DCI in Thailand

[Jamdiver]

So sad to hear, glad that you've made a full recovery though.

Brings to my mind the words of a former instructor, "Everyone has a bubble out there with their name on it."

 

[Batfish]

The chamber operator was a big league of gentlemen fan

Was he a local? Did he let you touch the precious things?

 

[Taipeidiver]

Was he a local? Did he let you touch the precious things?

It was a local chamber, for local people...

 

[John C. Ratliff]

I'm glad to hear that your going to make a full recovery. As I'm sure others will ask you, would you mind sharing with us the profile of your 4 dives (depth and bottom time). Also what safety stops did you do (time and depth) ?

All dives were on air, using a single 15L steel tank.

Dive 1 - 0733hrs, 28.0 metres, 61 minutes (multi-level dive), following a surface interval of 12 hours, 13 minutes. 3 minute safety stop at 5 metres.

Dive 2 - 1031hrs, 27.4 metres, 54 minutes (multi-level dive), following a surface interval of 1 hour, 56 minutes. 3 minute safety stop at 5 metres.

Dive 3 - 1331hrs, 24.3 metres, 41 minutes (multi-level dive), following a surface interval of 2 hours, 5 minutes. 3 minute safety stop at 5 metres.

Dive 4 - 1704hrs, 28.0 metres, 49 minutes (multi-level dive), following a surface interval of 2 hours, 52 minutes. 3 minute safety stop at 5 metres.

Okay, I've looked at this with my old tables, and have come to the conclusion that, had you been using tables instead of your computer, you would have seen a problem developing. I could not calculate the second dive as a planned dive using the NAUI 1990 tables, or the NOAA tables. The NAUI 1981 tables would allow the second dive, but you would have been way into decompression diving even on the first dive. Let me explain.

When using tables, you make certain assumptions about the dive. Your time starts from when you leave the surface, to when you begin your ascent to end the dive. Your depth is the maximum depth of the dive, in this case that was 28 meters (90 feet on the NOAA No-Decompression Air Tables, 100 feet on the NAUI 1991 tables; we'll use the NOAA tables here for the depth conversion; technically 28 meters is 91.86 feet, which should count as a 100 foot dive, but we'll let that slide). You started out without any Residual Nitrogen Time (RDT), and had an Actual Dive Time (ADT) of 60 minutes (and that's giving you a bit because if it's over 60 minutes at 61 minutes, it should be counted as 70 minutes, but the NAUI Dive Tables tables won't compute that dive). You stopped at 5 meters for 3 minutes, but the old NAUI tables say you should have stopped at 10 feet for 25 minutes for this dive profile. Your Group Letter is "M" for this dive.

You spent 1:56 on the surface, which reduces your Group Letter to "H". You plan a dive for 27.4 meters (89.9 feet), which is 90 feet on the NAUI tables (both 1981 & 1990). If you look at your second dive to 90 feet, on the NAUI 1981 tables, you have 33 minutes of RNT. If you then plan a dive for 54 minutes, you must add that 33 minutes of RNT to the 54 minutes of ADT, which equals 87 minutes Total Nitrogen Time (TNT). Ninty feet for 87 minutes is not even on the chart for the NAUI 1990, NAUI 1981 or NOAA dive tables as this is a decompression dive. According to the US Navy Standard Air Decompression Tables available in the 1980s, you would have been required to take a stop at 20 feet of 18 minutes, and a stop at 10 feet of 48 minutes. Your Repetitive Group Letter (RGL) would be "O".

With a surface interval of 2:05, your RGL would be "H". If you then decide to plan a dive to 24.3 meters (79.7 feet, 80 feet on the US Navy Dive Tables), you would have a RNT of 33 minutes. The ADT was 41 minutes which is added to the 33 minutes to give a TNT of 74 minutes. A dive to 80 feet for 80 minutes requires a decompression of 7 minutes at 20 feet, and 37 minutes at 10 feet. Your RGL is now "N".

The last dive is then planned. You have a surface interval of 2:52, which reduces your RGL to "F". The last dive is planned to 28 meters, or 91.9 feet. This is a 100 foot dive on the tables. Your RNT is now 22 minutes. You plan your last dive for a dive time of 49 minutes, which when you add the 22 minutes of RNT, you have 71 minutes TNT. A 100 foot dive for 80 minutes requires a stop of 23 minutes at 20 feet and 48 minutes at 10 feet. When you end the day, your RGL is "O".

I realize that, with computers doing real-time analysis of the profile, this is very conservative, but this is how we computed dives up until dive computers came into existence (we would not have allowed these dive profiles, however, as we did not do, and I do not do, decompression diving). But also realize that this number quoted in a later post, the "average depths for the four dives" is meaningless for decompression computation. I dived with the USAF, and under the US Navy guidelines, and even when on scuba using varying depths, we still took the deepest depth of the dive, and used the tables as shown above. According to this ol' Coot, you were into decompression diving on your first dive. If you add up the decompression time for all of these dives, you would have been in the water much longer than you wanted to be, but you would not have gone to the recompression chamber that day. Maybe both you and I can now appreciate why the DIR folks use tables exclusively for planning their dives, as this is a much more conservative way to dive. Yes, it cuts down on what you can do, but also, yes it will help keep you from a recompression chamber.

I was using my old tables, from my library. But you can check them for today's tables at this site:

http://www.ndc.noaa.gov/dp_forms.html

I still am wondering why these charters do not have a recompression chamber on-board if they are serving divers who dive in this manner? A five hour trip to the hospital (or longer) could be a fatal wait, depending upon where the diver is "hit."

SeaRat
NAUI Instructor #2710 (retired)
Honor Student, U.S. Naval School for Underwater Swimmers, 1967

 

[MoonWrasse]

Here's my dumb question:

If his diving profiles were so risky starting with dive #2, why didn't his DC (Stinger) flag it as a problem?

Also if the DC is permitting something so risky, wouldn't we expect to see more divers who use this particular DC getting bent more often (as people follow their DC more than tables)?

 

[String]

Plotting as tables assuming a square profile will break lots of "normal" multi level dives. Whats really needed are the average depths for the NON 3 minute safety stop part of the dive and the times involved with those. Better yet, are you able to download your profiles off the Stinger and upload somewhere for people to look at? Were any of the safety factor settings on the computer enabled? How much "saw toothing" went on during the actual dives?

Reverse profile shouldnt be an issue, firstly its not huge and more importantly the research now suggests that reverse profiles make no difference what so ever to DCI risk.

People have mentioned hydration (or lack of) already, was tiredness an issue? Did you have dives the previous day or days and when did you fly (if at all) ?

Any ascent rate warning alarms at all for any of the dives?

You mention "no PFO" - have you actually had the full PFO test (which involves the injected dye and scan) ? I dont really know of anyone tested for this who hasnt been bent - it wont show up in a normal medical.

 

[String]

Here's my dumb question:

If his diving profiles were so risky starting with dive #2, why didn't his DC (Stinger) flag it as a problem?

Not really, the tables above assume a square profile and its already stated these were multi level. A dive for example to 28m for 2 mins then 30 mins at 10m would show up as huge deco on square profile tables but no stop on a multi level profile/computer as it knows the actual profile not assuming always deeper.

Without the actual profiles its impossible really to plot a proper multi level either on deco planning software or other methods.

If it wasnt already 4am i may have plotted the averages he listed on v-planner to see what it spat up as an approximation.

 

[John C. Ratliff]

Here's my dumb question:

If his diving profiles were so risky starting with dive #2, why didn't his DC (Stinger) flag it as a problem?

Also if the DC is permitting something so risky, wouldn't we expect to see more divers who use this particular DC getting bent more often (as people follow their DC more than tables)?

The DC was calculating the algorythm the way it was programmed. I was calculating it as if I were trying to dive the same profiles twenty years ago, before these devices were developed. As you can see, divers in the 1980s using dive tables were much more conservative in how we went about determining our no-decompression limits than are today's divers. Had TaipeiDiver been diving as we used to, he would not have had a trip to the recompression chamber that day.

There do seem to be more decompression sickness accidents than twenty years ago, simply from reading over these threads. There are some who say that there are only two types of divers, those who have been bent and those who will be; but I've dived since 1959 without being bent, and I'm not about to let that happen now.

Does that mean these DCs are bad? No, it simply means that we need to realize that they are real-time devices which are not factoring in some individual responses to the dive day (dehydration, exercise, and the other factors mentioned above). As a matter of fact, I got a DC (Suunto Cobra) for Christmas this year, and will be using it too. There is a lot to say for them. But again, they are simply tools that we need to understand, and modify if necessary to our individual needs and responses.

SeaRat

 

[String]

The DC was calculating the algorythm the way it was programmed. I was calculating it as if I were trying to dive the same profiles twenty years ago, before these devices were developed. As you can see, divers in the 1980s using dive tables were much more conservative in how we went about determining our no-decompression limits than are today's divers. Had TaipeiDiver been diving as we used to, he would not have had a trip to the recompression chamber that day.

True but thats just as poor as saying he wouldnt get bent if he didnt dive before. Trying to plot multilevel dives as a square profile is like comparing a car to a cow. Totally different things except they both move.

The profiles you ran being square probably bore no resemblence what so ever to the profile he dove meaning its not a good comparison.

There do seem to be more decompression sickness accidents than twenty years ago, simply from reading over these threads.

Only in that there are probably 50 to 100 times more divers than 20 years ago and the quality of training is greatly reduced meaning far higher risks from buoyancy loss and so on.

Does that mean these DCs are bad?

No. Just like 20 years ago people got bend in and outside the tables.

 

[John C. Ratliff]

True but thats just as poor as saying he wouldnt get bent if he didnt dive before. Trying to plot multilevel dives as a square profile is like comparing a car to a cow. Totally different things except they both move...The profiles you ran being square probably bore no resemblence what so ever to the profile he dove meaning its not a good comparison...

String, that's not quite the same, but I'll grant you that the two types of profiles are different. Here's what I think about this right now, that what I'm calculating is how we would have measured the same dives in two different time periods. We are into the computer age, but the computers are based upon some of the same theories as the tables were based upon. There are some differences, however. Here's a few:

--In the old days, we taught "plan your dive, and dive your plan." Therefore, for the first dive to 28m, I would have stopped the dive at 20 minutes (one away from the "knife edge" of the no-decompression limits), and headed up.

--after the first dive to 28m for 20 minutes, if I had been planning it according to my 1990 NAUI Dive Tables, and I knew that I wanted to dive to about 27m the next dive, I would know that my RNT was 16 minutes, and I had 9 minutes of no-decompression limit bottom time at that depth. My plan would be for a bottom time 9 minutes would be in order.

I would keep going until the end of the day, but this is how I would plan these dives using tables. By the way, I did compute the dives based upon the "average depths" instead of the maximum depths shown in that one post (D1=14.6 metres, D2=15.8 metres, D3=16.4 metres, D4=14.0 metres), and it showed that using the posted bottom times, the second and third dives would have required 14 minutes each of decompression at 10 feet using the U.S. Navy Dive Tables (1980s versions).

Now we have the computers, but they are still only instruments. They can handle the multi-level dives like you mentioned, but they still have limitations. My Suunto Cobra uses the Suunto Reduced Gradient Bubble Model, and it is pretty conservative. It also has "personal adjustments," and when I look at them, I see that I immediately fall inot one personal factor that shows an incleased DCI suseptibility: I am 60 years old. "...age, particularly for divers over the age of 50" is listed as a factor. Suunto's handout shows on page 3 the depth in metres, along with the personal modes and the no-decompression limits that the RGBM model uses. For 28 meters (30 meters on their table in the handout), that limit is 18 minutes in PO mode, 14 minutes in P1 mode, and 12 minutes in P2 mode. I will probably set mine at least to P1 mode, unless I am tired, getting really cold, etc., in which case it will go into P2 mode.

There is also a warning in the front of my Cobra manual:

WARNING
USE BACK-UP INSTRUMENTS! Make sure that you use back-up instruments including a depth gaupe, submersible pressure gaupe, timer or watch, and have access to decompression tables whenever diving with a dive computer.

From what I'm seeing here, this backup simply is not happening.

Concerning your analogy of the cow and the auto for the Dive Tables verses the Dive Computer, I think it a more like a car and an SUV with 4-wheel drive capability. The SUV can go off-road, just as a diver with a DC can do much of what he wants, and still figure his decompression. The car has to stick to roads, which is more like what diving the tables is like--you have to stick to the tables if you want to know your decompression limits.

SeaRat