Loss of human body volume vs depth (buoyancy)

[Wibble]

I am not a freediver.

About 5 years or so ago I said something in a thread that was consistent with what the majority in this thread are saying about the body not compressing at depth. A couple freedivers responded as if I had written the most ignorant, stupid thing in the history of ScubaBoard. How could I know so little about free diving? One person in particular essentially told me to hide my face in shame forever, but, then, that was the topic of many of his posts anyway.

Having learned my lesson, I recently wrote a post in which I mentioned the body compressing at depth, and someone responded as if I had written the most ignorant, stupid thing in the history of ScubaBoard.

I am still not a freediver, and I have no intention of becoming one, but I would sure like to find out so I can stop being perceived as the person writing the most ignorant, stupid thing in the history of ScubaBoard.

Freediving isn't natural. Yuck, what's the point of a few seconds underwater when you could spend hours

 

[Subcooled]

Human compressibility is an interesting question.

Lungs, of course, are filled with compressed (=high pressure) air/gas while SCUBA diving and will not collapse. Lung collapse in freediving is a real issue, though.

60% of the body is water and water is practically uncompressible.
I find it improbable (no real knowledge) that bones would compress.

The rest, I do not know.

Something happens though:
Compression arthralgia - Wikipedia

 

[Pressurehead]

Prof. Farina should have settled the issue of human compression at depth. If not, let's call in some folks who've been down to dozens of atmospheres.

How about it, @Akimbo and @Pressurehead? Do you start tripping over your bell bottoms as they bring you to working pressure?

Such fun.
After reading some funny stuff on here, 'Boyle's Law' [as one of many, we all learn about as "pressure heads"] we also find that as pressure increases, brain decreases , just joking, someone will think I am serious.

 

[inquis]

... in the pool minus your wetsuit. If you can suspend yourself mid water with no air in your BC [...] you should be fine with no ditchable weight.

I don't see how that follows since the wetsuit is the lion's share of what the BC should be compensating. (The other piece to compensate is the weight of the air you haven't yet breathed.) What happens when your 7 mm suit is compressed at 100 ft and you lose, say, 20 lbs of lift? That additional weight will be on you to raise if the wing totally fails. Anyone who has a 7mm suit should really measure its buoyancy as @johndiver999 described to ballpark the worst-case swimup. Even better is the bottom-line, actual swim up from depth with empty wing.

An alternate approach to estimate how much you can swim up can be done in a pool wearing a bathing suit and fins. Tread water while a buddy adds weight to a mesh bag until you have to drop it. Have the buddy also hold a line to the bag (to catch it when you drop it) or use coated weights to avoid damage to the pool bottom.

 

[MaxTorque]

It would actually not be that hard to measure the compressibility of a wetsuit!

Just need a suitable pressure vessel, fill with wetsuit and water, then plot the pressure vs water volume pumped into the vessel, and hey presto, you have the "spring rate" and volumetric rate of your wetsuit.......

 

[Akimbo]

How about it, @Akimbo and @Pressurehead? Do you start tripping over your bell bottoms as they bring you to working pressure?

I never actually checked but the NEDU probably did. Captains Bond Mazzone ran the early sat divers through hell collecting data. Maybe @Duke Dive Medicine has seen studies.

I suppose you could measure it if you looked close enough. Compression arthralgia (compression pains) symptoms are largely avoided by slowly compressing saturation divers. I never saw the actual numbers on disc compressibility but I wouldn't be surprised if a diver's overall height change could be measured after a fast blow-down. Each disc is 7-10mm thick and there are 24 vertebrae so even a quarter millimeter compression per disc would be significant, cumulatively.

My brother was on a 20 minute blow-down to 600' and everyone was in considerable pain for a few days.

 

[John C. Ratliff]

In the 1970s, I swam down to about fiftz feet, put a butterflz knot in the anchor line for a loop, took off a 16 pound weight belt and put it on the line. I then swam around in Clear Lake, Oregon, completelz weightless.

SeaRat

 

[Wibble]

My brother was on a 20 minute blow-down to 600' and everyone was in considerable pain for a few days.

Technical divers doing deep "bounce" dives (which is the term for all non-saturation dives) will descend as fast as possible in order to maximise bottom time. Don’t hear of this pain phenomenon from them.

 

[Duke Dive Medicine]

Technical divers doing deep "bounce" dives (which is the term for all non-saturation dives) will descend as fast as possible in order to maximise bottom time. Don’t hear of this pain phenomenon from them.

Most tech divers aren't going to 600+ fsw. If you were to interview the ones who do, I'd imagine that at least some of them would report compression arthralgia. It's possible that recreational divers experience them too but don't know what the cause is. We had a nurse who would get compression pains in the chamber when compressing to 33 feet at a rate of 2 feet per minute.

Best regards,
DDM

 

[boulderjohn]

Technical divers doing deep "bounce" dives (which is the term for all non-saturation dives) will descend as fast as possible in order to maximise bottom time.

Technical divers should descend at the rate of their dive plan. Descending more rapidly will make a difference in your planned nitrogen levels. If you are using a computer that is calculating the reality of your dive, it won't make a difference, but if you are following a planned profile, the difference can be significant.