> Decompression sickness only occurs when a person is under elevated pressure for a period of time, and then the pressure is released. Pressurizing the sub could in fact cause the decompression sickness, not prevent it.
Only a too rapid depressurization will cause decompression sickness. Unless the sub is pressurized to a much higher pressure than normal atmospheric pressure, decompression sickness won't be an issue.
According to National geographic (http://news.nationalgeographic.com/news/2012/03/120308-james...) the entire sub is only going to shrink by about 2.5 inches. If we assume that the shrinkage only occurs on the 43 inch pilot sphere, then the lost volume is only about 16% of the total original volume, which means pressure at the bottom is about 120% atmospheric pressure. Since most airplanes are pressurized to 10.9 psi, which is about 75% of atmospheric pressure at sea level (14.9 psi) I don't think decompression sickness will even be an issue.
> For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends.
I googled for James Cameron's website and couldn't find anything. Could you please provide a link?
Yes, obviously an airplane is going to pump air in from somewhere to keep the chamber at a higher pressure than the ambient environment and a submarine with a shrinking chamber is going to remove air to keep the chamber at a lower pressure than the ambient environment. However, both an airplane and a sub are designed to keep a chamber at a specific pressure that is relatively close to normal atmospheric pressure, which prevents humans in the chamber from being at risk for decompression sickness, short of some sort of catastrophic failure.
"I googled for James Cameron's website and couldn't find anything. Could you please provide a link?"
The info is scattered throughout the site.
http://deepseachallenge.com/the-sub/sub-facts/ states:"The pilot is descending about 36,000 feet (10,973 meters), but his ears won’t pop during the journey; the pressure inside the pilot’s sphere stays constant."
Where does it say that air is drawn out of the chamber in order to maintain pressure? All I could see was scrubbing co2 and condensing h20 so that the pilot doesn't die/pass out.
Only a too rapid depressurization will cause decompression sickness. Unless the sub is pressurized to a much higher pressure than normal atmospheric pressure, decompression sickness won't be an issue.
According to National geographic (http://news.nationalgeographic.com/news/2012/03/120308-james...) the entire sub is only going to shrink by about 2.5 inches. If we assume that the shrinkage only occurs on the 43 inch pilot sphere, then the lost volume is only about 16% of the total original volume, which means pressure at the bottom is about 120% atmospheric pressure. Since most airplanes are pressurized to 10.9 psi, which is about 75% of atmospheric pressure at sea level (14.9 psi) I don't think decompression sickness will even be an issue.
> For this sub, during descent the pilot's chamber compresses and air is drawn out of that chamber to keep the pressure constant (this from JC's site). Rather unlike the airplane, into which the air is pumped from the outside, usually from the engine compressor's bleed, to keep the pressure from falling too low as it ascends.
I googled for James Cameron's website and couldn't find anything. Could you please provide a link?
Yes, obviously an airplane is going to pump air in from somewhere to keep the chamber at a higher pressure than the ambient environment and a submarine with a shrinking chamber is going to remove air to keep the chamber at a lower pressure than the ambient environment. However, both an airplane and a sub are designed to keep a chamber at a specific pressure that is relatively close to normal atmospheric pressure, which prevents humans in the chamber from being at risk for decompression sickness, short of some sort of catastrophic failure.