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July 2007    Download the Entire Issue (PDF) Available to the Public Vol. 22, No. 7   RSS Feed for Undercurrent Issues
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Irrational Fear of Flashing Dive Computers

why your only fear is fear itself

from the July, 2007 issue of Undercurrent   Subscribe Now

Youre a serious diver. You read Undercurrent and know how to manage your dives with your computer, so this article really isnt for you.

But how often have you witnessed this scene? A diver has been down for 25 minutes exploring a reef, varying from about 90 feet deep to 60 feet. He checks his remaining air before beginning ascent, about 1000 psi. He looks at his dive computer and suddenly his entire body language changes. He stiffens, his kick becomes disjointed and he initiates an accelerated, urgent escape to the surface. What happened? As with some divers, he has just experienced the ultimate nightmare: His computer went into decompression. Oh my God!

It’s not a big deal if your computer puts
you in decompression mode...really.

It happens every day on liveaboards and day boats. Divers who have managed to navigate around a wreck or explore a drop-off wall face, or cruise around a sprawling coral forest to take photos suddenly react as though their doctor had told them to come in for more tests. At that point, the only thing that matters to them is getting up to shallow water as quickly as possible. That flight reaction probably is the worst possible behavior because it can trigger off-the-scale ascent rates as well as a failure to trim buoyancy. Both lapses can have them arriving in 10 feet of water and blowing right past a safety stop because they forgot to vent their BC.

Weve now escalated a benign situation into a potentially dangerous one, simply because somewhere along the line some divers have mistakenly learned to avoid decompression at all costs. Well, for folks who become apoplectic when their computer readout slides into the next color, heres the reality -- all dives are decompression dives. Get used to it.

Remember, even with dive tables (does anyone still use these throwbacks to the 1970s?), the ascent and descent rates are part of the algorithm model. Essentially, even while remaining within no stop parameters, a diver must observe the prescribed ascent rate because this will provide the off-gassing release rate within safe limits. Dive computers perform all the functions you once had to do with the tables, a pencil and paper, and they do it in real time. They analyze time at depth; ascent and descent rates; surface intervals between dives; time before flying, etc. Some also sample water temperature and breathing rate as a predictor of workload, and adjust the no-deco time accordingly. The real-time monitoring by dive computers has greatly increased diver safety by eliminating human error in time-keeping, depth recording and ascent rates.

Decompression mode is not a bad thing. Not doing required decompression is. It can ruin your day. Unfortunately, many divers have been indoctrinated to believe that decompression is something to be avoided and roughly equivalent to skydiving without a parachute. Thats simply not so. You are at no greater risk during decompression dives than you are during no-decompression dives. The key is that you complete your required decompression. Of course, you cant do a seven-minute deco stop if you dont have enough gas to breathe. However, assuming you have responsibly monitored your tank pressure, its not a big deal if your computer puts you in, or near, decompressionreally.

In most circumstances, a dive computer will clear itself of decompression obligations during your ascent. If you depart the bottom at 80 feet or so and observe the computers ascent rate (typically 30 to 60 feet per minute), you will be pleasantly surprised to see the deco stop clear as you approach the 30-foot level. Some computer models display decompression status by a reverse countdown showing minutes remaining within no-deco limits. Others use a green/ yellow/red scale to warn of status, and they may flash. No matter what display is incorporated, all computers are trying to tell you the same thing: when you may safely surface.

Too many divers Ive observed dont realize this. Theyre in yellow at 80 feet and their only option is to head for the light, jeopardizing themselves and those of us who decide to help. For example, heres a scene reported by Undercurrent reader Bud Foster (Duluth, MN), who was diving in the Turks and Caicos Islands with Dive Provo:

During the first dive, a mother-and-daughter pair stayed a little low and long on the dive, and were not on Nitrox like the rest of us. By the second dive at Black Coral Forest, the mothers computer alarm went off. She panicked and started swimming for the surface at full speed. I turned to catch her and assist (and the back of my leg rubbed up against fire coral). I got to her and offered air. She stopped and showed me that her computer was saying she was in Deco. I calmed her down and signaled for her to wait until the dive guide got to her. I showed her that her computer stated she still had 1,000 pounds of air, plus I had a buddy air bottle, and that calmed her down. Her computer was saying 24 minutes deco at 20 feet. Seconds later, the dive guide was there and sent the other guide up (after his three minute safety stop) to get another bottle with a regulator. The fire coral that had rubbed my calf felt like a matchs flame being held against my leg. I can see why people say it can make a grown man cry. I had to compose myself and keep from wanting to bolt to the surface. It seemed like the longest safety stop I had ever taken and my leg was killing me. When I got on the boat, the captain got me some solution to ease the pain, which it did, slightly.

More accident scenarios are manifested by divers who freak out and bolt for the surface. As in the case Foster described, it will only make your computer think youve lost your mind, and most models will revert to requiring more deco time since you violated the ascent rate - - a key factor in your overall outgassing and rate of release. In fact, many divers will discover that they were well within no-deco limits before doing a faster ascent. They surface with a deco obligation triggered solely by their fast ascent rate.

Making a decompression stop is simple. Dont rise above the indicated depth, establish neutral buoyancy to maintain the depth of the stop, and simply breathe normally until the time clears. Of course, a deco bar is helpful, and you can use the vessels anchor line, especially if theres a current. In fact, that 10-to15-foot safety stop you make is just a form of decompression stop. And you should, even if your computer clears you to surface. Theres no such thing as too much decompression within the last 20 feet. Hang out as long as you want. The key safety issue is completing decompression if required. Its not going to put you at greater risk.

In a perfect world, divers who are untrained in decompression techniques ought to avoid doing dive profiles that require planned decompression. But if you inadvertently go into deco, slow down and take your time. Do the slow ascent and do your stop. Thats far better than racing through the last minutes of your dive to fly to the surface to stop your computer from going into deco. Its not going to happen.

Also, your computer doesnt care if you go into deco. Its programmed to handle that very efficiently. So chill. Take the long way home, as Norah Jones sings in the song. Youll be just fine. Spend a little more time on your next surface interval if you like. Dont fret about deco, just be responsible in completing whatever is indicated and get on with enjoying the scenery.

PS: Ill bet you know someone this article will benefit. Pass it on. You might save a life.

Bret Gilliam is a 36-year veteran of the professional diving industry with more than 17,000 logged dives. He was the founder of the TDI and SDI training agencies and CEO of diving computer manufacturer UWATEC.

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