Most of the pressure you get from deep sea diving is due to the water. Depth into the Earth doesn't have you under water, so the pressure increase is going to be much more mild.
At sea level the pressure is 1 atm (atmosphere), you are carrying a column of air the height of the entire atmosphere (= 1.0332 kg per square centimeter). As you know water weighs approximately 1 gram per cubic centimeter. So the pressure of a column of water on a square centimeter is a 100 grams per meter of the column. So a ten meter column (100 gram * 10 = 1 kg) exerts approximately the same pressure as the entire atmosphere does on a square centimeter.
The pressure increases by one atmosphere for every ten feet of water above you. As you can see, pressure increases rapidly as you descend in death. You need about 11km (11,000 meters) of earth air to equal 75% of an atmosphere. In other words, to have the pressure at sea level doubled by air, you need 22km of air above you. Going 4km down in a mine is only going to mean 15km of air is above you. With water, you need to only go 10 feet (3m) to double the pressure! To get that sort of pressure from air, you would need a mine that was as deep as one and a half Mount Everests. Typically, decompression stops are only made if you spend time below 40 feet, or 4x atmospheres. I think. It's been awhile since I've done PADI. 4x atmosphere would require something like 50km of mine shaft, which would put you well into the earth's mantle.
Do you have to be a mammal to get the bends? Is it possible that this may be a reason why whales beqach? Something chased them to the surface or Navy sonar bothered them?
Yes, or an amphibious creature like a turtle. You have to breath "air", not collect oxygen from water via gills.
Nah. You just need dissolved gases in your system to boil out when the pressure changes. PV = nRT, right? If nRT are all constant, and P goes down, then V must go up. Is that Boyle's Law? Most fish have swim bladders, which expand and kill them. If you've ever pulled any deep sea fish up, you'll often find their guts protruding from their mouths. This is due to the swim bladder pushing their insides to the outside. Deep sea bycatch, thrown back either because no one wants it or because the government won't let you keep it (fish is too small, wrong species, etc), typically dies anyway because of this. In fact, deep sea fish are extremely sensitive to changes in pressure, as going from 100 atm to 101 or 99 atm isn't as big a change as going from 2 atm to 1 atm or 2 atm.
Well, I guess I assumed Orleander was talking about the Bends strictly -- not death due to massive internal hemmoraging due to the pressure change. And most creatures that live at depth tend to stay around that depth, correct? Only mammals really take a breath of air, then dive to several thousand feet before returning to the surface (or in the case of humans, construct equipment that allows us to breathe air while under water).
Isn't the Bends caused by a change in pressure resulting in dissolved gases turning back into gases? Fish already have dissolved gases in them, and by lowering pressure, the gas comes out. Like opening a can of soda. Soda's made by putting water and CO2 under pressure, which means more CO2 gets dissolved. When you open the can, the pressure decreases, and bubbles form. In mathematical terms: P1V1=P2V2 So a fish at P1 = 100 atm with V1 = 1 (its body)brought up to P= 1 atm is going to have some problems with its V2. [edit] Doh. That's Boyle's law, which is wrong. It's Henry's Law: p= k*c, where p = partial pressure of solute, c = concentration of solute, and k is a constant. So p1 = k*c. At p1 = 100 atm, c1 = 1. If brought up to p2 = 1 atm, then c2 = 1/100. As the pressure decreases, the concentration of dissolved solute will come out as a gas.
As someone else explained, there's no increase in pressure if you're going down into air; it has to be water. That's because water is much heavier than air. Turtles are not amphibians, they are aquatic reptiles like alligators and sea snakes. They have only lungs to breathe with. Amphibians such as frogs and salamanders have both lungs and gills.
I didn't say they were amphibians, I said they were amphibious. I was using the generic definition of the word. Adult amphibians don't have gills either, only the "larval" stages do.
