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It seems my reply to Christina Young on 3/29/95 has caused "someone" a bit of concern. Someone, who shall go unnamed, forwarded my comments on to another person, asking for his comments. That person then forwarded his comments on to yet another individual asking for his thoughts. He then forwarded it on to me asking for an elaboration on my original commentary. So it would appear that my message has followed a rather circuitous route in coming back to me. Rather than letting this issue just fad away into private E-Mail, I will reopen it to a broader discussion. Restating Christina Young's original scenario.. >1. You're on a deep dive in cold water. >2. You're wearing your drysuit with normal drysuit underwear. >3. you have incurred a significant decompression obligation, >4. you accidently rip your suit and it floods. >5. You immediately abort the dive, but still must do your decompression. >6. On the deco line you start to become very cold, and due to the cold, your off-gassing efficiency is significantly reduced. Christina gives us a very real-life scenario, one that I am certain has occurred in the past, and will no doubt occur again in the future. Most of the replies posted were on ways to avoid the situation in the first place, which all things considered is the best approach. But, given the above scenario, what "Should/Could" the diver in this situation do?? Christina continues on to ask 2 specific questions, and offer one comment. >A. How can you tell the point at which off-gassing efficiency on the deco line falls below the off-gassing efficiency that would exist if you were in the dry, warm cabin on the boat breathing 100% O2? >B. Can you tell? Is there a mathematical temperature model that would tie into whatever deco algorithm you're using that you could use to determine this (or the optimal deco profile under your circumstances)? >C. I suppose that this is a highly individualistic thing, but perhaps generalizations could be made? To this I replied... ================ Now your question is whether it is better to chance a missed deco and go for surface deco on 100% O2, or sit in the water and freeze. I would say that this is going to be Highly dependent on the deco stop that you are aborting from. Obviously, the deeper you are upon aborting, and the longer you have been down, the greater the overpressure differential upon surfacing is going to be, and your chance of getting DCS. If it was more than 3 stops from the surface (30ft/10m) I would strongly consider surfacing, re-suiting, and inwater recompression. If you are 2 stops (20ft.6m) it gets muddy. If you are 1 stop (10ft/3m) you could probably get away with it. Last week we spent quite a bit of time working out a surface decompression routine for Abyss to be used by commercial divers. The gist of it is that a diver can ascend from 40ft, regardless of deco obligation, to the surface. We allow him 5 minutes (MAX, 3 min is much better) to get out of his gear, and get into a surface recompression chamber. We then blow him back down to his last depth + a factor, and then decompress him back to the surface as though he were making an altitude dive (surface pressure < 14.7psi). Did this help at all, or did I just add more confusion?? =================== Clearly I seem to have added to the level of confusion. 1st foremost, I still stand by what I said. What the diver does in the above situation is HIGHLY dependent his current situation. How deep he was, how long he was there, the bottom mix, his current state of decompression, and his remaining deco obligation. With regards to the Surface Deco comments I made, some elaboration is required. SurD is a common practice among commercial divers the world over. The manner in which it is performed does vary however. DCIEM requires that the diver decompress to 30ft in the water prior to ascending to the surface chamber. The Brits tend to take their divers to the surface from much deeper depths. With Abyss we will be using a depth of 30-40ft prior to ascent. This is NOT intended for us in saturation diving, but only in relatively short excursions. DCIEM allows for 7 minutes of surface time prior to recompression. Abyss will be set up for 5 mins, with a reccomendation for as short an interval as is possible. When the diver enters the recompression chamber he is then taken back down to his last depth, plus an additional factor based on the overall profile of his last dive. He is then decompressed on a schedule that is similar to making altitude dive, where he would be decompressed to allow an exposure to an atmospheric pressure of Less than 14.7psi. That said.. So, for the sake of argument, lets create a hypothetical dive to use as a basis of comparison. (for this simulation, I am using the Abyss-150, 50% asymmetrical, Deep/Mix, 32 compartment algorithm) Scenario #1, Dive to 200ft, on Air, for 20mins of true bottom time. Deco on Air to surface. Depth Rate Time Total Gas & Percent CNS END ppo2 ppo2 OTU OTU Status (ft) (ft/min) at time (ft) arrive depart arrive depart 0 150 0.1 0.00 O21%, N79% 0.00 0 0.21 0.21 0.00 0.00 Surface 200 75 20.0 21.33 O21%, N79% 16.95 200 1.48 1.48 0.12 35.73 Entered by user. 50 75 2.0 25.33 O21%, N79% 17.70 50 0.53 0.53 37.85 38.07 DECO 40 75 5.0 30.47 O21%, N79% 17.70 40 0.46 0.46 38.08 38.08 DECO 30 75 8.0 38.60 O21%, N79% 17.70 30 0.40 0.40 38.08 38.08 DECO 20 75 12.0 50.73 O21%, N79% 17.70 20 0.34 0.34 38.08 38.08 DECO 10 75 33.0 83.87 O21%, N79% 17.70 10 0.27 0.27 38.08 38.08 DECO 0 20 0.3 84.25 O21%, N79% 17.70 0 0.21 0.21 38.08 38.08 Surface #1, is the actual planned dive. Diver has a deco obligation of 62.92 minutes. Lets say that the suit is torn at the 30ft stop, but the diver is able to complete that stop. Upon reaching 20ft, the diver has a Pigt for compartments 4,5,6 of 3.00bar. At that instant, those 3 compartments are the controlling compartments for decompression obligation. If an ascent directly to the surface is now made, the diver will arrive with a apx 3bar overpressure. Following normal deco, the diver would arrive with a 1.7bar overpressure in controlling compartments 8-12. This leaves our diver with a 1.3bar differential, and that is NOT an unsubstantial amount. Chances are good, this diver would take a hit. To make things worse, the diver arrives cold, and will probably desire to get warm. Warming up on deck "May" only serve to exacerbate an already bad situation. Being warm during deco while under pressure is good. The use of a warm water suit during deco could be highly advantageous. However, upon surfacing the last thing you want to do is to "significantly" heat yourself. Certainly the diver needs to get back to a normal/comfortable temp, but should not be "Heated". Without the additional pressure gradient of depth, the increased warmth could lead to excessive gas coming out of solution, and presto, you get a post dive hit. So, our diver aborts his Deco at 20ft and surfaces. he now has 3 viable options. 1. Go on 100% O2 and pray. 2. Go on 100% O2 and call for medivac if you are near a chamber. 3. Go back in the water for In-Water Re-Compression. (Richard Pyle., feel free to jump in ) 4. Go back in the water for Temp In-Water re-compression awaiting the arrival of transport. All 3 options assume that you have a good supply of O2 available, #3 requires even more. If a diver is making this kind of a dive, and does NOT have a supply of O2, he deserves what befalls him. Options 1 & 2 are No-Brainers, and only require that the diver sits tight and waits........ Options 3 & 4 raise an entirely different set of possibilities. Now, my opinion. If it were me, I would go for the In-Water Recompression route. Even if suitable transportation to a chamber could be had within a relatively short period of time. The time spent waiting for that transportation is better spent under pressure, so long as 1. the required equipment is available. 2. the diver is in good enough condition to safely perform the operation. 3. The dive environment allows for this to be done. Remember, to "Safely" perform IWR you must have. a. A full face mask b. sufficient supply of O2 c. adequate thermal protection d. an attendant to be with the diver at all times e. weighted rope or a weighted seat for the diver f. some form of communication from the diver to the attendant and to the surface. Now, lets open this up to some real discussion. What would YOU do??????????? /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ Christopher M. Parrett, President, Abysmal Diving Inc. 6595 Odell Place, Suite G. Boulder Colorado, USA 80301 Ph.303-530-7248, fx 303-530-2808 Makers of ABYSS, Advanced Dive Planning Software. Available in English, French, German, Italian, Portuguese and Swedish. Abyss, Mixed Gas, Technical Nitrox, Recreational Air. Abyss, Technical Logbooks featuring 22 integrated databases.
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