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Decompression Diving

1. We've learned that every dive is a decompression dive. You on-gas; you off-gas. Surface with too much of the former and not enough of the latter: You're bent. Safety stops are a decompression stop. Slow ascents are a decompression technique. You're a decompression diver, like it or not.

2. We like it. There's no reason that with proper training, skills and equipment recreational divers can't employ this legitimate technique for maximizing hard-earned diving dollars. Especially considering the next reason:

3. We're wired. Virtually all of today's dive computers provide the information you need to plan and execute simple forms of decompression diving. Some computers do it with graphic displays and flashing icons. Some talk us through it.

4. We're stupid. Boiled down, decompression is a relatively simple procedure. You ascend to a given depth and hang out for a period of time prescribed by your computer, then go up another 3 metre/10 feet and zone out again. Try not to fall asleep. But don't be fooled: At some point, a few curve balls will get tossed your way and the best laid plans take a turn south. That's why the key to responsible decompression dives is planning and preparing for the things that can go wrong.

What's Wrong With This Picture?

Most divers are never taught proper deco technique in traditional diving courses. And that's fine since PADI, SDI, SSI, NAUI and others do not consider planned decompression as part of their charter. Safety stops receive strong mention, but little attention is paid to precision and accuracy. Consequently, watching many sport divers do safety stops is like trying to follow a yo-yo in action. You can get away with that kind of sloppy technique in safety stops because they aren't required for the dive profile.

But with planned decompression, stops are factored into the overall dive profile. If you decide to take your 9 meter stop at 6 meter or 3 meter, the odds are you may get to experience the reality of decompression sickness firsthand.

Planning

Method 1: Use dive tables to predict a dive profile that includes required decompression stops. This allows advance planning for "bottom gas" (what you will need to breathe during the working portion of the dive) and "deco gas" (which you'll need to complete the decompression). Given this scenario, the diver can easily compute a schedule that will allow him to carry enough gas supply for both portions

dive. Indeed, most tables published for sport diving assume that any deco will be made on the same stuff that the diver was breathing while he was swimming about on the reef or around a wreck.

However, most divers planning decompression today look for an additional safety edge by using pure oxygen or a nitrox mix to increase the efficiency of off-gassing. These divers carry a smaller cylinder of "deco gas" to switch to, usually around the 6 meter stop, or they use one provided by the dive boat.

Method 2: Plan the dive and the decompression as it occurs. This is done with dive computers and allows a much greater window of flexibility to the dive plan since no rigid profile is set in advance. The governing factor in this type of plan is to allow enough gas to complete whatever decompression may be required. There are endless variations to gas volume management that can be calculated by the diver under water, including the classic cave diving "rule of thirds" (one-third of your gas for the descent and dive, one-third for the ascent and decompression, and one-third for reserve).

Method 3: Divers using secondary deco cylinders have an extra edge on the folks who want to decompress on the remaining air in their primary tanks. Not only will they benefit from the higher oxygen mix, they will also generally have from 3 liter to 8 liter of additional gas to breathe during the hang.

Tips for Avoiding the Chamber

So you completed your dive and are ready to head up to begin the decompression indicated. Here are some basic do's and don’ts.

Know your computer. If you haven't thoroughly familiarized yourself with your computer's decompression functions, don't even think about trying a deco dive just to see what happens. Some units will default if no-decompression profiles are exceeded. Others will scramble if you venture beyond a certain depth limit. Still others have deco models so conservative that you will spend more time at 3 meters than you spent in line at the DMV.

Monitor ascent rate. Your ascent is part of your total decompression profile. If it's supposed to take you two minutes to come up to your first stop, don't do it in 30 seconds. Likewise, don't come up unreasonably slow as this will only increase nitrogen gas loading during the deeper part of the ascent. Your computer should remind you if you ascend too quickly for its deco model by either flashing a warning on its display or beeping at you with an audible signal.

Control your buoyancy. Stay in control by dumping excess air during the ascent, and stop completely at least 3 meters below the first stop to ensure you can hover comfortably. Dive with extra weight to counteract the positive buoyancy of tanks as they are empty.

Stay static. Preferably, your first experiences should include some type of static support like an anchor line or deco bar. This also gives you a firm handhold if current is present or if the dive boat is swinging on its mooring.

Use the KISS system. Keep it simple stupid. Initially, no decompression should be planned with more than one stop until you are completely comfortable with your ability to maintain depth, predict breathing rate, and manage your gauges.

Do it all. Never cut a decompression stop short. Spend all the time required at the depth prescribed. It's OK to extend the last stop. You can consider that part of your "safety stop."

Deco Diving—The Real Risks

Over the years, the mainstream diving community has shunned stage-decompression diving by sport divers, resulting in a significant stigma surrounding the practice. The fact is: Many, if not most, shop owners and instructors do not have an adequate understanding of stage-decompression diving and its risks. The risk of DCS for a diver properly executing a stage-decompression dive is probably about the same, if not less, than it is for a diver making a no-stop dive because of more efficient off-gassing, thus minimizing "silent" bubbles formed during ascent. Less risk of DCS, however, does not mean that the stage-decompression diver does not face other significant risks. Stage-decompression divers are forced to stay below a virtual ceiling or face a high risk of DCS. Therefore, they must carry additional equipment that allows them to solve problems at depth, because surfacing is not an acceptable option.

Risk — Dealing with this gear on a dive boat results in a higher risk of physical injury.

Risk — The extra gear results in a larger profile while diving, creating an increased risk of overexertion due to swimming resistance.

Risk — The additional equipment creates a greater number of potential failure points in the gas delivery system, increasing the potential of a failure.

Risk — Because stage-decompression divers cannot rise above the decompression ceiling, should they miss the ascent/descent line, their risk of being carried away from the boat in a current is greater.

Risk — Stage-decompression diving also tends to result in longer in-water exposure times, greatly increasing the chance of hypothermia.

Risk — The extended exposure time also equates to increasing the odds of experiencing a problem while under water.

Bottom Line

Stage-decompression diving requires training and experience beyond the norm. The only way to truly learn to properly execute stage-decompression dives is to seek out a quality training program from an experienced, knowledgeable instructor. While there are increased risks involved, done properly the risks of stage-decompression diving are manageable within an acceptable level.

Technical Training Agencies

IANTD (International Association of Nitrox and Technical Divers) reorganized in 1992 to expand from basic nitrox training. Offers full curriculum of tech courses, instructor programs and insurance.

ANDI American Nitrox Divers International. Ed Betts and Dick Rutkowski joined together in 1988 to form American Nitrox Divers, Inc. (“ANDI”). The purpose was to standardize Instructor Training, Sport Diver Training, and refill station dispensing procedures for Enriched Air Nitrox diving.

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Neptune Dive Center and Fairtex Sport Club and Resort. 179/208, moo 5, North Pattaya Road, Pattaya (Naklua), 20150, Chonburi, Thailand.

Tel: 038-371141 Fax: 038-371446

Mobile: English, Nederlands, Deutsch. 086-1532636

Mobile: Thai 081-1509562

Email: info@diveneptune.com   scuba@tttmaxnet.com  

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