21 April 2010


Recreational divers are taught to fear decompression. It is described as something dangerous, something that will very likely result in injury. If you are not properly trained, equipped, or experienced it is, indeed, dangerous. Technical divers, however, routinely carry out decompression dives without incident. My instructor, for example, has been a leading technical diver for decades and he has never gotten the bends.

IANTD is probably the mostly highly regarded technical diver certification agency.

"Decompression" is the point at which your body has absorbed an amount of inert gas (nitrogen, helium, or both depending on the mixture you are breathing), great enough to prevent a direct ascent to the surface. As you breathe gases under pressure (i.e. at depth), your body absorbs more and more of the inert components into tissues. When you ascend, those inert gasses comes back out of your tissues and are released as you exhale. There is a point at which your tissues become so deeply saturated that, if you were to ascend to the surface directly, too much gas would come out of solution too quickly. Your body wouldn't be able to release it fast enough (like opening a shaken soda bottle). If this happens, bubbles form and you get "the bends." When your body reaches this level of saturation, you are said to be "in decompression" (or in "deco" for short). Being in decompression is completely harmless, so long as you ascend slowly enough to release built up inert gas. To achieve this, a diver who is in deco, must carry out decompression stops. Periodically, on the ascent, the diver must stop below a certain critical point (calculated in advance of the dive) to allow time for gas to be released.

Typical Technical Setup

Obviously, this can present serious problems for a diver that is unprepared. If, for example, you do not have enough breathing gas to perform the necessary stops, you will be faced with either drowning or ascending too quickly, omitting the stops and likely getting bent. Minor bends cause pain in the joints. Major bends cause embolisms, paralysis, and death. The severity of the injury is related to the severity of the violation.

My personal opinion is that decompression diving should not be taken lightly. I believe the decision to enter deco should never be made while underwater (something a few people I have dived with sometimes do). I believe the dive should be planned in advance and all divers in the group should be prepared to handle it. Before this course I had entered deco very briefly on a handful of occasions. In two instances it was because people with whom I was diving chose to remain at depth longer than planned (something I'm still angry about). The other times I planned the dives so that I could familiarize myself with the procedures and with my dive computer's functionality (so that I would be prepared for times when unplanned decompression occurred). In my tech course, I'm learning to undertake significant decompression.

Some people wonder why I would want to do this. Why accept greater risk while diving? Well, there is a lot to see and do underwater that can't be seen or done without decompression diving. But most of all, decompression diving is not that much different from a dive without decompression (i.e. a shallow or short dive). If being in decompression means a diver cannot make a direct ascent to the surface: EVERY DIVE IS A DECOMPRESSION DIVE. Even the simplest dive to 10m has a decompression obligation of 1 minute (due to mandatory slow ascent rates). A dive to 5m has an obligation of 30 seconds. Ascents must be slow even on shallow dives.

Recreational divers can dive to 40 meters and ascend to the surface in as little as 4 minutes (more typically 7 minutes). Already, this is a significant obligation (it is highly unlikely a diver could ascend safely to the surface from that depth in the event of equipment failure or an out-of-air situation). So why do people view this differently than a "true" deco dive with a 20 minute decompression obligation? It isn't! The only difference is that the technical diver preforming the "true" decompression dive has more redundancy in his or her equipment, better knowledge of how to safely carry it out, and greater skill and control underwater. In my opinion, it is far safer to dive with a good technical diver (even in decompression) than it is to dive with a novice (or even somewhat experienced) recreational diver.

The point I'm trying to make in all of this is that becoming a technical diver is not all that crazy. Nor is it an acceptance of undue risk. If nothing else, it is development of important skills and methods to keep me safe in routine recreational diving settings.

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