By John Adsit
Editor, Curriculum & Instruction
[Note: ETCJ editors and writers live full lives, and from time to time, we’ll be publishing some of their extracurricular pursuits. See Jess Knott’s “Smackademia – the Best of Both Worlds!,” the second in this series. -Editor]
I made my first online class in 1995, and since those days much of my life has been spent trying to convince nonbelievers that computers could improve student learning if used properly. Those years were filled with many less than pleasant arguments, and like many people I looked to my recreational life to get away from such battles. Unfortunately, I now find that my chief area of recreation, scuba diving, is filled with those same battles. The controversy of my work life has doggedly pursued me into my recreational life.
My most recent pursuit is cave diving. Cave diving is an intoxicating sport. People ask what you see down there, and the stock answer, “wet rocks,” does not convey the magic of that subterranean landscape. That magic comes with a price, though, for cave diving is by far the most dangerous of all forms of diving. The labyrinthine passageways in the total darkness of caves demand complex navigation skills, and divers must be able to pass through small passageways with fine silt beneath them without stirring the mud and creating a “silt-out” that even their powerful lights cannot penetrate. Although most caves have guidelines in the most difficult passageways, it is easy to miss a turn and find yourself in an unexpected side passage with no clear idea of where you are. If divers are too far into a cave when their air supply runs low, they have no chance of survival.
Because I want to enjoy that special beauty and live to talk about it, I want to be fully alert to everything I must do to be the safest diver I can be. That puts me in the middle of a great diving controversy, and that controversy, surprisingly enough, is in the use of computers.
More than a century ago, John Haldane theorized that decompression sickness (“the bends”) could be prevented by ascending slowly and stopping briefly at specified depths, depending upon how deep people had been and how long they had stayed there. This would allow the nitrogen that had been built up under pressure in the tissues to escape safely without forming bubbles with potentially crippling or fatal consequences. He tested his theory on goats and made a table to guide safe ascents from depths. Later research led to refinements and newer versions, but the tables that are used today are still mostly direct descendants of his original goat-inspired tables.
Dive computers came along in the 1980s and caught on quickly. They did the table calculations for decompression for you, eliminating the need for tables and providing many other benefits. Most importantly, the diver carried them on the dive itself, so the computer could constantly recalculate the dive as depth and time changed, giving the diver a much more accurate analysis of the dive and (especially) guideline for ascent. Today, using computers to track decompression needs is the norm for what we call recreational divers.
By recreational diver, I mean 90% of the world’s divers, people whose depths, times, and locations are limited enough so that at any time they should be able to make a safe, direct ascent to the surface. This is contrasted with what many people call “technical diving,” which I will broadly define as diving for which a direct ascent to the surface is not a safe option, if it is an option at all. The diver may have gone so deep or dived so long that extensive decompression stops are required, or the diver may have entered a cave or a shipwreck, where a physical barrier prevents that ascent.
Technical diving has needs beyond the normal recreational diver. Technical divers rarely breathe air as we know it. Because nitrogen has a narcotic effect (nitrogen narcosis) at deeper depths, they often breathe a mixture of gases that replaces some of the nitrogen with helium. Because oxygen becomes toxic under the pressures brought on by increasing depths and can cause a seizure, deep diving often demands mixes with less oxygen than would support life on the surface. Conversely, as divers ascend and do decompression stops at shallower depths, they are better served by mixes with more oxygen in them. On a deep technical dive, then, a diver will at times breathe from different tanks with different mixes of gases.
The computers used by recreational divers have no value to a technical diver because they cannot deal with the complex needs of that sport. Although almost all recreational computers can adjust to the level of oxygen in the gas they are breathing, few can track more than one level on a dive, and none can do calculations for mixes with helium. They do not have algorithms truly designed to plan decompression schedules following extended deep dives. Only a few companies make the kind of computers that will meet the needs of technical divers.
So what has this to do with my world? In recreational diving, I am an instructor who gets to tell students what they should do. In technical diving, I am a student who must follow the dictates of my instructors. Therein lies my problem, for my instructors are in the opposite camps of the great computing controversy.
My primary training agency, UTD, does not believe in computers at all. They believe only in a very basic computer called a bottom timer, which gives little more than time and depth of the dive. Divers anticipate the depth and time and calculate a decompression schedule based on a formula. If the actual dive varies from that plan, they recalculate “on the fly” and follow that new plan. All the planning for the dive is done in the diver’s head, either before the dive or during the dive. UTD does not trust computers, and their instructors tell divers to use the computer between their ears instead.
So that was my training prior to starting my cave diving training. I did many dives to depths and times far beyond the normal recreational limits, switching gas mixes on long decompression ascents. My teammates and I planned and executed those dives using the formula taught by our instructor.
Although UTD offers cave instruction, I decided to do my cave training with a different agency, the NSS-CDS. In contrast to UTD, my cave instructor very much wants me to use a computer, and he does not trust the one between my ears. Having only a useless recreational computer at my disposal, for my initial training I borrowed a computer that could handle the multiple gases I would be using. I was quite glad I did. Although I also carried my bottom timer and could have calculated a decompression schedule if I needed to, I had plenty to think about while learning cave skills, and I was quite happy to glance at the computer while ascending to see how long I would have to be breathing oxygen when I switched to it to complete my decompression schedule.
Devotees of the no computer school of technical diving don’t mind doing all that arithmetic at depth. In an online debate on the subject, one said that doing those calculations gave him something to think about while he was diving. In response, John Chatterton, the star of the Deep Sea Detectives series, said he already had plenty to think about while he was diving (usually exploring deep wrecks) and was happy to follow his computer to the surface when he was done.
The no computer crowd argues that it is dangerous to follow a computer on something as important as a decompression schedule because the computer can be wrong and you would not know it. Computer users respond that even with a helium mix, a diver may have enough of a narcosis effect to skew thinking and make a miscalculation. Indeed, on one incident not long ago divers miscalculated their decompression obligation to a degree that was embarrassing to talk about once on land, and they suffered decompression sickness as a result. In another incident a few months ago, divers in Florida without computers to tell them when to ascend totally miscalculated their decompression needs and waited far too long, with the result that one of them is now a quadriplegic.
So I live in two worlds now, one that ridicules computers and one that uses them faithfully. For my cave training, I am more than happy to let a computer help me with my dive. When I am exiting a cave, I want to be totally focused on my exit route and the actions of my teammates, especially in case a silt-out obscures my vision and sends me groping for a life-saving guideline. Yes, I have the skill to make those calculations if I should ever need to, but that is something I will prefer to do only if needed. In my last cave exit, I was nearly climbing up through a narrow passageway, and I was as focused as I could be on finding the best possible path out. I would prefer not to be doing math problems at the same time. I am now what NSS-CDS calls an Apprentice Cave Diver, and when I return to the underworld to get my Full Cave certification, I expect to bring a computer of my own.
On the other hand, when I am with my team doing other technical diving, I will hide that new computer to avoid the ridicule that is sure to accompany its use. Or perhaps I will admit its existence and put it into “gauge mode,” shutting off all those functions that are so nice to have as I navigate a cave and turning it into an expensive bottom timer.
What I won’t do is fight the battle. I have enough of that to do in my regular world.
Acknowledgement: I am extremely indebted to Jill Heinerth, one of the world’s greatest cave diving photographers, for her generous permission to use photographs from her most recent project for this article. The pictures were taken February 24, 2010 in Dan’s Cave in Abaco in the Bahamas. See Jill in action in the Bahamas in the PBS Nova Special on Extreme Cave Diving. -JA
Filed under: Uncategorized | Tagged: Apprentice Cave Diver, bends, bottom timer, Cave diving, cave instructor, decompression, decompression sickness, Deep Sea Detectives, Dive computer, divers, Full Cave certification, helium, John Chatterton, John Haldane, narcosis, nitrogen, NSS-CDS, oxygen, recreational diver, silt-out, technical diving, UTD |