum exposure should not exceed 120 minutes at that depth, which would give us a number of other problems as well (gas supply, decompression times, cooling). Over the course of 24 hours our time spent at this PPO2 should not exceed 180 minutes. These exposure times get substantially longer at lower PPO2 levels.
Oxygen in high concentrations can also give problems in its handling and use. Oxygen has the property of supporting combustion, although it is not itself flammable. When it comes into contact with certain substances, such as hydrocarbons at high pressure, there is a risk of explosion. Any part of our diving equipment which stands a chance of coming into direct contact with high concentrations of oxygen must therefore be scrupulously clean and free from any such contamination. The first candidate is our diving cylinder which, along with its valve, must be cleaned for oxygen use, known as 'in oxygen service', since the procedure for filling it with nitrox could start by introducing a quantity of pure oxygen into the cylinder. Our standard air regulator should be suitable for use with nitrox mixtures containing up to 40% oxygen, but if we wish to use it for higher concentrations, such as decompression mixes, then this too must be cleaned for oxygen use and never used with normal air.
What we need to do to go deeper is reduce the oxygen content, to avoid toxicity problems, and reduce the nitrogen content, to avoid narcosis problems. This usually means making up the balance with helium. Now while helium helps considerably with the narcosis problems of deep diving, it brings no decompresssion advantage, and will even increase decompression times on shorter recreational dive exposures. For deeper diving we can continue to reduce the oxygen content, and replace all of the nitrogen with helium, to give a mixture called Heliox. Unfortunately such a Trimix or Heliox deep-diving mixture would have such a low oxygen content that it would be unsafe at shallower depths.
Helium has two major disadvantages; it is horribly expensive, and it cools you down faster than when breathing air. Thus trimix and heliox diving bring additional problems of cooling, which are further aggravated by the longer decompression times involved.
As we can see, there is almost an optimum mixture for each depth range, depending on how long you need to stay, and the thermal factors. The well organised Technical Diver will carry a travel mix suitable for breathing from the surface down to a reasonable depth, and will then switch to a bottom mix, lower in oxygen content, for the time at depth, and during the return to the surface will have to switch back to the travel mix, with the additional possibility of a decompression mix, with an even higher oxygen content to give optimal nitrogen elimination, for breathing during the shallower decompresssion stops,.
Just in case this sounds simple to some of you, you may not have grasped the complexity of a dive which relies on identifying and breathing from the correct regulator, attached to the correct cylinder, for precise phases of the dive, while always ensuring that you have enough of each of the required gases available and in reserve for each phase.
The problem of carrying large amounts of gas with you on a dive is a real one. The best solution is to use the gas more efficiently, and that means to rebreathe it so that the oxygen content is used more fully. A rebreather used with normal air (21% oxygen) allows each breath to be recycled about four times as only about 5% is used during the respiratory cycle. A set fitted with a standard 10 litre cylinder would last about as long as a twin 2 x 20 litre set on open circuit. Alternatively, a much smaller cylinder can be carried, and if this is filled with Nitrox, then even greater gas efficiency can be achieved. Rebreathers therefore achieve major efficiencies in gas usage, but have a high initial cost. They also demand far greater care and attention, and considerable maintenance, compared with SCUBA.
We have mentioned in passing a number of commodities, the gases and mixtures, which are not yet easily available, and are all more expensive than compressed air. Dive centres equipped to fill your dedicated nitrox cylinder with the appropriate mixture are still few in number, and this will only change as a result of increased demand. A fully-equipped mixed gas blending system requires a major investment on the part of the filling station. Alternative methods of providing the gas mixtures exist, but they too are logistically more complex than simple air filling, and this must be reflected in the cost. Nitrox is usually the result of adding a prescribed amount of oxygen to air, and breathing oxygen is a gas which is relatively easy to obtain and not unreasonable in price. Once helium enters the scene then the price of a fill escalates. A helium mix can cost as much as 20 times the price of compressed air. But in a closed circuit mix rebreather the amount of helium actually consumed is very low, making it economical once more.
What training is available?
If you are already a diver, a BSAC Sport Diver, CMAS 2 Star Diver or equivalent, with some additional experience then you have the base required. If your qualification is higher than this, then that can only give you an advantage. However, in all cases there will be material to be covered which you have not met before, as well as some useful revision of things which you should remember from earlier training.
Where should you go for this training? If you are a BSAC member, then you will soon be offered (end of 1995) Skill Development Courses leading to BSAC Nitrox Diver and BSAC Advanced Nitrox Diver. The Extended Range Diver course is also in hand.
An alternative choice is to go to one of the specialist agencies : IANTD (International Association of Nitrox and Technical Divers), TDI (Technical Diving International), or ANDI (American Nitrox Divers Inc.). They all offer a path starting with nitrox diving and continuing through other Technical Diving courses toward Trimix use, and eventually Rebreathers.
These are the early days of rebreather training for amateurs and the specialists are now developing their training courses. However, the pattern of first understanding how rebreathers work in general terms, and then going on to learn how to use a specific set, seems to have been adopted. Most of the rebreather manufacturers have contracted with one or other of the specialist agencies to supply the training for their equipment, and it will often be packaged with the equipment cost since no sale will be made to uncertified divers. Given the high cost of the equipment, it is likely that courses will also be available for divers who wish to qualify as users so that they can hire the equipment for those special expeditions.
A good starting point would be ''An Introduction to Technical Diving' by Rob Palmer, available from the Diver Bookshop, £17.95.
If you are a travelling diver then it is worth noting that CMAS (World Underwater Federation) should soon have international equivalents available for a Basic Nitrox Diver and an Advanced Nitrox Diver. This will allow their member organisations (BSAC, TDI, IANTD, etc.) to apply for equivalents to their certificates for issuing to their members. A degree of cross-recognition of certificates will soon be in place between these organisations.
Should I get involved?
Just answer these simple questions :
1. Do you feel the need to lengthen the no-stop times of your dives in the 20-35m range?
2. Do you regularly do dives with long decompressions in the 20-35m range?
3. Do you feel a need to increase your safety margin beyond that which you practise currently?
4. Do you accept that you will probably have to dedicate one or two cylinders and one or two regulators for nitrox-only use?
5. Are you ready to accept strict maximum depth limits on your dives?
6. Do you accept the need for some additional specialised training, whatever your current level?
7. Do your long term aims include silent, bubble-free, constant buoyancy diving?
If you answered 'yes' to at least three of these questions, then it is time you started considering taking the first steps.
If you answered 'yes' to 5 or 6 questions, then you have probably already started, or are about to.
Whatever you decide now, we are bound to see a continuing evolution in the techniques and possibilities offered by new diving technologies, and there will always be new developments to convince you that the time has come to take a step forward.
It is generally accepted that breathing Nitrox mixtures on open circuit SCUBA equipment may not give you the result you need for some of the more serious diving projects. However, it provides a valuable bridge from sport diving techniques and disciplines to the more advanced techniques and stricter disciplines required for trimix and rebreather diving. Although considered a major step today, Nitrox will probably come to be considered a standard recreational diving gas within a few years.
What are the objectives?
Although the immediate objective is to benefit from the advantages offered by nitrox, in all its applications, the main attraction in following the Technical Diving path is to make the leap to rebreather technology.
The attractions of the rebreather probably outweigh for most of us any trifling problems such as cost. The first rebreathers to be offered to the non-commercial, non-military diver will seem to be highly priced, but will surely come down in price as they gain in popularity. Prices quoted today range from £5000 to £10000 for different specifications. But if you count the cost of a fully rigged technical diver's kit it too soon achieves horrific proportions. And don't forget the real economies in gas cost per dive that are possible with the rebreather. But most of all, consider the advantages of a relatively light-weight and compact set which gives you silent, bubble-free, constant buoyancy diving, the dream of every photographer and marine biologist.
Although the cost of specialised rebreather training will probably be part of the package in most cases, it is a real factor for would-be rebreather divers. Adequate familiarity with the equipment needs at least a week of training before the proud new owner, or renter, can be let loose with the equipment.
In summary, the objectives of Technical Diver Training should be to give the diver a wider range of techniques and knowledge so that the right choices and decisions can be made for each dive, with never a need to compromise on safety. The techniques and disciplines acquired should not encourage the diver to undertake greater risks, but rather to reduce the risk through a more thorough approach to planning and executing a dive.
Although the activity places a heavy emphasis on equipment and technology, none of this will be of any use if the diver does not first accept the need to approach it with the right attitude. Do not expect the passage to Technical Diving to be an easy one; it is intended to make you careful, responsible, thorough, fastidious, and aware of your new limits. You will find yourself more often at the limits of our knowledge on diving physiology; the more experts you meet, the more often you will hear the reply ''We don't know, yet.''
Take care when exploring the frontiers, it is all too easy to stray from the beaten path.
Some definitions.
ANDI : American Nitrox Divers Inc.
CMAS : Confédération Mondiale des Activités Subaquatiques - World Underwater Federation.
EAD : Equivalent Air depth.
Heliox : A breathing gas mixture containing oxygen and helium
IANTD : International Association of Nitrox and Technical Divers. (IANTD UK, 42 Marsh Road, Thatcham, Berks RG13 3QR.
Nitrox : Also know as 'oxygen-enriched air', 'Safe-Air' (registered to ANDI), EANx (Enriched Air Nitrox). A gas mixture containing nitrogen and oxygen, where the oxygen content exceeds that of normal air (21%). Generally expressed as Nitrox XX, or EANxXX, where XX indicates the percentage of oxygen in the mixture.
PPO2 : partial pressure of oxygen in the mixture breathed. BSAC recommended limit for this is 1.40 bar for in water use. Overall recommended limit by all agencies is 1.4 bar
PPN2 : partial pressure of nitrogen in the mixture breathed.
TDI : Technical Diving International.
Trimix : A breathing gas mixture containing oxygen, nitrogen, and helium.
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