Important note: This article was first composed during 1992-1993, when technical diving started to become popular. Since then, many aspects of equipement and practice evolved tremendously. For instance, deep air diving is now seen as an unacceptable practice by many experts. Several training agencies updated their programs in regard with deep air diving.

Note from the author:

For the last few years, and now more than ever, we are facing a "high-tech" revolution. Most sport diving magazines have published articles on Enriched Air Nitrox (EAN), mixed gas and deep diving. Certain magazines have opted for presenting the maximum possible amount of information (enclosed in a section dedicated to advanced diving) while other are much more conservative.As a result, more and more divers are becoming interrested in imitating technical divers and consequently, the diving accident rate could increase dramatically over the coming years. It is no longer rare that students in an advanced diving course question the depth limits imposed by recreational diving associations. This is perfectly understandable when we read the accounts of divers who theoretically should be dead1 in recreational diving magazines. Personally, I have recently seen in a magazine, an advertisement for a diving association which trains divers to dive to 300 feet on air! It will now be essential to adequately teach the appropriate recreational training limits and the reasons for these limits.

In the past, diving was taught in a rigorous military fashion. Divers were produced with impressive physical and technical abilities, but their attitudes were less a preoccupation. One can recall that diving was known as a dangerous sport ant divers themselves were often identified as part of a "macho" population. The performance and safety of equipement used during the past (up-stream regulators with low flow rates, horse collar or no BC at all, and inefficient thermal protection) was inferior in comparison to the type of equipement available today.Next, the recreational diving associations modified their way of teaching and other associations were created. These training agencies, including ACUC gave great importance to the divers attitude toward safety and they espoused a continuing diver education program. In addition, they recognized convenient limits for the type of equipment and techniques used in recreational diving. Among others, these education programs prepared divers to perform safe non-decompression dives to the depths of 100 or 130 feet.This initiative has had a spectacular effect on our sport. The accident rate plunged and more and more people became interrested in diving. DAN, the CMAS and others even obtained insurance policies covering, at resonable costs, the transport and treatment of diving accident victims. DAN has recently published the fact that the accident rate for recreational diving is now only 0.03%, the same as for bowling, although the severity of the accidents are not comparable.Now we face a new phenomenon: Certain recreational divers feel that they are too controlled, and as mentioned in the introduction, they have access to a great deal of information and many accounts of divers surpassing the established safe limits of sport diving. Luckily, only a small percentage (approximately 10%) of the sport diving community is interested in deep diving. In contrast, those who dive deep, expose themselves to risks for which they were not prepared during their training. Most of this group are totally ignorant of the risks involved and appropriate techniques, while others erroneously identify themselves as a new category of divers: the "technical" divers2. It was funny (or disappointing), last November, to see a customer coming in a dive shop with a pony bottle attached to his standard tank, and proclaiming himself as a Hi-Tech diver because of that.

Before resuming the controversy actually going on over this type of diving, we must first define "technical diving". This activity involves a series of diving specialties for which the recreational diver is not prepared. These specialties include dives or combinations of dives in the following categories: deeper than 130 feet diving, cavern, cave and wreck penetration, decompression diving, use of special gas mixture (including Heliox, Trimix, Enriched Air Nitrox, Oxygen, Argon and others) for the working (diving) phase and the decompression phase of a dive. Technical diving is practiced using unorthodox equipment in unconventional (for the sport diver) and non-intuitive method with which the recreational diver is unfamiliar. The costs for this type of diving are also uncommon. The cost of gas for each technical dive may vary from $30 to over $200, compared to $5 for a conventional sport dive. It is well known that a complete set of diving equipment costs slightly over $2000. The technical diver, however must spend from $6,000 up to more than $10,000 to practice the activity with an acceptable safety level.Technical diving is a highly controversial form of diving. Certain associations recognize that these type dives are possible, but prefer that recreational divers lean as little as possible on the subject. In addition, several diving and medical authorities have simply condemned certain types of technical diving (such as diving deeper than 130 feet on air and decompression diving). The argument contends that the technical diver does not have the technical support required for this type of diving. In effect, technical divers rarely have a mean of verbal communication either with their team members or with a surface tender. In addition and contrary to commercial divers, technical divers rarely have access to a recompression chamber at the dive site.Several physicians assert that it is unsafe to dive deeper than 130 feet while breathing compressed air due to the effects of nitrogen narcosis. According to David Sawatzky M.D.3, certain divers may learn to improve their performance while under the narcotic effects of Nitrogen. These divers seem to slow down and concentrate on the task at hand, effectively compensating for their reduced cerebral function. If they are experienced, they may execute the required tasks but they require more time than on the surface. Very experienced divers may therefore routinely dive to over 130 feet and perform with an acceptable degree of effiency. However, according to Dr Sawatzky, they may be incapable of reacting appropriately when confronted with a new situation or an emergency. Consequently, they risk possible death through the inability to take the proper decision.The community of technical divers recognizes the dangers of Nitrogen (or inert) gas narcosis but judges that one may be adequately prepared to face most situations through rigorous training and certain advanced techniques. In fact, technically speaking, the maximal depth limit for air breathing according to the US Navy, the DCIEM and the NOAA is in the range of 180 to 190 feet. Note that according to Dr Peter B. Benett4, absolutely no confidence whatsoever may be accorded to the performance of human beings breathing compressed air below this depth. In addition, in order to avoid an accident caused by Oxygen toxicity5, technical divers generally limit their Oxygen exposure to 1.4 ATA which corresponds roughly to the depth of 190 feet while breathing compressed air.As far as support for the technical diver versus the commercial diver is concerned, the community acknowledges that certain safety elements could be improved. It is however, noteworthy that "full face" masks fitted with a communication system are now becoming popular while certain technical diving circles have procured portable recompression chamber (i.e.: S.O.S. Hyperlite) for the modest sum of $30,000US. While one recognizes that the ideal situation may be difficult to attain, technical divers feel that it is now possible to perform deep decompression dives with an acceptable safety level. Thanks to new technologies, it is now, more than ever, possible to safely and comfortably remain underwater (mandatory during decompression or penetration dives). Let me describe some specific equipment which has been perfected to a level sufficient to assure diver's safety. It must be noted that the specialized equipment used by technical divers is not limited to the following:

Regulators:

Many regulators now have performance characteristics which exceed military standards. It is essential to have high performance regulators (at least two of them) to reduce the effort of inspiration and expiration at great depth. Paired with good breathing and diving techniques, it helps avoid a high level of CO2 which can affect the degree of narcosis and the sensitivity to Oxygen toxicity at depth.Also available are full face masks with integrated regulators5 which offer divers comfort, safety and a mean of communication.

Valves:

Technical divers dive with a minimum of two high performance sources of air. Valve systems now permit one to connect two or more tanks to any regulator as well as to shut down any given regulator at any time. In addition, one may isolate any tank in order to limit air loss in case of equipment failure such as a broken valve or a burst over pressure disc.The best valve system assemblies are sealed by flexible "O" rings and not by metal-to-metal contact. This helps to avoid catastrophic air loss if damaged by impact during the dive. These valves may be completely opened or closed by turning the handle 1½ turns.

Tanks:

With the latest developments regarding compressed air cylinders (OMS, Beuchat and other cylinder companies), a diver can easily transport large quantities of air or other gas (even more than 400 cubic foot) so that technical dives may be accomplished with a reasonable safety margin. Technical divers usually plan 1/3 to 1/2 of their gas for dealing with possible emergency (they try to avoid being a victim of the Murphy's law as much as possible).Closed circuit technology is now available to technical divers. Soon, sport divers will gain access to these rebreathers that allow 6 to 12 hours of dive time, regardless the depth. Such rebreathers weight less than a double tank setup.

Thermal Protection (Dry Suits and Underwears):

The dry suits currently available do keep the diver quite dry. Certain top of the line models are very rugged and may protect the diver in case of contact with sharp objects (in a cave or a wreck for example). High quality undergarments made of Thinsulate® (developed by 3M) have good insulative qualities even when wet. Technical divers also use special gas to inflate their dry suits. This gas, heavier and more dense than air has better insulative qualities than air.

Buoyancy Compensators:

Because of the quantity of equipment required for technical dives, these divers must have large capacity BC (40 to 60 pounds of lift). The dry suit is not considered as sufficient for safe diving with a double-rig. In order to satisfy the needs of cave divers and other technical divers, a few companies have developed dorsal style compensators which provide better tilt control and diver balance underwater. On a "heavy" dive, a diver may wear two compensators7. A couple of manufacturers are now presenting dual bag/inflator compensators for added redundancy and safety.

Other Equipment:

Emergency decompression reels/liftbags, surface supplied decompression gas, high intensity lights, Jon lines, dive planning software and laptop computer... are also part of most technical dives. In addition, technical dives require a lot of redundancy (lights, knives, masks, air/gas sources, weight, decompression line, gauges...) in order to manage every possible failure.

Decompression Gas:

Technical divers generally decompress using Enriched Air Nitrox (typically EAN 50) and pure Oxygen (or recently, EAN 80). Even though the use of these gases present an increased risk during handling, the probability of DCI (Decompression Illness) is greatly reduced. Theoretically, the duration of decompression stops may be shortened when one breathes a gas which contains less inert gas (note that some studies suggest that Argox would be better than pure O2 in some cases - Anderson et al., 1991). Technical divers generally follow standard air decompression schedules (when diving on air) and therefore seem to give themselves a considerable safety margin.

Whatever the theoretical or practical capacities of the diver and no matter what quantity of equipement used, deep diving involves many additional risks. The following information may be used during an advanced or deep diving course to help understand the limits of recreational diving.

Nitrogen Narcosis

As was previously stated, it is unlikely that one could react appropriately in an emergency while under the effects of Nitrogen narcosis. In addition, "stress" radically accentuates these effects and may instantaneously extinguish the divers judgmental capacities. For example, in 1988 a team of three divers planned a 130 feet dive in a quarry. At 100 feet, one of the divers signaled that he was feeling the effect of N2 narcosis and decided to stop his descent. The team leader signaled this diver to wait while he went to retreive the other diver. Upon his arrival at 130 feet, he looked up to check on the first diver, who had disappeared! Nacorsis had hit him instantaneously but did not prevent the team leader to recognize it and initiate the ascent. Despite the fact that his buyoyancy was negative, he never thought to inflate his dry suit! When he checked his depth gauge, about one minute later, he was at 145 feet. He ascended by climbing the quarry wall with his hands. Fortunately, no accident occured during this dive and the divers all did their decompression stops together. It is obvious that this dive team mentionned was much more fortunate than the other one which dove the Oka quarry (in Québec) on October 17, 1990.

The Decompression Sickness

The statistics available through the Divers Alert Network, illustrate that the probability of a DCS hit increases radically when the diver descends deeper than 80 feet (although many believe that lack of proper training is the most important factor). When one uses a dive table or a dive computer, he (she) must question the risk of decompression illness at which that table places him (her). For example, the non-decompression limits of the US Navy table carry a risk which varies between 2% and 5% for no-decompression dives deeper than 40 feet. That is to say that 1 diver out of 45 would suffer from a DCS following a 100 feet/25 min. (square profile) dive and that 1 diver out of 23 woudl have a DCS following a dive to 200 feet! It is important to note that the risk increase with repetitive diving and with dives involving decompression (it may attain 50% following extreme exposure dives - i.e.: long decompression or deeper dives).The DCIEM tables give us better results with a risk of 1% for dives with short decompressions and a risk factor of 5% to 10% for extreme exposure dives. It is important to note that the DCIEM Sport Diving Tables should not be used for planning decompression dives. It is preferable to obtain the DCIEM diving manual which contains the complete decompression tables.Certain divers use diving computers thinking that they are perfectly safe. In DAN's 1988 accident report it may be found that the number of diving accidents among the computer users is particularly high. This may be explained by the fact that once a diver acquires a computer, he (she) changes his (her) way of diving; he (she) dives deeper, makes reverse profile multi-level dives and conducts reverse profile repetitive dives.Even though computers seem to be as conservative as the Canadian tables (UWATEC computers such as the US Divers Monitor, Beuchat Aladin, Parkway and others, provide no-decompression limits comparable to those of the DCIEM tables), this is not always the case. For example, the computers listed above (using a modified Bülmann's ZHL-16 algorithm) require a decompression time of 28 minutes for a 30 minute dive at 130 feet. The DCIEM standard air table require a decompression time of 38 minutes for the same dive; 10 minutes more decompression time.The DCIEM tables involve a risk factor of 1% to 3% for this type of dive. For recreational diving, this is already too high. That is why it is essential to make safety stops and to avoid making mandatory decompression dives. Technical divers use Oxygen and/or Enriched Air during dives which require more than 20 minutes decompression in order to reduce the risk of DCS.A decompression accident may not only have physical consequences (temporary or permanent injury or death) but also psychological consequences8. This type of accident could be likened to the STD of aquatic sports! The affected diver certainly feels guilty, accused and rejected from the diving community. More importantly if he (she) has surpassed the established limits for which he (she) has been trained.

Besides the problem of Nitrogen narcosis and decompression illness, the diver must realize that he (she) is quite far from the surface when diving deep. At 130 feet, the surface is at least 2 minutes and 10 seconds away, provided that no decompression is necessary. All the problems which may be encountered underwater must be solved quickly on site (both physical, mental and equipment problems).

All recreational diver training agencies have established maximal depth limits for sport divers. The depth limit of 130 feet has received world-wide acceptance and the depth limit of 100 feet is considered reasonable in Canada due to our environmental conditions.It is generally known that an advanced diving course prepares divers for the maximal depth of 100 feet while divers may learn to dive to depth of 100 to 130 feet by taking a specialty course in deep diving. This course will provide them with the additional knowledge on decompression theories, physic and physiology of diving, Nitrogen narcosis, specialized equipment, stress management, gas management, emergency procedures and decompression techniques, etc.It is important to specify that no sport diving training course at any level prepare a diver to dive outside the recreational diving limits. Nor an Open Water diver, a Divemaster or a Master Instructor are prepared to venture into advanced deep decompression dives using their sport diving knowledge.Certain specialized training agencies now offer courses in technical diving. One may find programs which teach deep air diving to 190 feet (IANTD) or 300 feet (PSA), Enriched Air diving (i.e.: Technical Nitrox), Mixed Gas diving (Heliox or Trimix), Cave and Shipwreck penetration diving, and others. The table below summarizes those training agencies and their course offerings.

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This article is absolutely not intended to be a promotion of technical diving. The most important thing to retain is that recreational diving limits are well founded. These limits have been established upon the capabilities of sports divers with good "watermanship" using equipment, techniques and knowledge provided during their training. Fundamentally, these limits represent the levels at which divers may gain maximal pleasure from diving while minimizing the risk of accidents.There will always be certain divers who wish to go further. Some will risk their lives on order to establish records while other choose to go deeper to explore wrecks, caverns, reefs or sea bottom that most divers have not seen, stepped or damaged.Those who decide to learn on their own may probably to it more slowly but if they make one or two mistakes, the chances are that they will be out of luck (like hundreds of divers now deceased).

1) Many magazines have published the account of Bret Gilliam who broke the air deep diving record in 1990. Mr. Gilliam descended to 452 feet using a 100 cubic feet tank of compressed air.

2) Technical diving was certainly born at the same moment as SCUBA diving itself, but has only been publicized as such recently in popular magazines.

3) See the text NSS Cave Diving Manual, pages 157-160 for Dr Sawatzky's explanation of inert gas narcosis.

4) "At depth greater than 180 feet (6.5 ATA), no trust should be placed in human performance or efficiency while breathing compressed air", Peter B. Bennett, "Inert Gas Narcosis & HPNS", in Diving Medicine.

5) See article "Oxygen Toxicity Reviewed" by Michel Therrien in Contact March 1993.

6) The AGA Divator and the Diving Systems International EXO-26 are the full face masks generally used by technical divers.

7) With four steel 95 cf tanks and special suit gas, a diver would be negative without even wearing a weight belt! A primary BC with a lift capacity of at least 50 pounds plus a secondary BC are required for a safer dive.

8) The reader is invited to read the article entitled "Straightening Out the Bends - Ongoing Research on the Social Reaction and Stigma Surrounding Decompression Illness" in the "Bent" issue of AquaCorps - The Journal For Technical Diving.