Extreme Medicine: How Exploration Transformed Medicine in the Twentieth Century by Fong M.D. Kevin

Author:Fong M.D., Kevin
Language: eng
Format: mobi, pdf, epub
Publisher: Penguin Group US
Published: 2014-02-06T00:00:00+00:00

November 2011: Me diving in the Red Sea using a vintage scuba rig of the type first seen in the 1950s.

(© Michael Pitts)

WATER

Brace! Brace! Brace!” he shouts, running the words together as though they were one. I shove my head up against the wall of the helicopter, my crash helmet clunking against the bulkhead, and fold my arms over my chest, hooking my thumbs under the shoulder straps of the four-point harness. We hit the water in darkness and immediately begin to sink. The water is already at my ankles. I rest my right hand on my harness’s quick release, and with my left I find the handle that will jettison the door. Once underwater, the helicopter will sink a meter every second.

I never used to understand how it could be difficult to escape from a sinking vehicle. Open the door, swim out and up to the surface. How much of a challenge could that be? On dry land, I can hold my breath for the best part of three minutes, and I’m an OK swimmer. How long could it conceivably take for me to get to the surface from, say, twenty meters down? But of course you have to factor in the harsh realities of the physics and physiology of your predicament. How long could it take? Very probably forever.

This is HUET (pronounced hew-it), the Royal Navy’s Helicopter Underwater Escape Training facility in Yeovilton. It exists to provide helicopter crews with the training they need to escape a vehicle that has ditched in open water. The work they do is vital. In more than 80 percent of helicopter crashes over water, the time between warning and impact is less than fifteen seconds. Of these, more than 70 percent sink immediately, with over half of them inverting. The military’s experience of helicopter accidents into water is also pretty sobering. Of those occurring in daylight, the survival rate is 88 percent. But for survivable helicopter crashes into water occurring at night, that number is as low as 53 percent.

But why is this happening? These are healthy people, trained military personnel, and in most cases strong swimmers. The answer lies in the very structure of our bodies.

—

WE TAKE OUR NATURAL BUOYANCY for granted—mainly because the vast majority of us never dive beyond the point at which we are more likely to sink than float. From the surface, for the first seven meters or so, it takes a bit of effort to dive below the waves. The air in your body, principally that in your lungs, serves as a kind of float to keep you buoyant. Here the upthrust you experience by virtue of the good old Archimedes principle is more than enough to return you to the surface.

But below those few meters, the relationship is reversed. Your tissues become compressed, the volume of air in your lungs decreases as the pressure mounts, and you eventually become denser than the water around you: an object that would rather descend into the depths than float upward.

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