Raising the Dead: Nightline Fri

[ethanb]

Dr. Clarke of the Navy's Experimental Diving Unit gave an excellent talk at the 2005 NSS-CDS Workshop about the accident.  I looked for a copy of his presentation online and can't find it, so this is from memory.  The main point of his talk was that Shaw died from excessive CO[sub]2[/sub], most likely due to the high work of breathing (WOB) diving (and working) at such a depth.  The Mk15.5 rebreather he was using was intended to have a maximum depth of 200-300 ft (I don't remember exactly) and the designers never conceived that it would be used at nearly 900 ft.  At these depths, breathing gas has a density nearly 30 times what it would be on the surface.  Compounding the problem was the fact that Shaw used fine-grain (8-12 mesh) CO[sub]2[/sub] absorbent material in his scrubber canister, instead of the standard (4-8 mesh) material.  While using the finer grain material increases the surface area, improving scrubber life and efficiency and reducing inspired CO[sub]2[/sub] levels, it also further increases the WOB.  Higher WOB leads to shallower breathing, which means that the lungs can't efficiently exchange CO[sub]2[/sub].  Very high WOB can lead to extremely high levels of dissolved CO[sub]2[/sub] in the blood (even if the inspired gas has no CO[sub]2[/sub]) and this can lead to death.

Dr. Clarke's talk included some quotes from Shaw about why he chose to use the finer grained scrubber material.  The one quote I remember was along the lines of "For deep dives, I always use the highest quality fine-grained scrubber material to get the longest canister life."  While that true, perhaps Shaw did not fully consider the negative impact this would have on WOB.

Dr. Clarke also analyzed the grain size distribution of various scrubber materials and concluded that the material size distribution can vary widely.  This is bad, as it leads to tighter packing of the scrubber, increasing WOB. 

In any case, it's a very sad story (my thinking is it was a huge waste just to recover a body), but death can be the price one pays for being the first, for exploring and pushing the limits of human existence.  I'm just glad there are other people out there who want to do it. 

Ethan