Having nitrogen in the breathing media:

1)  is cheaper than using heliox

2)  is a slower diffusing gas than helium, and thus will decrease your
decompression obligation slightly as compared to heliox for some bounce
dives, and

3) when present in small amounts, has been shown to retard the onset of
high pressure nervous syndrome (HPNS) in deep commercial exposures or
when compression to depth takes place very rapidly.

Your father, however, is probably right, since helium is easier to
decompress from, having a much lower potential for physiological
damage.  It is also effectively non-narcotic, and in reducing the
density of the breathing media, reduces overall breathing effort.  For
technical divers, cost is the primary reason we are not all using
helioxes.

-Sean



On Mon, 5 Apr 1999 17:11:31 -0600, Scott &/or Julie Gudmundsen wrote:

>I don't know a thing about trimix, but it interests me as I am pushing the
limits of deep air.  My father, a non-diver,  who has a Ph.D. in physics, asked
me the following question.
>
>It's my understanding that trimix is part helium, part nitrogen, and part
oxygen. Why does it contain nitrogen? Wouldn't it be better if it contained no
nitrogen at all?
>
>I told him, "I have no idea, but I can find out!"
>
>Please edumicate me.
>
>Thanks!
>
>Scott Gudmundsen
>Vernal, Utah
>


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