Posted by MHK on October 10, 2000 at 09:20:35:
In Reply to: Re: Effect of Helium posted by Eins on October 09, 2000 at 22:43:39:
Eins and Kelphead,
This is in response to both questions..
Kelphead, we generally use Nitrox from 1' - 100'. Although it's clear that you could use He as well, it is somewhat cost prohibitive to incorporate He into dives in the 1' - 100' range. Several prominent pioneers are now using He in their decos gases at the 70' - 20' stops, but that is different than using it as a breathing gas..
As for the comment respecting breathing pure He, it would cause substantial problems since a person needs atleast a 16% oxygen content to avoid hypoxia.
However. overall and very briefly, He is a much friendlier gas inasmuch as it off gases 2.65 times faster than N2 and more importantly He does not enter the slower tissue compartments. This is of significant benefit when incorporating deep stops into your ascent. If you have planned your ascent properly by the time you get to your 15' stop basically all your fast tissue compartments are free of He, they have not accumulated as much N2 and while at the 15' stop you are merley cleaning up the slow tissue compartments that also have less N2 than you would normally have..
In terms of physiological benefits Helium is vastly more beneficial, the main draw back is cost. To the extent that He were cheaper it would surley be the norm.
Jim could probably answer this question better than me, but in ball park figures what most divers compare is the following:
1 tank of air $4.00
1 tank of Nitrox $9.00
1 tank with a Triox ( using 20/30 for example purposes) approx $25.
As I said these are rough estimates so don't beat me up to bad if they are a couple of bucks off.. These are for illustartive and comparitive purposes..
So in reality most diver's say, well I dive 2 or 3 times a month and if I had to pay $25 for the mix it would certainly add up so I'll just dive with air...
However, I would urge anyone doing dives in the 100' - 200' range to take a long hard look at this medium because the benefits are substantial and the economic outlay will really come in handy if you have a problem and then you have a much clearer head to be able to solve it...
The use of Helium should very much be considered, however we can only provide a brief overview on these type of forums and we strongly recomend that prior to undertaking the use of He that you enroll in a quality course respecting it's use...
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