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tech talk Text by Steve Lewis, with thanks to Neal W. Pollock, Ph.D., Research Director, Divers Alert Network Photos by Andrey Bizyukin and Benjamin Martinez One might be forgiven for assuming that as a certified diver, one would understand the science and common- sense behind the basic guide- lines governing our approach to decompression stress. After all, a good part of a diver’s ini- tial training (and, hopefully, much of the curriculum for more complex programs), explained the vagaries of breathing compressed gas underwater. Decompression Safety for Recreational Divers However, there seems to be a huge gap between the average diver’s approach to decompres- sion stress, and that approach in a “perfect world”. But I can’t— Mybe computer saysbent I did everything right The issue with diving— at least for this BENJAMIN MARTINEZ discussion —is that as a diver descends in the water column, he or she has no the stored inert gas is released by the When diving, tracking and under- a bad-luck day, we run a higher than fatigue, mild joint pain and dizziness all option but to breathe compressed gas. diver’s body. This is called inert gas elimi- standing how to best manage inert gas usual risk of suffering decompression sick- the way through paralysis and death. Because of this, the inert gas contained nation, or more simply, decompression. uptake and decompression within safe ness (DCS). Getting bent, the colloquial The uptake/elimination cycle is in whatever is being breathed is stored in These two processes are part of every limits, is second only to making sure term for DCS, is a collection of disorders complex and quirky. For example, it’s the diver’s body. This is sometimes called dive—even seemingly benign sport dives one has something other than water to caused by a portion of the inert gas believed the speed of inert gas uptake is inert gas uptake. to shallow depths for short periods of breathe. If we “get it wrong” and remain stored in a diver’s body bubbling out of different (faster) than the speed of inert At the end of a dive, on the way back time. Every dive really is a decompression at depth too long, ascend too rapidly, solution too rapidly. The consequences of gas elimination; but this is theory rather to the surface, the process is reversed, dive. breathe the wrong gas, or simply have being bent run the gamut from nausea, than proven fact. 83 X-RAY MAG : 63 : 2014 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO tech talk ... a computer, even when used cor- rectly, provides no more than super- Safe Deco ficial protection from DCS—just authority that the very first-level of information. because of its com- We need to dig a little deeper into plexity and variabil- what affects decompression... ity, DCS is the bête noire of divers and signs diving. It certainly Accepting the ever-present risk of DCS or scares the beje- and understanding the erratic character symptoms. sus out of me, and of this risk, is a pre-requisite of becoming Adding yet many of the men a responsible and informed diver, regard- another compli- and women who are less of whether your dives take you to 10 cation is that there are my dive buddies. metres or 100 metres, or last for 20 min- simply dozens of dive In the vast major- utes or 200. computers on the market ity of recreational A personal dive computer—like any and several substantially dif- dives, the inert gas computer, big or small—is very good at ferent decompression algorithms in question is nitro- crunching numbers. It excels at calculat- at their core. Indeed, some models of gen, but when a ing gas uptake based on depth, time PDC are capable of running second inert gas is and breathing mix; and, with the help more than one algorithm, introduced into the of a decompression algorithm, showing and often those running the the breathing mix—heli- users how fast or slow to ascend, where same algorithm interpret its type of um for example—a to stop in the water column, and for suggestions for gas uptake information whole new array how long. However, this is all theoreti- and elimination differ- that is going to of complications cal. Decompression theory is just that; ently. This makes it close help you stay safe on is unleased. Diving and a decompression algorithm is simply to impossible to give use- your dive. Absolutely with two breathing a mathematical model that postulates ful suggestions detailing have as an end goal gases—oxygen and what happens to in a diver’s body when the pros of each and how of your “getting to nitrogen—presents us he or she is diving. That’s right, deco the- to work around the cons. know you” session, decompression chal- ory is woven throughout with guesswork: Nevertheless, there are a understanding what lenges: diving with some of it informed, some not so much few recommendations algorithm your com- three magnifies the so. that apply to PDC use puter uses, how to adjust challenge consider- The shortcoming of any decompres- generally. its conservatism factors, and ably. sion algorithm and therefore of any dive the potential effects of more computer is that the relevance of its Do’s and don’ts or less conservatism on you and Dive computers calculations to you and me are limited 1. Read the user’s your health. An ally in the fight for because it cannot adequately account manual. Have the information about for the numerous biophysical variables computer beside 2. Use it according to the guide- and a better under- particular to us as individual divers. You you as you do so. lines in the user manual and ANDREY BIZYUKIN standing of gas and I may be similar perhaps, but cer- Get to know what whatever common-sense you Not only are uptake and elimination uptake and elimination is the dive com- tainly we are not the same. We can wear your new tool is have been gifted with. In attempts most likely to NOT be lineal mirror-images puter. the same brand and model of PDC and capable of to reset their PDC because of a of each other, several other variables Personal dive computers (PDCs) have dive very similar profiles breathing the and how recent transgression (usually some- are thought to play important roles in the evolved astonishingly rapidly in the past same flavor of nitrox (or trimix), but the to acti- thing that came close to getting the uptake/elimination processes as well. I 20 years. The current generation does a two of us will most certainly on-gas and vate any user bent), I have witnessed divers used the phrase, “are thought to play very good job of tracking the mathemat- off-gas at different speeds and with dif- bells and pulling out batteries, hanging com- important roles”, because the variables— ical prediction of inert gas uptake and ferent levels of efficiency. And those dif- whistles it puters in the water “to decompress,” the bio-physical processes at play within elimination even when the person wear- ferences will vary from day-to-day, dive- may be fitted and even leaving their PDC on the a diver’s body—are complex and not ing the device is diving deep, for long to-dive. with. Learn boat for a dive to “cool off.” None of completely understood. periods of time, and breathing multiple As a direct result of this, you and I what button this is a good idea. Seriously. In a word, the factors governing flavors of gas. However, a PDC offers no could well go diving together tomorrow does what decompression safety are effectively iron-clad safe-guard that its user will not morning and one of us might get bent and how 3. All late generation dive computers capricious. We might say with some suffer a DCS episode. while the other is completely free of any to access deliver warnings when their users mis- 84 X-RAY MAG : 63 : 2014 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO tech talk behave. These take the form of audi- ble alarms (bells and buzzers) or visual warnings flashing colors, changing colors on output screens, symbols or messages. Some combine both visual and audible warnings. However yours is designed to deliver cautions to the diver, take note of what it “says” and modify your behavior accordingly. I once shared a decompression sta- tion and an annoyingly long stop with someone whose PDC chirped cease- lessly at him (and anyone else within earshot). He had NOT read the user’s The Australasia-wide perpetual manual before the dive, and there- fore was unable to switch it to make photo and video shootout adjustments to the ascent schedule with close to US$100,000 in prizes! for any of the three decompression ANDREY BIZYUKIN gases being used on the dive. While The Underwater Project (UP) is the A few new features of the UP are: • If you have been participating in the the whole dive team was hanging protection from DCS—just the very ing a “magic silver bullet” capable of world’s fi rst perpetual underwater Underwater Festival in previous years, • A great new fully featured out at six metres or so, his computer first-level of information. We need to protecting us completely from DCS. shootout competition. your past entries will become part of wanted him to return to 30 metres dig a little deeper into what affects He also suggests that often divers snapshot map your portfolio An evolution from seven years as the • Every member will get their own • Members can choose for entries to be and start a whole new decompres- decompression, and understand a who suffer DCS look for some way to Underwater Festival, the UP continues stunning portfolio site with used by non-profi ts for conservation sion schedule.

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