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I ignore the first dive - in this case you have mushed the bubbles anyway. After enough time, I ignore any first dive other than as regards the oxygen exposure - that is where the risk lies. Shimell, David (shimell) wrote: > > George > > Here's another question. > > Say you do your 220' for 25 and then ascend to do a multi-level dive to say > 90' for 25. How would you calculate the deco for this? I recall you once > talked about superimposing one table on another but I had it on my list of > things to look at. > > David Shimell > Email: shimell@se*.co* <mailto:shimell@se*.co*> > Project Manager, IBM NUMA-Q, Sequent Computer Systems Limited, > Weybridge Business Park, Addlestone Road, Weybridge, Surrey, KT15 2UF, UK > registered in England and Wales under company number: 1999363, registered > office as above > > -----Original Message----- > From: kirvine@sa*.ne* [SMTP:kirvine@sa*.ne*] > Sent: Friday, December 24, 1999 12:43 PM > To: QUEST@GU*.CO* > Cc: techdiver > Subject: SAMPLE DECO DIVE - 220 FOR 25 > > Let's run through a sample dive. I will throw out the parameters and > the standeard deco on one side, and my changes and why on the other ,and > then we can discuss it. > > We can then build the dive into a longer dive, a deeper dive and we can > add more gasses and more stituations, and then the equipment to do it. > > Let's start with this and get the discussion going that way. I need all > questions, no matter how sophisticated, so we can get out the rock. > > ***PROFILE 220 FOR 25 CHANGES > ***GAS 16% OXYGEN 50% HELIUM 1.2 PPO2 > 85 AED > > REASON FOR GAS CHOICE: the more heluim, the better . It is > easier to breathe at depth, and it is easier to decompress from, > contrary to what you have been told elsewhere. The reduced narc is > obvious. I chose the 50% heliuum for this , but the more the better. The > oxygen ppo2 should be kept intentionally low. The reason is that you do > not want to unnecessarily deplete brain chemistry to pick up "perceived" > deco advantage, expescially in light of the fact that we have boosted > the helium which reduces the nitrogen damage and loading, and thus the > deco requirement. While inert gas is inert gas for purposes of this > discussion ( or said another way, the oxygen window is the oxygen > window) the reality is that helium changes the physiological factors > that are as real in deco as the straight compartment loading and > unloading factors. Very important to us in our diving, and more so as > the dives get more severe or repetitive. We also do not want to burn the > shit out of our lungs with high PPO2's either, and keep in mind that > depending on the bottom time, we are going to be forced to expose > ourselves ot elevated oxygen to decompress. > > It is critical in multiday exposure that you reduce the oxygen dose, and > we will show how to do that in each decompression. > > STANDARD DECO FROM A PROGRAM REAL LIFE DECO > > DEPTH TIME GAS DEPTH TIME GAS > 160-120 1 MINUTE EACH ON BG > 110 1 16/50 110 1 > 100 3 100 1 > 90 4 90 1 > 80 5 80 1 > 70 3 50/50 70 5 50/50 > 60 4 60 2 > 50 5 50 3 > 40 9 40 5 > 30 11 30 8 > 20 17 OXYGEN 20 13 OXYGEN > 10 26 20-0 8 > > TOTAL 88 TOTAL 60 > > REASONS FOR CHANGES > > 1) we start our deco at 80% of the profile in atmospheres, or in this > case , around 160 feet. We are not changing gases yet, so no reason to > sit on these stops. The ascent rate is 30 fpm, or the equivalent of a 20 > second stop every ten feet from the bottom, so we are really only adding > 40 seconds per "stop" from 80% of the profile. This actually "maxes out" > at about 5 minutes per "deep stop" in anything approaching saturations, > which I call 150 minutes for the purposes of decomprssion reality as > opposed to trying to decompress a whale. In a long dive, we also use the > first deco gas at 80% of the profile . Not in play here. > > 2) moving up we do not extend these stops per Bulhmann, since we have > already moved the "ceiling" quite a long ways above us, and are not yet > really pressing the gradient ( in percentage or relative terms, ie the > ratio of the atmospheric change deep a opposed to shallow). We need to > get to a deco gas first and spend some time, so...... > > 3) we "SIT" on the 70 foot stop for quite a bit longer than is suggested > by theory. The reason is we want to use that wide open oxygen window for > all it is worth down there to both clear the slate as much as possible, > and to move that ceiling again quite a bit so that we can abbreviate the > stops above as their ppo2 declines, rather than lengthening them as > either Bulhmann or bubble mechanics would indicate - real life says we > are correct. In fact, I have SKIPPED up to 100 minutes of our 40 foot > stops with no repercussions, and Lucy Ho can vouch for me on this ( and > the doppler says so). The other reason is that we want to give the blood > a chance to totally circulate with the new gas. While it hits the key > body parts immediately ( spine, heart, brain), it takes a couple of > minutes to get to everything properly. We do not want to hammer high > popo2's, we want to use them to our advanntage. > > 3) since we have done our deep stops and our high ppo2's, both moving > our ceiling and shortening our upper time, we can go ahead and press the > gradient as it condenses, and shorten the next few stops and get to that > oxygen. > > 4) the oxygen does not have to be hit too ahrd. I like 12-13 minute > stints with 6-8 minutes off. The reasons are that it takes almost no > time to saturate with oxygen at any ppo2 once the immediate offgassing > slows - a few minutes - and the damage starts to accrue after about > 16-20 minutes in our experience, depending of course on the dosages > already taken on the way up to this point. The swelling of the lung > tissue picks up after a few minutes, and the gas transfer process is > severely hampered. Vasoconstriction gets worse, and you are pissing in > the wind honking on the oxygen. You need to break to back gas, or in > this case , just move up and get out. > > 5) slow final ascent - the last move up to the surface is one of the > most critical. No matter how long you sit on a stop with the window wide > open, there will still be gas that will not be displaced by this method. > When you increase the gradient by trying to surface, the last of the gas > comes out rapidly and does so in bubble form. You must do a slow ascent > to reduce the risk of this, and for long dive it is one foot per minute > to the surface, for this dive it is more like 2.5 - 3 fpm. > > 6) at the surface, sit still for a bit and try not to exert for about 30 > minutes thereafter. Bubbles forming at this time will now grow as they > pick up offgassing nitrogen ( the helium is long gone) and will become > problematic later, and severely so if you have a shunt that can then be > opened by the in increasing pressure on the cappillary beds of the > lungs. > > OK - let's take it from here and get the discusion going. Please do not > copy back the whole message or it will become a mail bonb - just cut and > paste the parts you want to discuss, and lets discuss one item per > email, SVP. When we expand this to a long dive, then I will cross copy > it to WKPP@eg*.co*, and we will bring in the big guns ( Rose, Mee > ,et al). > > Let's go . > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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