Tragedy at Mavericks & Shallow Water Blackout

There needs to be an unfortunate update to my post on The Twelve Second Rule

Sion Milosky’s tragic drowning death at 40-50 foot Mavericks illustrates the dangers of combining huge powerful waves with human limitations. Even a buoyancy vest didn’t help Sion. My sympathies and prayers for his family and friends–a tragedy in every sense of the word.

By some accounts Sion was held under for two set waves. Completely from an armchair perspective, and speaking with respect, for a big wave rider, it seems to me that two set waves should theoretically be survivable. Let’s say there was a twenty-five second period, so he would have been under for 25 seconds on the first one, and then hit with the second wave and held under for another 25 seconds. A minute, a minute and a half, isn’t the limit for these guys, so I’m wondering if he was held under for a third wave. It’s also possible the immense volume of churning water created underwater boils currents that kept him sucking him down.

Or maybe the lesson is brutally simple: a fifty foot wave can kill even the best prepared.

There’s another danger for free divers and surfers called shallow water blackout. This is often associated with hyperventilation, but not always. Briefly, what happens during shallow water blackout is that even at 10-15 feet under water the lungs are compressed. After some time underwater, under compression, the lungs still hold enough oxygen to maintain critical supply to the brain. But as the diver or surfer makes it to the surface, the expansion of the lung abruptly dilutes the concentration of the vital oxygen to below the threshold necessary to maintain consciousness. The person blacks out in shallow water and will drown if not rescued.

Contrary to popular belief, hyperventilation does not increase oxygen content by saturating the blood with O2. What hyperventilation does do is purge carbon dioxide from the blood. It reduces the CO2 content. Now, if you hold your breath, it is the CO2 buildup that triggers the need-to-breath impulse, which can be pretty damn imperative (although in fact you can hold your breath longer than that, because you still have enough oxygen). If you hyperventilate and decrease the C02 levels, then you don’t feel the need for a breath when in fact you are running dangerously low on oxygen. As you rise to surface, that’s just enough for the O2 levels to drop below the threshold, and you black out.

So is there any benefit to hyperventilating in large surf? You see a macker set on the horizon, should you start pumping your lungs like a freight train? It seems to me that the only benefit would be this: as you are pummeled to the bottom and ragdolled along, if you don’t feel that burning need for air, then you won’t panic as quickly trying to fight for the surface, and so in turn you will conserve the oxygen you do have. But it doesn’t give you any more oxygen.

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