Hi Hans
I will not go and say I know what you are saying happens to the body. My 
experience tells me that we as TECHNICAL divers carry  stages with a higher 
deco mix than is being talked about. But I do not count this as a bailout 
option as it is meant as deco gas only  and  rigged as a stage cannot be 
put in my mouth by mistake at the start of a dive. The same cannot be said 
for rec. diver that is where this debate started I think. Most rec.divers 
back mount the pony and should never have anything in it but bottom gas. To 
put the 39% in your mouth by mistake at the start of the dive to 130ft will 
put the diver at 1.9 far longer than the few seconds being talked about. 
This is a real risk, I have seen it happen on one occasion. I also believe 
that is what killed Harvey in 1998 if I remember right. If this has already 
been said I missed it. Someone correct me if I am wrong here. I am lost as 
to how this got started.




  At 01:01 AM 2/5/00 +0100, Hans Petter Roverud wrote:
>At 11:53 AM 2/4/00 -0500, Robert Wood wrote:
>
>
>>Steve Schultz wrote:
>> >
>> > I think I know where this absolute bullshit is coming from.
>> > During my TDI Basic Nitrox course, they actually recommended carrying
>> > EAN39 as a bailout gas for MOD 130.  "you'll only be breathing the mix for
>> > a few seconds until you can get to the proper depth".
>
>Actually, this may be correct -- the risk of a hit is low if you get up 
>from 1.9 ASAP. However, the benefit of breathing a high PO2 for a few 
>minutes is negligible as well. The good doctor seems to believe he gains a 
>worthwhile deco benefit from spiking his bail-out. If so, we'd be in a 
>real risk versus benefit situation. However (that's a fancy "but" again), 
>a pony is way too small to provide enough gas for enough time to make the 
>gradient work. A pony is good for getting out without inhaling water -- 
>it's not good for deco.
>
>Now, if you carry a stage rather than a pony you'll get enough gas for a 
>proper deco but then you won't have to spike the PO2 to get out on a rec 
>or light tech dive in the first place. The idea of spiking the PO2 to make 
>a pony suffice for deco doesn't work since you need time (blood turnover) 
>as well as absence of inert gas to accelerate your deco. There's really no 
>way to accelerate a deco within the capacity of a pony cylinder, in other 
>words, a moot or a mute point :-)
>
>BTW, George is absolutely correct on the immersion effect -- don't you 
>ever believe you can take a high PO2 underwater since you can take it in a 
>dry chamber. The brain auto-regulates oxygen up to a PO2 of about 2.0 all 
>right -- in the absence of CO2 stress and the presence of a normal 
>gravitational pull on the blood circulation. Once submerged, the brain's 
>auto-regulation is severely limited. Blood normally pooling in the legs is 
>being "freed" and the ensuing hypervolemia will counter cerebral 
>vasoconstriction. In plain English, the brain tries to choke down the 
>blood supply while the high blood volume forces the arteries open.
>Result: far more oxygen than the brain wants!
>
>Conclusion: I wouldn't worry too much about 1.9 for 5 seconds but it won't 
>do anything for my deco anyway so why risk it?
>
>regards,
>
>Hans
>
>
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