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Karen,
You raise an interesting point here in questioning the use of helium
mixes for dives with exposure depths of less than 130 fsw. As a first
shot you would think that the primary consderation determining the
"dividing line" beyond which you would transition from high ppn2 mixes
to low ppn2 should be the degree of narcosis or "buzz". When you can
feel a "buzz" you have probably crossed into the danger zone where not
only is there a mental impairment but a proprioceptive impairment as
well. At the other extreme is the "Wah Wah" which probably foreshadows
imminent death. The problem is that within this onset of narcosis
"transition" zone the effects of elevated nitrogen ppn2 are very
subtle. You really need to go out there and "try" a mix dive on
something you have regularly dived on air to weigh the perceptive
differences. Cobber's trimix experimentation at lower partial pressures
was really in response to George Irvine's, Robert Carmichael's and my
own recommendation that he try this and judge the benefits for himself.
From a strictly physiological viewpoint you will definitely feel less
tired and more "energetic" post dive following a lengthy exposure in the
100' range after breathing a gas mix where helium replaces part of the
nitrogen. We know that red blood cells become rigid at high ppn2s and
loose some of their hemodynamic characterisitics which benefit plug
capillary flow. On the other hand helium is a "fast" highly mobile gas
which enters the tissues rapidly and clears rapidly, thus diminishing
tissue loading in the faster compartments.
You will be amazed at the increase in your perceptive clarity while on
trimix at shallow depths. You will notice things that you previously
have overlooked and will "see" objects and events in a different
perspevtive. Cobber is correct on this one. Thanks to the abuse of
"deep air" and it's mistaken incorporation into the training agenda of
socalled "technical" diving the practice of eads beyond 100 fsw will
eventially become uninsurable.
Regards,
Bill Mee
Karen Flynn wrote:
>
> I have to admit that I've been watching the "Cobber's trimix" thread for the
past couple
> of days before posting. It just got the better of me tonight and I had to say
> something.
>
> First, Cobb admits to diving the "Eureka" off the NC/VA state border with
**mix** to
> determine the difference between a "deep air" buzz and trimix. Swears he saw
some
> difference. Come on now JIM...the Eureka's 116 fsw (35m) deep with an
occasional wash
> out to a max 118 fsw (35.9m). NOBODY'S definition of deep air, or **deep
anything** is
> in that range. Using Tx on a 116 fsw (35m) dive with a low **home brewed**
FN2 put you
> at an EAD of what....35 fsw (10.6m)??? How many of us out there notice the
"buzz"
> difference between 35 fsw and 116 fsw?? Really now!!
>
> The average REAL mid-Atlantic Tx wreck dives (Monitor, E.M. Clark, St.
Augustine,etc)
> are lying in the 240 to 260 fsw (+/-75m) range and you should be on your 6th+
**deco
> stop** before you hit 35 fsw. Matter of fact, you're first deco stop on
those dives
> would be below your max depth on the "Eureka". So maybe you got the
"pre-requisite"
> number of gas switches in to make it a technical dive - but on the
Eureka...who's
> fooling who?? Who cares??
>
> I guess I'm an idealistic gal and believe it takes more than equipment buying
savvy, an
> understanding of tech diving lingo, and a keyboard to make you a techncal
diver. Seems
> to me you should be doing the dives. Experience does matter.
>
> Karen Flynn
>
> PS: IANTD TX certified #560 ('95) and "grandfathered" out of the deep air
pre-requisite
> by Billy Deans due to level of ACTUAL Tx experience prior to the IANTD
course. Now go
> ahead - flame away...
>
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