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At 09:30 PM 10/16/2000 -0700, Paul Braunbehrens wrote:
Hello Paul,
>DIR is against the use of ponies, so you can leave that part out.
>Exact reasons why would be welcome.
- Ponies are an entanglement hazard. They're hard to see and hard
or impossible to remove underwater in the event they get entangled.
Also, they can "key" you into a restriction where being unable to
remove it could cost you your life.
- If you need more gas, it's likely due to one of the following:
1. High-drag gear configuration. In this case, consider
streamlining your gear.
2. Out of shape diver. In this case, consider a gym
membership. :)
3. Long bottom times. In this case, you're probably doing
a planned decompression dive, and you should be diving
manifolded doubles with full redundancy, not a pony.
- If you want a pony in case you have an air failure, consider that:
1. If you have a downstream-design regulator (very likely) then
the failure mode is a free-flow. Even with an all-out free-flow,
it will take a long time to drain your tank; certainly enough
time to get to the surface. Try it in the shallow end of a
pool sometime.
2. You have (or should have) a buddy who can share air with you
in the event you do manage to run out.
>As far as deep air goes, what
>constitutes "deep",
This is a topic of much contention. My opinion is that anything
beyond 100 feet or so is definitely deep enough to add helium. There
are lots of reasons for this but I'll list a few off the top of my
head.
1. When I go hunt lobster in 70 feet of water off the southeast
Florida coast, I nearly always catch the limit when I'm on mix.
Yes, even in 70 feet I breathe mix. When I do the same dive on
air, I can't quite catch as many lobsters. I don't *notice*
narcosis on air at 70 feet, but the lobster-count evidence is pretty
hard to ignore. In an emergency, I want to have available whatever
mental faculty allows me to catch more lobster. Diving mix
gives me that.
2. I haven't dove air below 100 feet in a long time. My first-hand
experience tells me what a bad idea this is and objective experiments
(see below for references) confirms my experience. Narcosis
adaptation by non-saturation divers is a *myth*. Adaptation
does indeed appear to occur, but only after multi-day *continuous*
exposure to high PN2. Itinerant divers can overlearn some skills
to help compensate for narcosis to some extent, but an emergency
requiring a new, non-overlearned skill (which emergencies have a
tendency to be) can be a death sentence under high PN2.
3. High PN2 causes subtle, *irreversible* damage to the body. I'm
not making this up or parroting others' opinions on this. This
fact is documented (see below for references).
>and some references to actual fatalities brought
>on by deep air (and I'm not talking 400 feet here, but people who
>kicked the bucket doing what a rec. diver might do on a deep air
>dive).
I'll leave this one to someone else. Too morbid for me to go off and
put together a list for ya.
References:
Kiessling & Maag 1962, Performance Impairment As A Function
Of Nitrogen Narcosis.
Case & Haldane 1941, Human Physiology Under High Pressure.
Bennett & Glass 1961, Electroencephalographic And Other
Changes Induced By High Partial Pressures Of NItrogen.
Fowler 1973, The Effect Of Hyperbaric Air On Short-Tem And
Long-Term Memory.
Kiessling & Maag 1962, Performance Impairment As A Function
Of Nitrogen Narcosis.
Frankenhaeuser 1963, Effects On Psychomotor Functions Of
Different Nitrogen-Oxygen Gas Mixtures At Increased Ambient
Pressures.
Fowler 1973, The Effect Of Hyperbaric Air On Short-Tem And
Long-Term Memory.
Bennett, The Effects Of High Pressures Of Inert Gases On
Auditory Evoked Potentials In Cat Cortex And Reticular
Formation.
Bennet 1963, Neurophysiologic ANd Neuropharmacologic
Investigations In Inert Gas Narcosis.
Bennet & Elliott 1993, The Physiology And Medicine Of Diving
There are tons more. This is not a poorly researched field.
-Mike Rodriguez
<mikey@mi*.ne*>
http://www.mikey.net/aue
Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n
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