WWII Points To Ponder

[cyberia]

Germany’s power grid was much more vulnerable than realized. One estimate is that if just 1% of the bombs dropped on German industry had instead been dropped on power plants, German industry would have collapsed and Allied air losses over Europe could have been greatly reduced.

[cyberia]

An unspecified number of air crewmen died in World War II from complications due to extreme gastric pressure. Altitudes up to and beyond 20,000 ft. in unpressurized aircraft causes intestinal gas to expand 300%.

[McCoy]

Originally Posted by cyberia

An unspecified number of air crewmen died in World War II from complications due to extreme gastric pressure. Altitudes up to and beyond 20,000 ft. in unpressurized aircraft causes intestinal gas to expand 300%.

Ouch! What a painful death that must be.

[cyberia]

Originally Posted by McCoy

Ouch! What a painful death that must be.

I wonder about the validity of some of these things. Jim's a doctor, maybe he can shed some light on this claim?

[Jim O]

Originally Posted by cyberia

I wonder about the validity of some of these things. Jim's a doctor, maybe he can shed some light on this claim?

I doubt it. Note that the number was "unspecified". Think about it this way. When a diver goes down and adjusts to deep water pressures that are extremely high, so should the gas in his gut. When he comes up too fast he can get decompression sickness, known as "the bends". At higher pressure more gas can be dissolved in a liquid than at lower pressures and so in decompression sickness oxygen and (mostly) nitrogen bubble out of the blood and into tissue and vessels causing muscle pain and other symtoms. Gas is not known to rupture the gut in decompression sickness (though rupture can occur from high pressures during a dive if it is trapped in a "pocket", this is rare). The gut is an open tube and the gas generally expands and the person passes gas from above or below if needed.

Going from sea level to 30,000 feet involves significant decrease in pressure but not even close to the order of magnitude of coming up to sea level from a deep dive. At 10 meters under water, the pressure on the body is already twice that of air at sea level, three times at 20 meters, four times at 30 meters, etc. At 30,000 feet it is roughly one-third of atmospheric pressure. That's why air crews on these unpressurized planes did not get decompression sickness even with rapid climbs. The change was not that great, from a physiological point of view.

[cyberia]

Originally Posted by Jim O

I doubt it. Note that the number was "unspecified". Think about it this way. When a diver goes down and adjusts to deep water pressures that are extremely high, so should the gas in his gut. When he comes up too fast he can get decompression sickness, known as "the bends". At higher pressure more gas can be dissolved in a liquid than at lower pressures and so in decompression sickness oxygen and (mostly) nitrogen bubble out of the blood and into tissue and vessels causing muscle pain and other symtoms. Gas is not known to rupture the gut in decompression sickness (though rupture can occur from high pressures during a dive if it is trapped in a "pocket", this is rare). The gut is an open tube and the gas generally expands and the person passes gas from above or below if needed.

Going from sea level to 30,000 feet involves significant decrease in pressure but not even close to the order of magnitude of coming up to sea level from a deep dive. At 10 meters under water, the pressure on the body is already twice that of air at sea level, three times at 20 meters, four times at 30 meters, etc. At 30,000 feet it is roughly one-third of atmospheric pressure. That's why air crews on these unpressurized planes did not get decompression sickness even with rapid climbs. The change was not that great, from a physiological point of view.

That settles that. Thanks Jim!

[Wolster]

I am not a Doctor but could the pressure make an exsiting condition worse, such as the appendix? Maybe this could be what it refers to??

[Jim O]

If someone had appendicitis and the entrance to the appendix was blocked, then the increased pressure from the gas inside what would then be a closed space with a narrowed, weakened wall, could well precipitate rupture. But that is a situation where it's going to rupture soon anyway. Generally people at that stage of appendicitis are pretty sick and are not going up in a high altitude bomber.

[cyberia]

Jim, is that 300% expansion rate correct? Sounds over the top to me, but I have nothing to confirm or dismiss it.

[Jim O]

Originally Posted by cyberia

Jim, is that 300% expansion rate correct? Sounds over the top to me, but I have nothing to confirm or dismiss it.

More or less. If the temperature is constant (which it isn't in this system as the temperature at high altitudes is generally much lower) then Boyle's law tells us that Pressure x Volume is constant. So if the pressure is reduced to one third of its original value then the volume will triple. The problem is that the temperature also goes down at the altitude, and lower temperatures cause the Pressure x Volume constant to decrease as well.

The combined gas law is as follows:

84ac3c18f6ab47f5085ddb5b8d62d760.png
where P=Pressure, V=Volume, and T=Temperature.

In an unpressurized cabin, pressure goes down, causing volume of gas inside a hollow viscous like the gut to go up. But the reduced temperature mitigates that effect some.

Where's P-D when we need him? He could explain this a lot better than I can.