From:	Tim Cooper <tpcooper@***.CSUPOMONA.EDU>
Subject:	Re: Underwater breathing
Date:	Sat, 30 Nov 1996 18:04:27 -0800

On Sat, 30 Nov 1996, Glenn Robertson wrote:

> >
> > The other problem is the gas mixture. From memory (and name) the O2 gas
> > tank is pure O2.
> No, it doesn't have to be. You can put any mix you want in there. At
> the hospital we have varying mixes. Mostly pure oxygen tanks, granted,
> but we have two different heliox varieties, various mixes of regular air
> and anesthetic, and for machinery even tanks with oxygen, carbon dioxide,
> and nitrogen. So, you can put any gas mix you like in a tank.
>
>
> > This has serious ramifications if we were to reinflate
> > with just O2. Hence, a better "air" mixture is needed. If reinflating
at
> > sea level, then an air mixture can be used. If in an underwater city or
> > something, then the pressure would require another mixture, to compensate
> > for the partial pressure of O2. So a helium/oxygen mix could be used.
>
> There is nothing wrong with using pure oxygen in tanks as I recall, unless
> you are an infant whereby you can get Retrolental Fibroplasia (RLF) and go
> blind like Stevie Wonder. Afterall, many patients at the hospital get
> pure 100% oxygen. Also, some patients on ventilators get 100% oxygen,
> which is important because they don't get any outside air entrainment.
> Oxygen doesn't cause alveolar collapse.
>
> Just my respiratory two cents.
>
> Glenn
>

I'm not sure if this applies, as I've not been following the thread too
closely, but I thought that a conventional "air" mix becomes quite lethal
at very high pressure...something about the oxygen concentrations and
pressure - net result is severe damage to the lungs. Thats why they
routinely use a mix with helium for extreme depth excursions. (Please
correct if I'm wrong, I'll try to remember where I read that..)

~Tim