Just how often does "undeserved" DCS occur?

[chepar]

I have read and heard that no matter how careful a diver is, sometimes DCS can just happen, hence being termed "undeserved" DCS.

My question is, how often does this happen? Is it a rare thing - maybe falling into the "fluke" category, or does it happen enough that I should be overly concerned each time I dive? (This is going with the assumption that I am being as careful as I can be and not engaging in any activities that would lead me to be more prone to DCS in the first place).

If you haven't had a case of undeserved DCS before - how many dives have you done?

 

[Arduous]

Hi chepar:

Decompression theory is just that …THEORY. It is based on science, but it is not an exacting science. Through many years of experimentation, tables and or algorithms have been developed to give the diver the highest probability of a DCS free dive. However all the factor that lead up to a DCS incident are not known. We understand the need to be well rested, physically fit, alcohol & drug free and well hydrated. We understand the importance of a slow controlled accent and diving with in the ( Theoretically ) established limits of Nitrogen and Oxygen exposure for the recreational diver. But we are all physiologically different and individually we differ from day to day, dive to dive. The dive profile that we have been diving on with out incident for the last several week could for reasons that we may not be able to explain, give us DCS hit. We just don’t have all the answers yet. When diving recreationally, dive well with in your abilities and with in the established recreational limits. Be fit rested and hydrated and stay off the booze and drugs. Follow the safe diving practices of moderate depths and slow accents and in THEORY you should be ok. Dive Safe ………………..Arduous

 

[Liquid]

From my experience it goes something like this-We instructors alwaise teach that DCS can sometimes happen, with no apperant reason. We teach it, amongst other reasons, to cover our arses in case something goes wrong and a student gets DCS when he think he shouldn't have. It also adds a "Fear" factor, that will make students act more cotiously in their future diving career.

BUT-I know some people that had DCS. Some admitted that it was their own fault, a lot didn't. But when I questioned those who claimed "undeserved" DCS I found out it wasn't undeserved, unless it was a very fat (usualy also quite old) person, that although didn't dive out of the table limt, kept himself quite on the edge. DCS dosen't ocure becouse it wants to, it happens due to certain things that affect the chance to have it. Keep yourself well within the conservative side of the tables, do not do anything that may increase the chance of DCS (drinking alcohol, not drinking water,not eating well, etc.,etc...), and you'r completly safe from DCS. Almost .

As for amout of it happens-Like I said, I have never saw a case of DCS that was completly "undeserved". These things are very rare, and tend not to be so "undeserved" as people describe them.

Oh-The best way to avoid DCS is quite simple- stay dry.

 

[Lost Yooper]

I agree with Liquid. In all likelihood, there's always a reason for DCS. I'd be willing to bet that 99.9% of all incidences of DCS are the result of human error or ignorance of proper deco procedures, pre-dive preparation, and/or post dive activities (also human error). However, there are a few preconditions that can exist (like a PFO) that can increase the chances of DCS and be totally unknown to a diver.

Mike

 

[DocVikingo]

Hey, Liquid, as a fat, older diver who sometimes presses the edge, I feel compelled to respond here.

Seriously, chepar, this subject is worth spending some time on. As words are always important, let's start with terminology. The use of terms like "undeserved" DCS (and I know you did not coin this) at least implies the existence of "deserved" DCS, and can carry a certain moral weight in the minds of some people.

While much is known about what causes DCS, much remains to be uncovered. It therefore seems unsupportable to apply such terms until the field has a full understanding of when DCS is to be expected. Furthermore, even given a complete ability to predict instances of DCS, the use of possibly disparaging terms can make the diver feel guilty. It can perhaps contribute to the well-known phenomena of denial of DCS with attendant delay of treatment & probable additional harm.

In an attempt to circumvent this, some major dive organizations have adopted the use of less judgmental terms. DAN, for example, now uses the term "unexpected" DCS, which I rather like.

Moving on to your question, upon investigation the majority of cases that I have seen/heard of did involve one or more of the factors known or believed to be influential in causing DCS. These included risky dive profiles like pushing the NDL envelope, missed deco obligations & safety stops, and rapid/uncontrolled ascents. Individual risk factors also played a role. Common were such things as poor physical conditioning, overweight, advancing age, predisposing physical conditions (e.g., PFO), current illness/injury, dehydration, fatigue, becoming chilled or other stressors during the dive, use of alcohol & legal/illegal drugs, and vigorous exercise immediately before or after diving. In a small number of cases, no factor or factors known or suspected to be involved in DCS could be identified.

Based on the dive science to date, your opening remark that, "I have read and heard that no matter how careful a diver is, sometimes DCS can just happen...." does in fact seem to be true. However, you may find it reassuring that by carefully following all dive profile rules & safety guidelines your chances of sustaining DCS during recreational diving are very, very small.

Good topic.

DocVikingo

 

[Liquid]

The matter of "undeserved" DCS, or as DocVikingo offered, "Unexpected" DCS (which in my opinion is much better) is a very seriouse one.

Dcs is a thing that is coused by several factors, some of them are not known well yet, though most are known enough to allow a relatively very safe DCS scuba dive. Nothing is 100% certain. It's kind of like the atomic model of of Hydrogen (I reffer to the one suggested by Shrodinger, or whatever his name spells like), where the darker areas mean you have a greater chance to find the neutron and the brighter a lower chance, yet you never know exactly where. Same goes with DCS, there isn't a point where you can say "cross it and you have DCS, avoid it and you won't".

As an instructor I teach my students about Unexpected DCS mainly to fright them a bit, and make them think about diving in a more conservative way. Like I said before, I don't belive in it. All the cases of "Unexpected" DCS I observed, where aventualy not some. Ofcourse, people are not alwais aware of the factors that contribute to the chance of having DCS, and many times people are ashamed of admitting it. When diving close to the edge, you take a risk. You have to calculate your risk every time you go to dive.

To sum it, though I will never promise anything to anyone about it (I have to cover my ass, you know ), I can tell that if you dive conservative, and do not push the limits, the chances that you will have DCS, even if you are elderly, everwheighted and completly out of shape (as one of the best instructors i know is+ he is also very ugly) are VERY VERY low. Safer than crossing the road, or, as rescent studys showed, even safer than playing Bowling .

 

[Dr Deco]

Dear readers:

One aspect of dive tables that is not well known is that there are not, in physical reality, any “table limits.” While table limits might exist at the gaming tables of Las Vegas, they are not a physical limit. True limits are the speed of light and the “sound barrier” but not bend-no bend limits. This concept, while mentioned often, is a hold over from the Haldanian theory days. While this theory is commonly held, it is not correct. "Table limits" leads to the idea that within a certain range, you will never get DCS and beyond you surely will. The “underserved hit” makes its appearance under these circumstances.

The Haldane tables were based upon the concept of limited supersaturation and the metastable limit. This idea embodied the principle that a liquid could hold a given quantity of dissolved liquid or gas and that, if below the limit, the solution would stay supersaturated forever. This concept was originally investigated in detail by the German chemist Wilhelm Ostwald who concluded that saturation was only possible if there were no impurities in the solution at all.

We know (and have known since the first half of the 20th century) that liquids contain minute gas bubbles that function as micronuclei. These are primarily generated by movement (kinetic activity). The process is termed hydrodynamic cavitation.

When saturation is exceeded, these will grow unless hindered by surface tension. Physical activity (and hydration, and individual biology) will vary these parameters in such a way that a cluster of micronuclei could grow and DCS result.

The best way to avoid getting a hit is to avoid strenuous physical activity during the gas uptake phase (bottom time) and to avoid similar activity when topside. Some activity will help with blood flow and off gassing. Stay within the tables, of course. The whole process is a biophysical one and “underserved” is a misnomer from history. This is not necessarily to imply culpability and bad technique, just to indicate that things do have a reason on this planet. We are not at the whim of a capricious god.

The whole business is complicated and for this reason I have my decompression physiology class.

Dr Deco
:doctor:


Advanced Decompression Phsiology, June 22-23, 2002
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Liquid]

Just a thing I thought about-

Doc- have you ever heard of a case of "undesrved" DCS ever to happen to a young, in good shape person, with no fly after the dive, no alcohol before the dive, that drank enough water, didnt do anithing like"strenuous physical activity" after dive, after a dive of 30 minuets to 10 meters?

If the answer to that is yes, than I will start belive in "undeserved" DCS .

 

[Dr Deco]

Dear liquid:

In the situation that you described, no I have not. I do not subscribe to undeserved hits either.:teach:

Biophysically, the reason would be that the supersaturation encountered in such a dive would require micronuclei that were too large. In addition, one would need quite a few of them. These situations do not occur in nature.

Dr Deco
:doctor:

 

[scubabunny]

About 2 years ago, there was a student at our shop. He was military, in very good shape, and took diving very seriously. He went through open water with no problem, and from what his instructor said he wasn't a "testosterone" diver looking to push his limits. On his 3rd dive after getting certified, he ended up taking a chamber ride. His dive profile was well within the limits...his computer was downloaded and max depth was around 50ft, slow ascent, with a safety stop.

Now granted, I got all the info second hand (or third hand I guess) from his OW instructor. But, apparently the doc at the chamber said the diver's genetic makeup made him prone to DCS, so he shouldn't dive anymore. Is this possible? Can some people be more susceptible while still being in good physical shape?