Re: [PSUBS-MAILIST] PSUB Fatalities...

["Sean T. Stevenson" <ststev@uniserve.com>]

On Wed, 8 Mar 2000 18:42:40 +1300, Karl  & Shirin Fuller wrote:

>Sean,
>You are quick to rubbish someone else's figures, where are your own to
>enlighten us all ?

The point that I was trying to make with that post is that with the
rocket ascent rates created by using a lift bag or parachute/hood
escape device, the behaviour predicted by most decompression models no
longer applies, and thus ANY attempt to put numbers (or estimate NDL's)
to the profile in this case is inaccurate enough to make it not worth
the effort.  Having said that, bubble mechanics models such as Bruce
Weinke's RGBM show promise to more accurately reflect what is occurring
in the body during deco, but is still just a "best guess" as to the
physical process.  In the event of submarine escape, you have one or
more occupants who are distressed, may not have exposure protection
appropriate to the water temperature, may have been breathing elevated
PPO2 during the escape, and then shoot to the surface like a ballistic
missile.  That's enough to make any decompression modeller quit the job
and take up golf.

>Do I understand that you are saying, that at a depth of 90 meters, you have
>a pressure of 2.1 atmospheres ? At 1 atmosphere per 10 meters, I think you
>have made an error Sean.

Oops.  I meant to say that at a depth of 90 meters, the partial
pressure of oxygen in what was previously air at 1 ata will now be 2.1
ata.  The total ambient pressure is of course 10 ata.  While PPO2's of
1.6 to more than 2 can be routinely tolerated in a dry chamber, once
the person is immersed, the pressure is no longer acting equally at all
points but rather in a gradient across the lungs.  For example, a
person in a vertical position experiences a difference in pressure from
the top to the bottom of the lung of about 10 inches of water column
head.  While this does not immediately seem to be a significant
difference, experimental results have indicated that it adversely
affects the body's tolerance to elevated levels of oxygen, and prompted
the NOAA (and subsequently most diving training organizations) to
establish a maximum limit of 1.6 ata oxygen in the water.

Karl.