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Old 05-12-2016, 19:19   #16
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Re: Survives Underwater for 60 hours

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Originally Posted by Teknishn View Post
Shrew, some rather simplified basic dive theory here for you. For every 10-meters of depth, atmospheric pressure on the human body doubles, we compress. Oxygen and Nitrogen molecules are also compressed to 50% of their original size on the surface. Since normal human breathing patterns don't change with depth, one is now breathing in twice as many oxygen and nitrogen molecules at 10 meters of depth than they would normally breath in on the surface. For each additional 10-meters the Oxygen and Nitrogen molecules are further compressed by 50%.
The doubling of pressure is only true for the first 10 meters. 10 meters down gets you to 2 atmospheres of pressure. To double again to 4 atmospheres you would have to go to 30 meters not 20 meters.

The oxygen and nitrogen molecules don't compress or change size, the space between them is reduced as the pressure increases.

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Now, we inhale and exhale oxygen and nitrogen. Our bodies use oxygen to support life functions, we burn it off and exhale some of it. Nitrogen however, being an inert gas, is not used....but is still absorbed into our bloodstream and we only exhale part of it. Oxygen off-gases very quickly since we use some of it. Nitrogen on the other hand, does not leave our bodies as quickly as it is also a denser gas.....it takes time for our bodies to get rid of it. This is where decompression stages in diving are important. It allows our body to off gas/dissipate the nitrogen that is still in our bloodstream.
Oxygen is metabolized by the cells and not outgassed from the blood stream except for a amount that is so small it can be safely ignored. That is why high partial pressures of oxygen are used in mixed gas diving and rebreathers.

Nitrogen is dissolved in the tissues and blood. Some tissues absorb quickly and other slowly. 16 diffusion compartments are used in the Bulman decompression algorithm. The nitrogen comes out of the fast tissue quickly and the slow tissues slowly as the pressure is reduced. The out gassing rates have little to do with the density of the gas as it leaves the tissues and is scavenged by the blood. The decompression schedules have more to do with the varying diffusion rates of the tissues than the density of the gas.


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If one were to ascend from 100-feet (in the case of this sailor) without adequate time to get rid of the accumulated nitrogen molecules in his system, as he would rise up towards the surface, the nitrogen gas molecules compressed by depth, but still in his system, would start expanding to their original size as depth decreases. This would lead to what are called "The Bends" which can cause severe arterial damage as the gas bubbles expand beyond the limits that one's joints, arteries and veins can withstand and can cause permanent injury and in some cases, death.

Like I said, a simplified version. If you want to really understand how it works, taking dive course is a good place to start. Lots of books out there on dive theory and dive medicine as well. Some good reads if you're a diver (which I am).
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Old 06-12-2016, 06:19   #17
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Re: Survives Underwater for 60 hours

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If you want to really understand how it works, taking dive course is a good place to start.
Many thanks. I can't dive, so I won't be taking a dive class. I have an inner ear issue in my right ear that prevents proper pressurization/de-pressurization. My ear has been partially blocked just about my entire life.

I appreciate the replies. My misunderstanding was assuming there was sea level atmospheric pressure as a result of being inside of a rigid structure. It didn't occur to me that the water from below would compress the air in the bubble. That makes sense. Many thanks.
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Old 07-12-2016, 07:46   #18
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Re: Survives Underwater for 60 hours

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How much air does a frightened, freezing person 'consume' over 60 hours?

It had to be a big air bubble, no?

b.
Actually, the water temperature and the fact that water conducts heat far more readily than air may have saved his life by reducing physical activity by panacking. But that is a long time to be in a blacked out space. Since sound travels so well underwater, he may well have heard the divers and the boat so been waiting and then the glow of a divers torch given the signal to risk everything with a free hold dive.

There was an interesting study into casualties during the various battles for the Falklands. Casualties were layed out on the ground and a poncho/stretcher if they wre lucky. The cold temperatures 50' south in April/May; heading into winter meant that loss of body fluids was reduced by the cold helping to maintain some circulation to vital organs and reduce shock.

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Old 07-12-2016, 11:44   #19
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Re: Survives Underwater for 60 hours

I am not sure.

I think given the information in the article, the amount of air in the air pocket was not sufficient to survive 60 hours.

I think the article may contain an error.

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Old 07-12-2016, 12:30   #20
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Re: Survives Underwater for 60 hours

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I am not sure.

I think given the information in the article, the amount of air in the air pocket was not sufficient to survive 60 hours.

I think the article may contain an error.

b.
If the pocket is 4 ft sq (article) then guess 7 ft high. That is 112 cubic ft of air. I saw the video at the time he was rescued and it was not a 4 x 4 ft space. Makes for dramatic fake news.

As an aside, any local news article on a topic or incident that I have first hand knowledge of is usually very flawed. I then extrapolate this lack of precision to all of the news and especially political news
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Old 07-12-2016, 13:45   #21
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Re: Survives Underwater for 60 hours

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Originally Posted by LakeSuperior View Post
If the pocket is 4 ft sq (article) then guess 7 ft high. That is 112 cubic ft of air. I saw the video at the time he was rescued and it was not a 4 x 4 ft space. Makes for dramatic fake news.

As an aside, any local news article on a topic or incident that I have first hand knowledge of is usually very flawed. I then extrapolate this lack of precision to all of the news and especially political news
I would think the air pocket would have been much larger to start with, assuming some may have been leaking out over time. I dought a hull/cabin would be 100% air tight. Besides he had 3 times the amount of oxygen then what the space shows. What you don't use gets exhaled and used later. And with his body being cold he would use even less then normal.

I can't imagine what thoughts were going through his mind in those 60 hours. As a diver I would have found my way out and ascended to the surface once the boat settled. At 100 ft one can be down about 15 - 20 minutes before needing to decompress. I've done a lot of free diving and it's a lot easier to ascend then to descend! The guys ears must have been hurting, or even perforated once on the bottom.
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Old 07-12-2016, 13:55   #22
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Re: Survives Underwater for 60 hours

The amount of oxygen was the last thing to worry about. Two main problems are CO2 buildup and hypothermia..
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Old 07-12-2016, 14:09   #23
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Re: Survives Underwater for 60 hours

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The amount of oxygen was the last thing to worry about. Two main problems are CO2 buildup and hypothermia..
C02 is heavier then air. Keeping ones body as high as possible would alleviate most of it. There was no mention of him having a headache, which would be the symptom of CO2 poisoning?

Just saying......
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Old 08-12-2016, 00:29   #24
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Re: Survives Underwater for 60 hours

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C02 is heavier then air. Keeping ones body as high as possible would alleviate most of it. There was no mention of him having a headache, which would be the symptom of CO2 poisoning?

Just saying......
It gets mixed very easily though, so unless he was high and still, so it would be an issue. Not dramatic until you hit 10% CO2 ish. Cave divers have started using fan forced CO2 scrubbers in UW habitats to solve this.

As an absolute minimum an adult uses .5 litres of O2 per minute. Any movement and that pushes up to 0.7 or 1.0. So O2 consumption would have been an absolute minimum of 1 cuft / hour. So for 60 hours, 60 cuft O2, requiring 300 cuft of free air at one atm pressure. At 30m / 4 atm pressure that equates to a space approx 80 cuft in size full of air, so the numbers kind of work.
Being under pressure helps, as the PPO2 would have been 0.8 at the beginning, and you're probably OK down to a PPO2 of around 0.14 ish - ie you can consume a much higher % of the available O2 than you can at the surface. C02 would be the limiting factor I would think - and lead to a really horrible end as your breathing rate goes nuts due to not being able to get rid of CO2.

While from the arm chair it's easy to say that you'd free dive out, remember that it's dark, and you have no idea at all how deep you are. I've been silted out in caves and wrecks a few times (with a guideline) and it's incredibly disorientating. Particularly wrecks 'vewhich are upside down, or on their side. If there was some light to see by and I knew the way out, I'd probably have a crack... but it would be hard. Any more than 20 metres distance required through the wreck, and I don't know if I could make it. And I have free dived to those depths before (that's about my limit though)

Very lucky!
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Old 08-12-2016, 10:28   #25
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Re: Survives Underwater for 60 hours

Yeah, it's all speculation. The dread or dismay the guy must have been going through is a fear a lot of sailors probably have, with little control of ones destiny once a ship/boat goes down. He profited by hanging on until the last breath!
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