DCI in Thailand

[String]

Multi day repetitive dives has been shown to increase the risk of DCI. (Don't have the reference handy and I don't know if there is newer research in this topic)

I cant remember the exact source but a 2005 study agreed with that showing that there was an increased risk of DCS for divers well within the tables caused by multiple day multiple dive profiles. Various theories such as cumulative effect from a body not totally off gassed, microbubbles and so on.

Common sense would hint nitrox may help here but there isnt any evidence to support that despite people looking. The other issue is people skirting 1 min NDL on air, then skirting 1 min EAN32 NDL are exposing themselves to the same risk so its not safer. Using nitrox on air tables would be expected to reduce the risk but again, its not safer according to research (due to the already very very low % of DCS masking any benefit).

 

[String]

It is true that diving techniques change over time, but it is not always for the best. The techniques and theeories have changed, but my impression is that this has led to an increase of decompression-related accidents such as the one documented in this thread.

Again there is no documentary evidence to support that claim (and not in the paper you quoted when i pulled it off medline). Yes you would EXPECT to see far far more cases of DCS today than 20 years ago - there are near 100 times as many dives taking place. There is an increase however its actually lower than you'd expect simply multiplying out the numbers to factor in the increase in dive numbers. That would hint the opposite from what you claim - its actually safer today than it was 20 years ago so modern methods are actually doing a better job DESPITE poorer training.

The fact is that without dive

computers, some of the dive profiles (including the one in this thread) would not be possible.

Thats a fairly meaningless comment, a dive with 2 mins spent at 30m and 35 spent at 10 meters is NOT the same dive as 37 minutes spent at 10 meters. Totally different on gassing, off gassing and other conditions. You just cant compare the things. The fact is the old style tables made it impossible through their own limitations to plan specific dives at all and failed to plan even more safely. The older tables had severe limitations.

For example the navy tables (i) had a higher acceptible DCI risk per dive due to on site chambers (ii) based on a fitter population baseline (iii) avoided much repeated diving. This is common with a lot of older tables. There are very good reasons that for decompression diving these days far newer techniques are used such as gradient factors on buhlmann and newer algorithms such as VPM. The main reason being the older methods (even AS square profile) were tried and found to be unacceptable dangerous regarding DCS risk.

There is a whole industry that has grown up which is geared toward this technical diving, and has a vested interest in maintaining that the newer techniques are an "improvement."

Mainly the industry develops new techniques and methods as the old techniques have been found to be dangerous. See my example above with tables. 20 years ago nitrox was unheard of, deep air was common and so on. All of these were a bad idea then and lunacy in the modern day where better choices are available. Yes lots of people DID deep air on the old tables. Lots of them got bent and/or died. Far more than they do today.

The reason is that while the computers won't vary in their analysis of a given dive profile (unless changed by the diver), the diver's own physiology will vary, and suseptabilities wall also vary.

That is no different to tables of any sort. Every human is different with different risk factors. Fudge factors for tables were taught just as computers (including stinger) have compensation modes to do the same thing. Just like tables computers work on a statistical model - they dont know the individual concerned so its up to the diver to set his own level of conservatism.

Divers need to be aware of this, and treat the dives and their computers in a very respectful way in order not to have an unscheduled trip to the recompression chamber.

No more than they do with tables. Assume a square profile dive. Cutting to within 1 min NDL left on a computer and a table associates EXACTLY the same risk assuming the same algorithm used in both. Thats the only like-for-like comparison possible. You cant apply multi level computer to square profile table in the same way as they are different dives.

 

[John C. Ratliff]

String,

I think if you'll look at the paper again, you'll see that they are very concerned that the percentage of type 1 to type 2 decompression illness has changed from previous times:

Change of occurance of type 1 and type 2 decompression sickness of divers treated at the Croatian Naval Medical Institute in the period from 1967 to 2000.

Andric D, Petri NM, Stipancevic H, Petri LV, Kovacevic H.

The Naval Medical Institute, Department of Undersea and Hyperbaric Medicine, Split, Croatia.

A significant change of occurrence (p=0.0343) of type 1 and type 2 decompression sickness (DCS) of divers in Croatia was observed in the period from 1991 to 2002 (type 1: n=26, 37.68% and type 2: n=43, 62.32%) compared with the period from 1967 to 1990 (type 1: n=93, 52.84% and type 2: n=83, 47.16%). The change was attributed to the extensive usage of diving computers and artificial gas mixtures which enable extended bottom times and deeper dives, thus putting divers at an increased decompression risk.

While the rate is not know, the "hits" they are receiving are worse now than in the comparison time period cited (1967 to 1990), and they attribute that to mixed gas diving and the use of computers. These are not my words, but theirs. And this comparison is valid. Those who are getting a decompression sickness "hit" are being hurt worse, at least in Croatia, today than in the past.

SeaRat

 

[MoonWrasse]

I cant remember the exact source but a 2005 study agreed with that showing that there was an increased risk of DCS for divers well within the tables caused by multiple day multiple dive profiles. Various theories such as cumulative effect from a body not totally off gassed, microbubbles and so on.

Common sense would hint nitrox may help here but there isnt any evidence to support that despite people looking. The other issue is people skirting 1 min NDL on air, then skirting 1 min EAN32 NDL are exposing themselves to the same risk so its not safer. Using nitrox on air tables would be expected to reduce the risk but again, its not safer according to research (due to the already very very low % of DCS masking any benefit).

Although I do multi dives over multiple days over a period of 3 weeks or so in Phuket, where the OP had his accident, I don't dive for more than 3-4 days before taking an off day.
In his case, if I read correctly the accident occured on day 2 of a multi day /multi dive per day trip.

My dives can be deeper (for sure the first 1-2 of the day), but I don't use a 15L tank, thus my bottom times are often limited by air. His accident has however caused me to rethink about upping to a 15L tank. I also don't dive to the NDL edge, however I understand the lure of those sirens.

One idea is during a multiday/multidive trip, is to up the personal adjustment on subsequent days. Also I've starting logging no-fly time provided just after a dive, to monitor no-fly creep, which I've noticed on my last trip starts to exceed 24 hours by my last day. That is a reminder of how much residual N one has accumulated.

 

[String]

While the rate is not know, the "hits" they are receiving are worse now than in the comparison time period cited (1967 to 1990), and they attribute that to mixed gas diving and the use of computers. These are not my words, but theirs. And this comparison is valid. Those who are getting a decompression sickness "hit" are being hurt worse, at least in Croatia, today than in the past.

SeaRat

Again those disagree with research by the navy DDRC, DAN and others who are seeing a % total decrease in all forms of DCS. The statements also contrdict themselves mentionining using rich mixes to extend bottom time then mentionining "increased risk of decompression". Its a very muddled statement. More people are diving deeper these days thanks to mixed gases and advances in decompression models making it far safer for them to do before. That said - a bend on helium is much worse than a EANx bend to treat.

 

[String]

Ive just plotted (or rather tried) to plot those dives using my '88 tables (which although are still official are generally regarded as unsafe today especially for deeper dives. The result? Those profiles are too aggressive to even begin.

Firstly, the 12hrs SI from previous day has a big effect, this means you start on a different tissue code to an unsaturated diver.

Assuming atmospheric pressure > 984mb and sea level, plotting those average depths (so not 100% accurate but near enough):

D1 - Would have had a mandatory 1 min deco stop at 6m. Close to the line
D2 - Starting on code C. Unplottable, so far off tables (so over 21 minutes of stops)
D3 - Off tables, 15 mins stops minimum
D4 - Off tables > 6 mins stops

So from there dive 1 would have had a mandatory decompression stop with the other dives each requiring over 20 mins of stops due to short SI. All in all, nasty.

Even assuming no previous day diving, the first dive was doable (coming out on code E on these tables) but the second dive would require deco and the others unplottable.


Assuming a square profile maximum depth ALL the dives are unplottable (so requiring > 21 mins of stops).

---

Im trying to plot them on the Suunto dive manager planner but as its seemingly the worst piece of planning software ever created ive managed to crash the program twice and lose data twice so may take a while. I'll see what V-planner thinks later.


Given these dives were apparently on air that 1 day profile is way too aggressive for me personally, assuming the previous days diving was similar id be very happy attempting to come near it.

 

[John C. Ratliff]

String and others,

The reason I got to reading this thread is that I wanted to know more about dive computers and how they work. I've been diving for many, many years (since 1959), and have used the tables (NAUI, first their 1981 and then their 1990 tables) for my diving. I do a lot of vintage diving (with double hose regulators), but am also working on new diving concepts (concerning swimming underwater). I wanted to get into the computer age and get a good, conservative diving computer. I work for a semiconductor manufacturing company, and wanted the benifits of my work for my diving. I also needed to replace a Seiko Dive Watch that had stopped functioning about five years ago. I did have a Pirmtron dive watch that I couldn't kill (it's been to 90 feet) but with the numbers worn off the bazel, and a Timex Ironman watch I found in 22 feet of water in the Clackamas River, and figured if it was good for 22 feet, I'd dive it in the river.

But I needed a good replacement for these, as it looked pretty funky even to me (and yes, that is a word). I was torn between the Suunto Mosquito and the Suunto Cobra, as I am also a free diver, but my work on swim fins needs the air integration of the Cobra. I ended up selecting the Mosquito as a compromise. But then, my son presented me with a brand new Seiko Dive Watch for Christmas, so I took the Mosquito back to the LDS and for a bit more, got the Cobra (my wife's Christmas present to me).

The last week or so I've been playing around with it, and also wanted to know the difference between diving with the Cobra and diving using tables. As String indicated, there is a world of difference, and many possibilities open up that are not there with tables. The biggest is the real-time monitoring of my dive profile. But this is not so much to give me extra bottom time, as to document the dive more accurately, and make staying within no-decompression limits easier.

The problem this incident presented to a former tables diver has helped a lot in my understanding of both the advantages and limitations of dive computers. String, thank you for challenging me on what I have said here, as it helps to keep a person "on his toes" to go through the explainations of why I made certain assumptions about the dive profiles I analyzed.

TaipeiDiver, thanks for putting up the scenario that you suffered through, and for letting us look at it. It has helped us all understand better how to dive in the future. It would be very interesting to see the actual profiles if you can ever get them downloaded. I certainly appreciate your candidness in presenting the situation, and letting us discuss it. I do a lot of accident and incident investigations in my work as a Safety Engineer, and the purpose is not to point fingers, but to learn and prevent future incidents from occurring. NAUI's philosophy was "Safety through Edacation," and this is a part of the education process. Thank you for letting us have a go at it.

SeaRat

 

[String]

Ive plotted similar dives not on suunto dive manager and even that is distinctly unhappy. Assuming NO loading from the previous day you end up with 16 mins NDL - if there were similar dives the previous day that would be almost zero. Follow up dives get lower and lower until they run into mandatory stop territory.

Did you download these dive profiles to a computer and if so any chance we can see them as a screen shot ? Everything ive looked on so far including suuntos own simulator have these as very aggressive profiles.

 

[Willie]

If I were doing dives to that depth (around 90ft), I would have added a 3-5 minute deep stop at half maximum depth, say 45 ft. (You may have done this in your multi level, but it wasn't mentioned.) According to DAN this type of stop is very effective in reducing bubbles in the body when the diver reaches the surface.

Great post and discussion. Thanks to all who have participated.

I had previously read this DAN article

https://www.diversalertnetwork.org/news/article.asp?newsid=514​

and found it very informative and it certainly makes sense to me. I planned these mid stops into the few deeper profiles I have done.

Here are a few excerpts. I highly recommend the entire article.

... the introduction of an additional deep stop ... reduced the previously recorded 30.5 percent incidence of high-grade bubbles to zero.​

NAUI has now suggested that a deep stop might well be incorporated in recreational diving by taking a one-minute stop at half the depth and followed by a two-minute safety stop at the 15- to 20-foor level instead of the three minutes currently recommended.​

The secret of the deep stop rests in the paradigm shift of "beating the bubble" versus "treating the bubble." The former utilizes the deep stop to ensure that the fast tissue critical gas supersaturation is not exceeded and stops bubbles from forming in the first place. The long ascent to the 20-foot stop, as is currently done, involves "treating the bubble"; we know this produces 30 percent asymptomatic or so-called "silent bubbles" on the surface, which may be indicators of decompression stress or even potential DCS.​

 

[MoonWrasse]

Some other snippets of note from the above linked DAN article:

The incidence of DCI as reported annually in the DAN America Report on Decompression Illness, Diving Fatalities and Project Dive Exploration shows an average of these types of DCI:

* 25 percent decompression sickness (DCS) Type I (pain or rash only);
* 64.95 percent DCS Type II (neurological); and
* 9.8 percent AGE (arterial gas embolism).

Thus for recreational scuba divers, most injuries are primarily neurological rather than pain-only. Additionally, they probably originate from the brain or spinal cord rather than from the connective tissue of the joints.

and

What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate.

BTW the OP's case sounds like type 1.