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Surviving underwater in an air bubble

A news story in June resonated uncomfortably with me: a Nigerian sailor survived for two days in a pocket of air trapped beneath the tugboat he was in, which capsized in heavy seas. The tug was servicing an oil platform off the Nigerian coast.

I was immediately reminded of the Miroshga, an unseaworthy whale watching vessel that capsized in appalling conditions off Hout Bay in October 2012. The boat had its bilge pump installed UPSIDE DOWN, and was rated for over 40 passengers when it’s only five metres longer than our boat – which can take seven passengers (and when Seahorse is fully loaded, she feels full). Furthermore, the Miroshga hadn’t had a SAMSA inspection since fundamental changes were made to the vessel and its engines. The money-hungry decision to head out in a 25 knot south easterly wind and high seas was incredibly irresponsible.

Most people who go on seal cruises, whale watching or cage diving don’t spend half their lives on or near the sea, and simply don’t have the tools to assess whether conditions are safe and whether the boat is seaworthy. The passengers trusted the charter operator and SAMSA, and were badly let down. One man drowned, and three women were trapped under the boat in pockets of air for several hours, their limbs dangling in the freezing water, until rescue divers brought them out. I cannot imagine how traumatic the experience was for them. The rest of the passengers were rescued by a boat full of poachers, and by some incredible NSRI volunteers. It was a shameful day for the boat charter operators, and for those responsible for legislating and enacting maritime safety provisions in South Africa.

I digress. What happened in Nigeria? Out of the twelve crew on board the tugboat, ten bodies were recovered, one was lost, and the twelfth crewmember, Harrison Okene, was discovered alive, under the boat in 30 metres of water, surviving by breathing from an air pocket. Upon being rescued by divers sent to retrieve the crew’s bodies (can you imagine their shock at being greeted by a living person when they were expecting only corpses?), Okene had to undergo sixty hours of decompression in order to avoid being bent. He’d been breathing air at four atmospheres for two and a half days!

The incident prompted a fascinating discussion on StackExchange, a discussion forum for a variety of disciplines (I lurk in the statistics and quantitative finance forums). A user posed the question:

How large does the bubble have to be so that a person in it can have indefinite supply of breathable air?

The reason it’s even possible to have an “indefinite” supply of air is that if the bubble is large enough, oxygen will diffuse out of the surrounding water back into the bubble, and carbon dioxide won’t build up to fatal concentrations. You can read through the discussion if you want to (fun to see physicists arguing, nice if you like formulas!) or there’s a news article here about the theoretical bubble size that would be required for survival. Turns out the actual air bubble was close to the size calculated by the physicists that would allow survival for at least the time that Okene was submerged. Lucky, lucky man!

Update: Here’s the helmet cam video from one of the rescue divers who brought Mr Okene to the surface. The text at the beginning is wonky – persist. Note the South African accents! The diver’s voice is squeaky – I think because he’s breathing a gas mix with helium in it. It gets good at about 5:30 but it’s extremely interesting to watch in its entirety to see what sort of conditions these divers work in, and how the surface support talks them through their tasks and keeps them calm.

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Clare

Lapsed mathematician, creator of order, formulator of hypotheses. Lover of the ocean, being outdoors, the bush, reading, photography, travelling (especially in Africa) and road trips.

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