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Why do a 10' stop when the PO2 of 100% is lower then 1.6? I make my last stop 20fsw. Sean -----Original Message----- From: Steve Hogan <Steve.Hogan@tr*.co*> To: shimell@se*.co* <shimell@se*.co*> Cc: techdiver@aquanaut.com <techdiver@aquanaut.com> Date: Wednesday, June 09, 1999 4:40 PM Subject: RE: Re Last Stop Depth >David, > > >>Occasionally, I do a multi-level, bimble-around-the-place dive and dive an >>air computer but deco on O2. I'm comfortable to leave the computer on the >>line or bend it when I've done sufficient deco. Note: this is based on >rules >>of thumb which allow me to do sufficient deco. > >I have done many dives using mix (usually 18/40) with 50/50 deco gas >and an air computer. Like you I am just wandering around and I use the >air computer as a guide for the deco. I have found that the air only >schedule >is longer than a mix schedule with deep stops and deco gas. There are a few >rules >though. 1. Do the deep stops. 2. Use the deco gas (50/50) for all depths >shallower >than 70 ft. 3. perform the dive like a multilevel dive (no sawtooth stuff) >This is only for some dives where a set of tables is not really >necessary (like wnadering around on a reef where the bottom is known but is >highly variable) > >Do not misunderstand me, when on a real mix dive (when I expect that the >stops will be greater than 10-20 ft) then the dive is planned and executed >on >tables (and I bend my poor computer....backup depth gauge/timer. On a dive >I did Sunday the computer informed me that I needed to stay at 20 ft while >on my 10 ft (table) stop and will finally clear 60 hrs after getting out of >the water.... I am glad it is not adaptive...<grin> It still indicated 37 >min >of deco left when I got out of the water) > >Steve > > > >David Shimell >Project Manager, Sequent Computer Systems Ltd., Sandton, South Africa. >Email: shimell@se*.co* <mailto:shimell@se*.co*> > >-----Original Message----- >From: David Reinhard [SMTP:reinhard@oc*.co*.au*] >Sent: Wednesday, June 09, 1999 5:51 AM >To: techdiver@aquanaut.com >Subject: Re Last Stop Depth > >Thanks to all who have contributed to my knowledge with your replies. >Unfortunately there are too many replies for me to respond personally to >all of you > A number of you have pointed out that air is a poor choice for >decompression. I fully agree, and it is not my practice to do so. It was >remiss of me not to point that out in my original post. Below is my reply >to David Shimell which I had intended to go to the list but I think may >have only gone to his personal email address. > >At 01:19 07-06-99 -0700, you wrote: >>David >> >>The reason there is a significant difference between a last stop at 6 vs. 3 >>is that you are doing the deco on air which is a poor choice. > >In reality I don't do my deco on air. I was just running hypothetical >profiles to see the effect of different stop depths. While I naturally >expected a difference it was the magnitude of the difference that surprised >me. While the pressure difference between 3m and 6m is not insignificant I >was particularly surprised that 1m could make such a big difference. > You are quite right, of course. Deco should be done on an >appropriate >nitrox mix and/or pure o2. But being very cautious I still deco to the air >schedule and take the safety benefit rather than do accelerated deco. So by >choosing 6m rather than 3m I have been spending a lot of extra time in the >water. However due to the large ocean swells we often encounter where we >are diving it may at times still be appropriate to go for the 6m stop. > >Thanks for your comments, Dave. > > I also received the following comment which I am particularly interested >in:- > >(quote) >"If you have done sufficient deco, then spending further time in the water >is >increasing your risk. OK, this risk is small but never-the-less a risk and >it bites some people. Doing excessive deco is therefore not adding safety." > >Do others concur with this idea? As I said above I deco on nitrox but >operate on an air schedule. In effect this would constitute "excessive >deco" for the gas I am using. So is there a problem with this practice? >Does doing extra deco increase or decrease your risk? If you are going to >increase your deco at what point should you do it, eg only on the last >stop? Come to think of it Pyle stops are in effect increased deco beyond >that required by the tables. One of the thoughts I have had about this is >what actually constitutes "excess" deco. Given the variability in deco >tables what constitutes the "right amount" of deco on one table could >constitute "too much" deco on another table. Given that we don't really >know what the "right amount" of deco actually is for any particular >individual on a particular dive profile how can we hope to know what is >"too much" deco. (The only definition of "right amount" of deco I can think >of is that amount which leaves you unbent after a dive - but you don't >really know that until after the dive, since tables are merely a hopeful >guideline which fortunately are right most of the time). > > In reality I would be very surprised if a small variation in stop >depth >made a large practical difference to the decompressing diver. If this were >the case I am sure we would have a lot more bent divers (hmmm... on the >other hand we do have a number of divers that get bent while apparently >following the tables... I wonder...). As has been pointed out the use of >nitrox/o2 for deco significantly reduces the differences I observed, so it >is even less of a problem to deco diving than it would initially seem. > > It has also been mentioned that Zplan adjusts all stop depths if you >change the last stop depth. I had noticed this and have found it >inconvenient compared to other software that keeps the same standard stop >depths and only adjusts the last stop. I guess I didn't consider the >possible effect of this change on the total deco time. I noticed another >post on this list about a new shareware deco program that does not do this, >so I would be interested in having a look at that program when it is >available. > > >Thanks to all, regards, Dave. >-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- >Ocean Internet - "The Quality ISP" >http://www.ocean.com.au/info.html > >-- >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'. >-- >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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