by Bret Gilliam:
The era of dive tables as the only method of calculating dive plans is one that is largely forgotten by many in the “modern” world of electronic diving computers and the plethora of algorithms and deco models that now are available.
I have long been an advocate for embracing innovation and new technologies, including being a prominent spokesperson for transitioning to dive computers, nitrox, mixed gases for deep diving, and rebreathers beginning in the late 1980s.
But my first involvement with deviations from standard practices was back in January of 1971 working on an experimental Navy deep diving project where we were assigned to film fast attack submarines in the open ocean at depths that eventually took us past 500 feet. At the time, all Navy diving was done on dive tables and there were very few choices.
We had “standard” single dive exposure, “repetitive” multi-dive exposure, “exceptional” exposure, and “heliox” that employed helium with oxygen to manage both narcosis and O2 toxicity issues. Of course, there were also tables to default to in the event of omitted decompression due to contingencies. But it was a short menu.
For the most part, these tables served us pretty well. One thing that is interesting to note is that the standard maximum oxygen partial pressure then was a PO2 of 2.0 ATA. This allowed air diving to 300 feet. Later the PO2 limits were reduced to 1.6ATA but that was derived from NOAA protocols that determined that some of the population could not tolerate higher PO2s.
In military diving when I came into the project, the governing protocols tended to be determined by the priority of the project as this was during the height of the Cold War era and making fast attack submarines as undetectable as possible was right at the top of the list. So we were encouraged to innovate as necessary to get the job done. In retrospect, it’s also worth noting that our dive team was probably considered to be “expendable” in the pecking order of achieving the outcome and we were very much aware of that in short order.
Most Navy divers were tethered and on surface supply breathing gas then except for shallow scuba work and some one atmosphere 100% O2 rebreather projects. (Of course, Sea Lab’s saturation project preceded us but the divers were basically confined within a restricted swimming range of the habitat.) We were some of the first teams that would work untethered, on self-contained multiple cylinder equipment packages and without the benefits of removal from the ocean for surface decompression. There is much to be learned from a variety of the departures from standard practice and some of the internal controversies that ensued, but the “bottom line” was the priority of the mission to get us below the deep scattering layer of ocean thermoclines (typically first encountered in the Caribbean below 500 fsw) and get the film work done for evaluation that would drive changes in nuclear submarine design to make them quieter and undetectable to the Soviets.
I was assigned to a team working in the Virgin Islands Trench, over 10,000 foot depths, while other teams were doing similar work off Andros Island in the Bahamas. Those teams included such pioneers as Jordan Klein who was also known for his Hollywood movie work on such films as “Thunderball” that featured Sean Connery’s secret agent James Bond in diving adventures.
When we learned that we would be deployed from surface vessels and would conduct our dives and subsequent long decompressions in the open ocean this initially did not raise any particular warning flags to our team. However, once we began operations we encountered a completely unexpected hazard that was off our “radar”. Everyone is probably aware of the prolific population of oceanic white tip sharks, a pelagic species known for their aggressive behavior. What we didn’t know then was that their aggressiveness was amplified by low frequency sound projections we introduced into the ocean caused by both the instruments used to calibrate various sonar devices and by the subs themselves with their own systems.
It wasn’t until many years later that the relation of low frequency sound, and other stimuli such as the noise made by sinking ships as the hulls and compartments collapsed and aircraft that crashed into the ocean, tended to drive the sharks into far more excessive threats and virtually ended any ability to thwart their aggressive attack behavior. At times, we would enter the water for routine dive system drills and encounter 10-15 oceanics and have virtually no problems with them other than curious close approaches that could be dealt with by a bang on the snout or similar actions. However, once low frequency sound and other stimuli were introduced, both their numbers and aggression tended to go off the scale.
Instead of a few sharks that generally behaved, we would now be faced with scores that could escalate into hundreds at a time. And all seemed hell-bent on biting anything they encountered. They bit the ship’s props, the prop shafts, equipment that was lowered into the water, cables that were deployed, and just about anything that entered their ocean universe. From our rather selfish perspective, we were not particularly concerned about rushes to bite the boarding ladders. But we did care about their tendencies to want to bite us… fins, tanks, camera housings, and most importantly: body parts.
There were times when it was necessary for the deck crews to hang over the working dive decks on the vessel’s sterns to push away the sharks with boat hooks just to make a “hole” in the ocean that we could jump into. It was not for the faint of heart. Once our descents were initiated, we found that the sharks would lose interest in the divers as we passed about 80-foot depths and return to abuse the vessel and its equipment. But when we came back up from deep exposures, we entered long decompression cycles that forced us into a constant war of evasive protective behavior that was more than a bit nuts.
So we began to experiment with anything that would get us out of the water faster without compromising our inherent risk and tolerance of inert breathing gas uptake that dictated our long decompression hangs to out-gas. The first thing we did was initiate contact with some civilian physiologists in Canada at a company called BioLab that were fascinated to have human subjects to beta-test some of their theories about the then largely unproven methods of changing decompression by innovations in usage of both pure oxygen and what they called “oxy-air”. This gas would later become known as “nitrox” or “enriched air”. Hell, they could have called it “magical mystery” gas as far as we were concerned if it got us out of the water faster and away from the munching predator sharks that never ceased trying to eat our equipment… and us… during the long hangs.
The first deviation from Navy protocol was to begin switching to oxygen as deep as 60 feet… a PO2 of 2.8 ATA. That exceeded the allowable maximum oxygen exposure for working divers but was exactly the same as what divers breathed if removed to the safety and comfort of a decompression chamber. We adopted a practice of as little physical exertion as possible to minimize carbon dioxide production (CO2) that was known to be a triggering influence for O2 toxicity and seizures. Our methods worked and that cut our deco hangs by as much as 50%.
The next innovation was to switch to “oxy-air” or nitrox mixes in deeper depths while adjusting the PO2 levels to our tolerance. This even more dramatically cut our deco times.
Also remember that this was January 1971, over 44 years ago. There were no cell phones, no Sat-Phones, barely any land phones on St. Croix and calling Toronto in Canada was absurdly expensive. There was no email or fax to quickly communicate the results of our daily dives and deco results so sometimes our dialogue was accomplished by “snail mail” and it could take weeks for our feedback and BioLab’s suggestions to be exchanged.
On occasions when we could get access to phones, we’d call in following a new beta-test of a suggested aggressive deco schedule and when the phone would be answered on the other end we’d detect obvious surprise that we had somehow managed to survive. But that quickly moved on to a conversation about the next suggested evolution. It was an interesting process but ultimately effective. It laid the foundational groundwork for major changes in diving.
But most importantly to our dive teams, it got us out of the water faster and away from our antagonist shark partners that we shared the ocean with.
Later, NOAA picked up where we left off and when the first generation of computers allowed algorithmic experimentation on deco models using early electronic “real time” diving computers, the revolution really took off. Much credit is owed to the late Dr. Bill Hamilton in the U.S. and the late Dr. Albert Buhlmann in Switzerland for their pioneering work in underwater physiology and deco modeling. I was pleased and proud to have known both men as friends and professional colleagues. Their work forever changed how we dive today.
Looking back on how we arrived where diving technology is today is revealing. For our dive teams nearly 45 years ago, it was prompted by adaptions aimed at self-survival and the methods worked. That’s a “bottom line” that increased our “bottom time” at depth while dramatically reducing our “hang time”.
I’m sure the oceanic white tip sharks missed us. But we were not missing our prolonged time with them…
Bret Gilliam was the founder of TDI and the other agencies of International Training. He began diving in 1958 and his professional diving career in 1971 with the Navy project. Since then he has been involved in every segment of the diving industry including retail and resorts, military and commercial operations, filmmaking, publishing, manufacturing, diving ship and liveaboard design and operations, as well as legal consulting in litigation procedures. Along the way he has logged over 18,000 dives. He was inducted into Diving’s Hall of Fame in 2012 by the AUAS as the Recipient of their NOGI Award for Diving Sports/Education. After nearly 25 years of living in the Caribbean and equatorial regions of the world, he now makes his home in Maine and travels internationally on diving projects.
by Bret Gilliam
As secret agent James Bond once sagely observed to Q, who supplied his special equipment and was complaining that he was bringing it back damaged, “It’s hell out there in the field.”
Divers aren’t dealing with jet-packs, ejection seats in Aston-Martin sports cars, or the best way to use the strangling wire released from the stem of a Rolex. But it can get a bit dicey in the field for us as well. I’m talking about the hard and grim reality of dealing with medical injuries in the middle of nowhere when facilities are not available and evacuation is not an option. If you are on a live-aboard, expedition vessel, or remote island when emergencies arise, you will have to be prepared to deal with them on-site and with the equipment on hand.
There are scores of scenarios that may present, from tropical viruses and severe stinging organisms, to lethal bites from sea snakes. But the most prevalent danger over the years has been decompression illness (DCI). If you pick up just about any diving text, medical reference, or even read DAN’s protocol for what to do when DCI manifests in a diver, the first directive will be to administer 100% oxygen by demand mask and transport the patient to a recompression chamber. Great advice. Good luck if you happen to be anchored in Chatham Bay at Cocos Island… 380 miles offshore. In Costa Rica there are no helicopters or seaplanes that can travel the distance, let alone do it round-trip, without refueling. And there is no fuel on Cocos Island. No Starbucks either, for that matter. The same is true in the Komodo Islands, Raja Ampat, or the Banda Sea in Indonesia. Think you can get to a chamber in the Solomon Islands? Oh yeah, it’s right next to the IMAX theater on Guadalcanal.
Reality is a bitch. If you or a member of your team gets bent in a remote area you will have to deal with the treatment yourself. This not only takes special training, it requires onboard-specific special equipment and trained support staff. A couple of D-cylinders in your nice little oxygen case aren’t going to get the job done.
Let’s take a quick review of DCI and what must take place to get a satisfactory outcome. First and foremost, you need oxygen. And lots of it. Secondly, you need pressure. That what’s going to crush the inert gas bubbles and let them be absorbed back into blood and tissue without occlusions and permanent physiological deficits. Time is the critical issue: the window for the most effective treatment is about one hour from the first presentation of symptoms. Tick, tock…
It must be ingrained in divers to recognize and report DCI symptoms as early as possible. Unless you are dealing with extreme exposures and incomplete decompression, symptoms will usually not present while the diver is still underwater. But upon surfacing the clock is running. This article does not have the space for a treatise on symptomatology but DCI will present as pain in the limbs or joints, or as more subtle neurological deficits initially; but central nervous system (CNS) issues will progress and can include paralysis.
Many texts distinguish DCI symptomatology into Type I (pain only) or Type II (serious symptoms, CNS involvement). To the layman or diver in the field, this distinction is not of great importance and requires special training in many instances to classify presentations. Most importantly, we want our readers to be able to recognize any symptoms or signs of DCI quickly and take immediate action.
At the first sign or symptom, the patient should immediately be placed on 100% oxygen… via demand mask. Don’t waste your time even putting a free flow mask in your gear package. You need to get the patient oxygenated. Free flow masks are wasteful of the gas, inefficient in their delivery, and you only have so much inventory of oxygen available. The therapeutic effects of 100% oxygen to a DCI victim cannot be overstated. In a significant number of cases, immediate oxygen breathing will arrest symptom progression and achieve relief without the need for recompression. But the key word here is “immediate”. Every minute lost allows for more inert gas bubbles to form and aggregate. By flooding the victim with 100% oxygen and eliminating any further intake of nitrogen from atmospheric air, you are creating a gradient for bubble size reduction and elimination. Cross your fingers and hope the victim begins recovery. You should be trained in field neurological exams and go through the checklist as soon as the diver suggests they may have DCI. Do a re-exam after the first hour of O2 breathing. If the patient’s symptoms have stabilized or improved, continue O2 administration with hourly reassessments. If you’re lucky, they may have dodged a bullet.
But you have to have an available inventory of oxygen onboard. I recommend a minimum of three H cylinders and a transfer method to the smaller cylinders commonly used with DAN O2 kits and to O2-cleaned scuba tanks because you’re going to need a lot of gas. If you’re getting results with demand mask oxygen, continue the patient’s breathing for two hours, then a 10-15 minute air break, then back on for two more hours. Follow this regimen for 12 hours and then make a complete assessment. If the patient is symptom-free, it’s probably okay to take them off O2 and confine them to a bunk for another 12 hours or so. Check urine output as well for volume and color. Cease all diving activity for 72 hours, or completely, unless they have a specific skill necessary to the project.
Now comes the tricky part: if the victim does not get better within the first hour on oxygen they probably need to be recompressed. The only way to do this is to get them in the water. This requires an in-water oxygen delivery system. Ideally, there should be an oxygen clean full-face mask available but an oxygen clean scuba regulator will do. (Full-face masks are preferred since the patient is less likely to lose their airway in the event that an oxygen induced convulsion event occurs.) Obviously, it is not desirable to attempt to place an unconscious unresponsive patient underwater. But as long as they can breathe on their own, I’d even risk this since the alternative is so dire.
In-water recompression has been around for five decades but it requires very specific training and equipment. You cannot attempt such a treatment without training. There are a variety of treatment tables that work extremely well. Some have evolved over years of experimentation and commence at shallower depths than conventional tables used in dry chambers. Other experienced contingency experts like to proceed with Table 5 that begins with a direct descent to 60 feet. But all this is predicated on oxygen supply, an oxygen clean delivery system, a conscious patient that is aware of what is happening, and several divers to rotate as underwater tenders with the patient. Most treatments will run two hours or more.
Ideally, a surface supply hose system to the patient is safest and most efficient. Air breaks also have to be factored in since a patient cannot breathe oxygen exclusively at depth. So the supply system underwater must allow for gas switches either from the surface supply hose or by changing scuba cylinders underwater.
You’re going to be underwater for a while. Proper thermal insulation for the patient is necessary as well as a fresh water hydration delivery bag or bottle. Most DCI cases manifest toward the end of the diving day and so it’s likely that a good portion of the treatment will be conducted in the dark… after sundown. Lights need to be available and the tender may also have to deal with patient anxiety. You also need to be prepared for marine life encounters. It’s unlikely that a shark will decide to chow down but the presence of predators is also a reality and the team should be prepared to ward off aggressive threats.
It all sounds more than a bit daunting. And it should. But the alternative is almost certain serious physiological damage including paralysis and death. You have to plan well in advance to have the necessary support equipment onboard and this is not easy in most third world countries. First and foremost, you have to have enough oxygen and the average live-aboard barely carries enough O2 for more than about a four-hour surface breathing period. If the operator cannot provide the other breathing delivery equipment, you may have to bring it with you. For the vessel operators that I provide operations consulting to, I recommend that they be fully prepared with all gear and staff trained to do the treatments if necessary. But these operators are few and far between. Do your advance due diligence, get proper training in field treatment contingencies, and expect to be called on to perform.
Remember: Evacuation is not an option. Without sufficient oxygen the patient has no chance. And if they don’t respond to surface oxygen breathing, there is no choice but to proceed with in-water protocols since you have to get the hyperbaric effect of pressure for inert gas bubble compression.
That’s the straight talk. Now you decide to what level you want to be prepared. There are no short cuts. TDI Headquarters can refer you to proper training professionals. This is not a dumbed-down meaningless dive specialty card. This is dead serious. I intend no pun with that last sentence…
Bret Gilliam is the founder of TDI, SDI and ERDI. He is credentialed as a Recompression Chamber Supervisor and an Instructor Trainer for Diving Medical Technicians and Physicians. He has been widely published on diving emergency medical procedures including in-water recompression. Professionally diving since 1971, he authored the diving medicine section of the reference text “Pre-Hospital Trauma Life Support” and has treated or consulted on over 200 diver treatments in his career.
By Bret C. Gilliam
A HISTORICAL PERSPECTIVE
There have been numerous articles written on the subjects of inert gas narcosis and attendant depth limitations. Many have re-hashed old formulas relating the preposterous “Martini’s Law” etc. and sanctimonious admonitions against any sport diving below 130 fsw. The authors of these materials are motivated by the best of intentions: diving safety. The problem lies in the fact that sport divers are diving deeper than 130 fsw routinely and in ever-greater numbers each year. It is important for those of us professionally involved in the sport to accept the reality of such diving practices and disseminate accurate information that adequately conveys the relative hazards and operational disciplines necessary to undertake deeper diving within the proper boundaries of responsible physiological planning and reasonable assumptions of risk. It is not sufficient to adopt attitudes of condemnation when what is clearly called for is an enlightened attempt at proper education.
It’s worth noting here that technical, cave, rebreather, and other types of exploration diving all fall, by legal definition, into the “recreational” category of diving within the U.S. This is because OSHA only recognizes three types of diving: commercial, scientific, and recreational. It’s astounding that so many professionals still errantly make a distinction between “technical” and “recreational” diving. They are the same. Argue all you wish… that’s the law. Get used to it. (“Sport” and “recreational” are interchangeable terms that refer to the same category of diving.)
As one who has practiced deep diving professionally for over four decades, I am continually dismayed at the wealth of out-of-date or incorrect information offered about narcosis. Hopefully, with more expert participants writing on the subject based on actual diving experience, a more balanced view of the subject will be shared with sport divers that will discourage them from taking unnecessary risks with improper educational resources. For those of us who actively practice deep diving in various applications, there is nothing so terrifying as the lack of proper training and materials for sport divers beyond the current existing “deep diver” programs within the mainstream certification agencies that are woefully inadequate.
Within the context of air diving, the effects of inert gas narcosis are second only to acute CNS oxygen toxicity in hazard to the scuba diver. Commonly known as “nitrogen narcosis,” this condition was first described by Junod in 1835 when he discovered divers breathing compressed air: “the functions of the brain are activated, imagination is lively, thoughts have a peculiar charm and in some persons, symptoms of intoxication are present.” Early caisson workers were occasional victims of befuddlement on otherwise simple tasks and some were reported to spontaneously burst into singing popular songs of that period. Much of the mysteries of compressed air impairment remained speculative until Benke zeroed in on elevated partial pressures of nitrogen as the culprit. His observations were reported in 1935 and depicted narcosis as “euphoric retardment of the higher mental processes and impaired neuromuscular coordination”.
Other studies confirmed this phenomena and U.S. Navy divers reported narcosis a major factor in the salvage efforts on the sunken submarine Squalus in 1939. Working in depths of 240 fsw (72.7 m) in cold water, these divers reported loss of clear thought and reasoning. Several unusual entanglement scenarios resulted and in the normal work process at least one diver was reported to unexpectedly lose consciousness underwater on the wreck. Because of this, the Navy switched to then experimental Heliox mixtures marking the first major project with this gas. Bennett (1966) first related narcosis to the Greek word “nark,” meaning numbness. The Greeks used this in association with the human reactive process to opium that produces drowsiness, stupefaction and a general feeling of well-being and lassitude.
At any rate, the best explanation appears to be the Meyer-Overton hypothesis relating the narcotic effect of an inert gas to its solubility in the lipid phase or fat. This is postulated to act as a depressant to the nervous system proportional to the gas amount going into solution. Mount (1979) has expressed the narcotic effect as determined by multiplying the solubility by the partition coefficient. By examining tables of various inert gases compared by solubility and partition coefficient it becomes abundantly clear that nitrogen is one of the least desirable gases in a breathing mixture for divers at depth. The “relative narcotic potency” is expressed as a number value with the highest number reflecting the least narcotic effect. Argon is extremely narcotic with a value of .43; Nitrogen is rated at 1.0 with Helium one of the least narcotic at 4.26.
Table: Relative Narcotic Potencies
|Helium (He)||4.26 (least narcotic)|
|Xenon (Xe)||0.039 (most narcotic)|
As experienced divers more frequently dive to deeper depths in pursuit of wreck, cave exploration and photographic interests, the subject of inert gas narcosis becomes more ardently debated. Much practical discussion of narcosis “field” theory among scuba divers was originally taken on and conducted “underground” by a close-knit community of technical professional divers without a public forum of information exchange dating back to the 1970s. Narcosis was regarded as an occupational hazard that had to be dealt with in order to gain access to new cave systems, more remote wrecks, or the most spectacular drop-off walls.
Due to the controversial nature of deep diving within the traditional sport diving industry, an understandable reluctance to discuss actual diving practices was perpetuated. Little actual “field work” was published and a word of mouth grapevine developed to compare different diving techniques in widely diverse areas. In the late 1960s and early 1970s three distinctly different segments of emerging “technical” diving were conducting deep air dives. On the cave diving scene individuals such as Sheck Exley, Tom Mount, Frank Martz, Jim Lockwood, and Dr. George Benjamin pushed ever deeper with their explorations, while Bahamian and Caribbean groups led by Neil Watson and myself pushed beyond the 400 fsw (121.2 m) barrier for the first time in open water. Simultaneously, a whole new wreck diving cult with Peter Gimble, Al Giddings Bob Hollis, Hank Keatts and Steve Bielenda was coming out of the shadows in the northeast to assault previously unreachable sites such as the Andrea Doria.
Published accounts of narcosis experiences were largely limited to cave diving newsletters, although I presented a quasi “how-to” paper on deep air methods in 1974 (Extending the Working Capability and Depth of the Scuba Diver Breathing a Compressed Air Media). This presentation at The International Conference on Underwater Education in San Diego stimulated some limited exchange of information between the diverse communities, but also focused criticism from national training agencies at the time. The “underground” once again retreated from the harsh glare of sport diver scrutiny and new breakthroughs and techniques reverted to word of mouth communications. As one veteran deep wreck explorer put it, “You can always tell a pioneer by the arrows in his back!”
In 1990 for the first time, the “technical diver” began to come out of the closet and stay a while, and in-depth discussions of narcosis went public.
Some of the earlier accounts by Cousteau (1947) relate instances of near total incapacitation at depths of only 150 fsw (45.5 m) and cite the supposed “Martini’s Law” and the classic broad generalization of “Rapture of the Deep.” In reality, the severity of impairment is drastically reduced in well equipped and experienced/adapted divers at greater depth. Narcosis is certainly a factor to be dealt with responsibly by divers, but many texts suggest levels of impairment that are far exaggerated for seasoned practitioners.
LIMITS AND OPINIONS
Today’s diver has the advantage of extremely well engineered and high performance scuba gear that can markedly increase his performance. Design evolutions in buoyancy compensating devices (BCD’s), scuba regulators, instrumentation, diving computers, less restrictive and more efficient thermal suits etc., all contribute to his ability to work deeper safely.
Of course, the use of trimix essentially negates narcosis issues, since the mix can be adjusted to match any diver’s tolerance. Also, adjustment of the oxygen fraction and resulting PO2 eliminates any threat of CNS oxygen toxicity. But air and nitrox breathing gases still predominate… in some cases simply because helium is unavailable in remote areas or financially prohibitive. Rebreathers also have emerged as reliable deep diving systems, but require extensive training just on their own “unit specific” models. Still, this is by far the most efficacious method of extending depth ranges and times underwater. More on that in another article…
I would like to emphasize that deep air diving below 218 fsw (60.6 m) is generally not recommended, given the alternatives available in today’s industry. (This depth represents the outer limits of recommended oxygen exposures for most divers at 1.6 ATA of O2.) On high risk or particularly demanding dive scenarios this depth should be adjusted shallower. As noted previously, many veteran air divers now opt for mixed gas to virtually eliminate narcosis and oxygen toxicity problems. What is the cut-off depth on air? This is clearly subjective, and must be answered by the individual diver who considers his own narcosis susceptibility, his objective and his access and financial commitment to mixed gas equipment.
Wes Skiles (deceased in 2010), a highly experienced and respected cave diver, expressed his preference for mixed gas on any penetrations below 130 fsw (39.4 m) primarily because of his admitted low tolerance for narcosis. This was back in 1990. Members of the scientific diving community still practice air dives to 190 fsw (57.6 m) officially (with far deeper dives reported “unofficially”). Mount and I have long suggested practical air limits of between 250 and 275 fsw (75.7 and 83.3 m) for properly trained and adapted professionals… but it is necessary to understand that such depths exceed the typical “working depth” guidelines for oxygen and place the diver in the O2 exceptional exposure zone. (The reader is directed to references specifically on oxygen toxicity to better understand various O2 exposure theories and phenomena.) Mixed gas solves some problems for some people, but it adds several new problems and operational considerations to the equation: expense, heat loss, extended deco times, etc. For many experienced air practitioners, deep air diving remains a viable choice simply because, done with the proper disciplines and training, it is a reasonable exercise. That is to say it can be approached with an acceptable level of risk. But new divers venturing beyond traditional sport limits must be fully cognizant of the elements of risk and that deep diving will reduce the margin for error and the attendant increased chance for injury or death must be understood. Diving within one’s limitations should be etched firmly in the deep diver’s memory. Depths below 130 fsw (39.4 m) can be safely explored, but such diving cannot be taken lightly.
Factors contributing to narcosis onset and severity include:
- Increased partial pressures of CO2 (hard work, heavy swimming etc.)
- Alcohol use or “hangover” conditions
- Work of breathing, e.g. inherent resistance within the breathing system on inhalation/exhalation cycles
- Anxiety or apprehension, FEAR
- Effects of motion sickness medications
- Rate of descent (speed of compression)
- Vertigo or spatial disorientation caused by no “up” reference such as in
- Bottomless clear “blue water” or in severely restricted visibility
- Task loading stress
- Time pressure stress
- Another lesser-known contributory factor is increased oxygen partial pressure
Narcosis can be controlled to varying degrees specific to individuals, but tolerances can change from day to day. Almost any experienced deep diver will tell you that “adaptation” to narcosis takes place. Bennett (1990) notes, “the novice diver may expect to be relatively seriously affected by nitrogen narcosis, but subjectively at least there will be improvement with experience. Frequency of exposure does seem to result in some level of adaptation.” The actual mechanics of adaptation are not clearly understood or proven but most deep divers agree that they will perform better with repeated progressively deeper penetrations on a cumulative basis.
During a series of experimental dives in 1990, I had no significant impairment at 452 fsw (137 m) for my brief exposure, approximately 4.5 minutes in the critical zone (especially for O2 tox) below 300 fsw (91 m). I was able to successfully complete a series of higher math and thought/reasoning problems while suspended at the deepest level. But this is probably the extreme end of adaptation; I dove every week for over a year, with never more than a six-day lay-off. My 627 dives during this period included 103 below 300 fsw (91 m).
For the diver who regularly faces deep exposures, a tolerance far in excess of the unadapted diver will be exhibited. A gradual work-up to increasing depths is the best recommendation. I refer to making each first dive of the day progressively deeper than the day before to build tolerances, i.e. Day 1: first dive to 150 fsw, Day 2: first dive to 175 fsw etc. Subsequent dives on Day 1 and Day 2 would be shallower than the first. This process should be over several days’ time if the diver has been away from deep diving for more than two weeks. Adaptation appears to be lost exponentially as acquired, so no immediate increased narcosis susceptibility will necessarily be evident but divers are cautioned to exercise great conservatism if any lay-off is necessitated.
THE DIVING REFLEX
Back in the mid-1800’s Paul Bert observed pronounced brachycardia (lowered heartbeat) in ducks while diving. Suk Ki Hong (1990) describes “a reflex phenomenon that is accompanied by an intense peripheral vasoconstriction, a drastic reduction in the cardiac output, and a significant reduction of 02 consumption”. Hickey and Lundgren (1984) further noted aspects of the mammalian diving reflex to include “muscular relaxation, astonishing levels of brachycardia, e.g., heart rates 13% of pre-dive levels in harbor seals… and depressed metabolism. All of these adaptations conserve the body’s energy stores.” Simply put, this reflex serves to apparently slow down most vital, internal functions such as heartbeat and shunt blood from the extremities enabling the diving seal or dolphin to more effectively utilize its single breath oxygen load while underwater.
Similar responses have been noted in human subjects. Several divers stumbled onto this in the late 1960s and began to effectively incorporate facial immersion breathing periods prior to diving. Exley and Watson practiced such techniques and I became a leading proponent of surface and ten-foot depth (3.03 m) level extended breathing with my diving mask and hood removed before dives below 300 fsw (91 m) in 1971. I have recorded dramatic reductions in my heart rate and respiration rate by following a protocol of ten minutes facial immersion breathing at the surface, then five minutes at ten to fifteen fsw (3.03 to 4.5 m) from a pony bottle. My pulse has been measured at twelve to fifteen beats per minute and respiration rate dropped to two a minute at deep depths (dive to 405 fsw/122.7 m 1977). Other divers have adopted varying uses of the diving reflex technique in conjunction with meditation disciplines with significant success. Of the divers using this technique, many report pronounced reduction of narcosis, reduced air consumption and better coordination at depth. Regardless of the scientific proof challenges, the technique is becoming more widespread and its subjective benefits certainly bear closer scrutiny.
At depth, the air we breathe has far greater density and can be an operational problem if the scuba regulator is not carefully selected to comfortably deliver adequate volumes upon demand. Breathing resistance can markedly increase onset and progression of narcosis. Until the 1990s many so-called “professional” regulator models fell sadly short on performance below 200 fsw (60.6 m).
Exhalation resistance is a prime factor in breathing control, perhaps more so than inhalation ease. Studies have shown exhalation detriments to be the most significant fatigue element in underwater breathing tests. So how do you choose between the dozens of models offered? Some benchmark can be derived from perusal of U.S. Navy test reports but sometimes results can offer inconclusive appraisals. Back in the late 1980s, the Tekna 2100 series unit basically failed the Navy tests for high performance due to its unique second stage design, but was a popular regulator with many experienced deep divers since its introduction. I used it on my record setting 452 fsw (137 m) dive in Roatan (1990) and had complete satisfaction. But remember that the numbers of regulators that are genuinely suited for deep diving are contained on a very short list. (I personally use the superlative Titanium series from Atomic since 1996.)
Now is a good time to insure that you select comparable quality instruments compatible with the depths you anticipate exploring. Keep in mind that many depth gauges and dive computers have depth limitations that will render them useless much over normal sport diving ranges. Make certain that the information is displayed in an easily understood format. If you have a hard time deciphering what you are looking at on the surface, imagine the problem at 250 fsw (75.8 m) under the influence of narcosis.
ON THE DIVE
Wreck and drop-off wall divers should use descents undertaken with a negative glide to the desired operational depth and there BCD used to quickly attain neutral buoyancy. Do not waste energy and generate CO2 using leg kicking to maintain position in the water column. Slow, deep ventilations with minimal exertions will keep C02 down and reduces onset and severity of narcosis. Narcosis has been reported subjectively to be most strong when first arriving at depth. Allow yourself a stop-activity period to monitor your instruments and let the initial narcosis effects stabilize.
Diving deep properly is more a mental exercise than a physical one. The diver must constantly be aware of his own limitations to narcosis and not hesitate to abort a dive if impairment becomes unreasonable. If narcosis is severe on descent, slow the rate or stop completely until symptoms are controlled. If possible face an “up” reference at all times such as anchor line or face the drop-off to orient the wall perpendicularly to the surface. This affords more accurate references if you are sinking or rising. If necessary, hold on to the descent line or a drop-off wall outcropping to insure of control of depth while narcosis can be evaluated.
In spite of the warnings of various academicians, it is unlikely that the diver will experience “rapture” or the uncontrollable desire to kiss a fish or dance with an imaginary mermaid. However, there is a wide range of individual susceptibility. Almost all divers will be impaired eventually. This will manifest in many ways.
Most divers are acquainted with traditional depictions of narcosis symptomatology (lightheadedness, slowed reflexes, euphoria, poor judgment, even numbness etc.). But many early symptoms are more classically subtle. Initially, divers will notice, in many cases, a reduced ability to read fine graduations in a depth gauge diving computer, or watch along with increased awareness of sensitivity to sound such as exhalation and inhalation noise. Perceptual narrowing may limit some divers to successful execution of only limited task loading. Short-term memory loss and perceptions of time can be affected. With experience, divers can learn to control these deficits to some extent. But these very real dangers cannot be underestimated. A diver unaware of his depth, bottom time or remaining air volume is about to become a statistic!
- Impaired neuromuscular coordination
- Hearing sensitivity or hallucination
- Slowed mental activity
- Decreased problem solving capacity
- Short-term memory loss or distortions
- Improper time perceptions
- Fine work deterioration
- Exaggerated movements
- Numbness and tingling in lips, face and feet
- Sense of impending blackout
- Levity or tendency to laughter
- Depressive state
- Visual hallucination or disturbances
- Perceptual narrowing
- Less tolerance to stress
- Exaggerated (oversized) handwriting
- Loss of consciousness
- Retardation of higher mental processes
- Retardation of task performances
- Slurred speech
- Poor judgment
- Slowed reaction time and reflex ability
- Loss of mechanical dexterity
Buddy teams need to be more aware of each other in deep dives. Just as frequent scanning of instruments is mandated, so is confirmation of your buddy’s status. Generally, you should look for him about every three breaths and observe him for any overt signs of impairment. Quick containment of a problem situation in its development is vital to prevent a stressful rescue event that may be difficult to perform at depth.
In 1972, I offered an effective underwater narcosis check between divers. We were frequently diving very deep with long working bottom times on this contract in the Virgin Islands. I had a secret dread of one of our team’s divers being overcome without our immediate knowledge. So I came up with a childishly simple hand signal response exercise for use at depth to detect narcosis. If one diver flashed a one-finger signal to another diver, it was expected that the diver would answer with a two-finger signal.
A two-fingered signal was answered with three-fingers; if you really wanted to screw a guy up you gave him all five fingers and then he had to use two hands to come up with a six-finger response. We reasoned that if a diver was not able to respond quickly and correctly to the signal given, then sufficient impairment was presumed to abort his dive. It worked great for us then and I still use it today. Over the years, scores of divers have reported using the “Gilliam narcosis signals” (also known as “The Finger”) with success.
Although narcosis effects are generally eliminated by ascent, it is important to understand that many divers will experience some degree of amnesia of their performance at depth. Commercial divers have reported successful completion of a work project to the diving supervisor upon ascent, only to learn later that the objective was not completed at all! Less experienced deep divers will typically not remember their greatest depth or bottom time unless disciplined to record it on a slate prior to ascent. Again, the experienced deep diver will sharply focus on his job objectives and constantly monitor his instruments. Modern devices such as dive computers greatly improve safety controls with maximum depth and time memories as well as decompression planning models.
THE MOUNT-MILNER TEST
In 1965, a research project was conducted by professional diver Tom Mount and psychiatrist Dr. Gilbert Milner to determine the effects of anticipated behavior modeling in diving students with respect to narcosis. Three control groups of four students with equal male/female ratios were trained in identical dive classes except:
Group One was taught that a diver will get narcosis at 130 fsw, and much emphasis was placed on the high probability of narcosis impairment with severe symptoms.
Group Two was taught of the existence of narcosis, the symptoms and depths of occurrence cited as beginning at 100 fsw, but were not as intimidated with narcosis manifestations.
Group Three was well educated on narcosis with three full hours of lecture on symptoms, risk, danger and known research. They were told that divers with strong will power as postulated by Miles (1961) could mentally prepare themselves and greatly reduce the effects.
Prior to the open water deep dives all students were given two dives to 30 fsw and two dives to 100 fsw to develop good breathing techniques.
Before the actual dives for testing purposes, the students were taken on a 50 fsw dive where the tests were performed so a mental/dexterity familiarity could be achieved with the format of the test problems. Changes were then made in the test so they could not be performed from memory. The tests consisted of handwriting evaluations, pegboard testing, math, and ball bearing placement in a long-necked narrow bottle etc.
In the initial test depth of 130 fsw, divers in Group One had minor-to-above-average narcosis problems while Group Two and three divers had little effect on test scores.
At the 180 fsw test depth, two Group One divers dropped from the exercise due to severe narcosis problems, and were removed from the dive. All Group Two divers were affected although still functioning at about 50% test levels. Group Three divers had minor impairment.
At the 200 fsw test depth, all divers in Group One and two from Group Two were dropped due to severe narcosis and apprehension. Group Three divers actually showed slight improvement in test scores.
At the 240 fsw test depth, one diver was dropped from Group Two and one from Group Three due to severe narcosis. The remaining Group Two diver and three Group Three divers showed levels of impairment, but again scores and performance showed improvement over the previous depth level. One diver, a female from Group Three, registered her highest scores on all tests at the 240 fsw level.
Concurrent testing of experienced deep divers showed seven out of ten divers with no decrease in performance or scores at the 200 fsw test level. The three divers with decreased performance finished the testing (two with perfect scores) but required additional time than was usual. At 240 fsw, five out of ten performed all tests with no decreased performance. One diver had problems with the ball bearing test but perfect scores on the pegboard, math and handwriting. The other two showed up to 42% deficits and had problems completing the tests.
The obvious conclusions include a subjective validation to both “adaptation” and the negative influence of “modeling” behavior in those groups of divers pre-conditioned that narcosis was inevitable and severe. The Group Three divers with little prior diving experience were satisfactorily still performing at the 200 fsw level and three divers continued to perform (with one showing improvement still) at the 240 fsw test level.
If we teach our children that all dogs will bite, we can safely assume that when presented with a specimen even as lowly as a toy poodle, we can expect a high fear index. Likewise, if we teach our dive students that narcosis is a finite, unyielding biophysical wall… then we can logically expect such conditioning to impair their performance beyond a more realistically educated diver lacking pre-conceived phobias and suggestions. Education is the key to performance and safety.
Depth limitation largely becomes a decision then based upon narcosis levels and gas supply (until the O2 toxicity range is entered). Most divers will be able to function well in excess of the so-called 130 fsw (39.4 m) limit with even a little practice.
Interestingly, the first edition of the NOAA Diving Manual published in the mid-1970s contained this notation on narcosis: “Experience, frequent exposure to deep diving, and a high degree of training may permit divers to dive on air as deep as 200 fsw (60.6 m) . . .” Although scientific diving programs and university based research groups generally advocated air diving to around this recommended limit, a significant proportion of dives were conducted in far deeper depths if necessary for observation or collection purposes, including dives beyond 300 fsw. The proliferation of “Do as I say, not as I do” mentalities still dominate all factions of the industry primarily for fear of critical condemnation by less realistic “experts”.
All divers should exercise prudence and reasonable caution in all aspects of deep diving but particularly so when it comes to narcosis. Experience is vital before attempting progressively deeper dives. Ideally, the diver should be seeking out the benefit of training by a competent, well-experienced deep diving instructor before a penetration below “entry level/open water” training diving depths. Don’t try to obtain field experience on your own or with another buddy. The historical record provides too many fatalities or near misses due to narcosis to warrant such a risk.
Many critics condemned even the discussion of practical operational narcosis planning and dismissed those of us who advocated more realistic guidelines as members of the “lunatic fringe”. Happily, most of that misguided ultra-conservatism has been withdrawn. I contend that by professionally addressing the questions of the real risks and real experiences associated with narcosis and deep diving, we will more responsibly serve today’s diver who, in many cases, is already undertaking dives beyond his ability, training and operational physiology because no proper advanced deep diver training is offered through the traditional national training agencies. Truth in education is critical to any learning process, and especially with diving. Let’s not shy away from our responsibilities as diving educators by holding fast to the naive belief that all sport diving stops at 130 fsw. For many divers, 130 fsw is a reasonable limit… but others will go deeper. They will be safer and more likely to observe a practical limit if we provide the training to better identify the real hazards and the required commitments to plan deeper diving.
Author Notes: Bret Gilliam has had a 42-year career in professional diving, logging over 18,000 dives in military, commercial, scientific, filming, and technical diving operations. He is one of the diving industry’s most successful entrepreneurs with investments in publishing, training agencies (TDI/SDI), manufacturing, resorts, dive vessels, cruise ships, and film production companies. The aggregate sale value of his multiple multi-national companies totaled over $80 million when he retired in 2005 at the age of 54.
Author of over nearly 1000 published articles, his photos have graced over 100 magazine covers, and he is principal author or contributor to over 50 books & manuals. His writing and photography has been published worldwide. He also has worked as location director, cameraman, and operations manager on scores of Hollywood movies, television series, documentaries (including National Geographic and the Cousteau series), and IMAX films.
He is a Fellow National of the elite Explorers Club and the ex-world record holder as the deepest scuba diver on conventional scuba equipment. He is also the recipient of numerous awards.
He continues a limited practice as a widely sought litigation consultant and expert witness for diving and maritime legal cases. After nearly 30 years living in the Caribbean and equatorial regions worldwide, he now lives in Maine where he divides his time between three homes and a motor yacht. He is still active in special film and publishing projects. His latest book, a large hardbound coffee table style volume, Diving Pioneers & Innovators: An In-Depth Series of Interviews, has been met with widespread enthusiasm by reviewers internationally.
He can be reached at:
54 Stonetree Rd.
Arrowsic, ME 04530