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>Posted on 17 Jun 1995 at 18:12:10 by Scott Cherf
>At 11:52 AM 6/16/95, Chris Elmore wrote:
>> I don't know a specific formula (formulae for those across
>>the pond) but my handy Physiology of Flight manual indicates a
>>standard sea level pressure of 29.92 inches of mercury (14.69psi)
>>and 2000' is 27.82 in Hg. (13.66psi).
>>Hope this helps.
p(elevation) = p(0) exp( - alpha x elevation).
The constant alpha will depend of course on the units used.
I used to remeber the elevation at which point the airpressure
is down p(0)/e but it escapes me now. alpha will be 1 divided
by that elevation. alpha can be found using Chris's numbers:
2000':
13.66 = 14.69 exp( - alpha x 2000')
0.0726=2000' x alpha
alpha = 0.000 0363/feet.
That gives me 1/e athmospheres at 27.500 feet or 8250 meters.
Hmm, Chris better check that p(27.500') = 5.40 psi.
>Thanks Chris. To use this, I took the percentage difference between
>2000' asl and mean sea level (.07 or 7%) and adjusted the volume
>of my tank by that amount (sherwood 120 @ 3500psi, 120 cf + 7%
>= 128.4 cf @ 2000'). Then I divided 128.4 by 35 to get the cf/100psi.
>(3.66 cf/100psi). Then I timed myself breathing 100psi of gas (EAN32
>left over from my last dive) at 1900' (14 minutes). I came up with
>.262 (.27) cf/minute @ sea level.
>
>I ran the same test again, this time using my wife, and she measured
>.13 cf/minute @ sea level (took her 29 minutes to use 100 psi of gas).
>
>According to Gilliam ('Deep Diving' pp 140, 1995), the expected range
>of RMV is between .3 and 3.0 cf/minute @ sea level. This puts me at
>the bottom of his range, and puts my wife at less than half of the
>bottom of the range. For the record, I'm 6'2" 220lbs, my wife is 5'5"
>125lbs.
>
>The thing that worries me is that I only know one diver that uses more
>gas than I do on a normal dive; ie, I'm a known gas hog. Should I
Maybe you are worked up a tad when you do this test due to the fact that
you know you are a hog and wish not to be ?
Also, maybe you are too strong:
the more muscles you have the more O2 you need.
john
cc015012@br*.br*.ed*
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