Posted by MHK on July 30, 2001 at 10:06:39:
In Reply to: Re: moderation>Repex and CNS posted by Kendall Raine on July 30, 2001 at 08:35:05:
Kendall,
Clearly the 8 hour stuff is done in the habitat, but I'm not sure that accounts for the total differences. Because when we so Cheryl, for example, which does not have a habitat and we still run 3+ hours on 02 it is done absent the habitat.
My understanding from George and JJ is that they way they were able to extend the NOAA limits is that they realized that by getting off of the 02, in other words not running continuos 1.6's, they were actually more efficiently off gasing. As you know, 02 is a vascular restrictor, so by taking a *back gas* break they found that allowed for more efficient blood flow when they actually got back on 02.. George was telling us when he was here last week that they initially started taking breaks at 1/2 hours, then they reduced it to 20 minutes and they are now experimenting with 12 minutes..
Now I've tried to be clear that you can't compare what they do in Wakulla to a recreational diver, but my point was that by blindly following guidelines that were set in teh 80's and not knowing what went into the guidelines is frustrating to me.. The 1.6 and then the resulting 1/2 hour increases in time when you drop your P02's, you'll see this wasn't a true scientific conclusion inasmuch as it was based upon the fact that during the initial study that had the first diver seize at 45 mninutes using a 1.6, but then you didn't have another one for about a 1/2 hour and by the time you got to 1.1 the seizure rate was largely irrelevant. Accordingly, if you read the studies you'll see the conservatism rate is so extraordinarily high so as to be a source of concern for me..
In other words, I'm NOT suggesting that diver's abandon the 1.6 if they haven't done the research, haven't done the homework or don't understand what is involved. The entire discussion was premised upon Steve offering up the fact that he was comfortable calculating CNS percentages underwater, but wasn't comfortable calculating NDL's, so I was trying to find out why the inconsistency since in my view, calculating NDL's are a snap and if for some reason you make a mistake the penalty may be a DCI hit, whereas CNS clocks are more complex and if you make a mistake the result is usually fatal so I was trying to understand the logic..
I've previously advised how we calculate underwater the NDL's and I've provided reasons why..
When computing the OTU's the formula is
t(PO2 - 0.5) / 0.5) to the .83 power.. I'm not sure that calculating these type of exponents in-water is practical.. Whereas I'm confident in saying that once the theory is learned and understood the predicition of tolerable OTU's is more practical..
As you know, we can't teach a class on the internet so I'm trying to get people to open their minds and understand what goes on behind the numbers.. The vital capacity decrements, the UPTD's the OTU's the KP factor's etc. etc..
It get's frustrating sometimes when we had the discussion about computers and NDL's a few weeks back we had the opposing side accuse me of giving potentialy fatal advise and suggesting that our methods actually limit bottom time as opposed to a computer. Now when we are talking about oxygen toxcicty the suggestion is that it's possible to perform in-water OTU calculations, but that NOAA says 45 minutes. So all I'm doing is opening up the discussion and providing what goes on behind the numbers and why I believe 1.6 is NOT an absolute, and if someone argues otherwise I just want to be told why, other than * because NOAA says so*... Clearly, given tha fact that the WKPP does it week in and week out, suggests that there may be some problems with such a stringent absolute..
NOAA suggests 45 minutes, and routinely it's done 8 hours without incident, if that doesn't spark interest then there isn't much more I can do about it...
Later