Why Do Deep-Sea Divers Use Helium-Oxygen Mixtures Instead of Compressed Air?

[jmm5872]

Air is dissolved in blood and other bodily fluids. As a deep-sea diver descends, the pressure increases and the concentration of dissolved air in the blood increases. If the diver returns to the surface too quickly, gas bubbles out of solution within the body so rapidly that it can cause a dangerous condition called "the bends." Use Henry's Law to show why divers sometimes use a combination of helium and oxygen in their breathing tanks in place of compressed air.

Henry's Law: P₂ = k₂X₂

Given: Henry' Law constant (k) at 25 degrees celsius:
k_oxygen = 4.34 x 10⁴ atm
k_helium = 1.7 x 10⁵ atm

Partial pressure of Oxygen in air at normal conditions: .209 atm
Partial pressure of Helium in air at normal conditions: 5 x 10^-6 atm


I don't think we need the partial pressure in air since the compressed air is being replaced with Oxygen and Helium combination.

This seems like more of a conceptual question and I don't really understand where to start. I know Henry's Law has to do with the carbonation of soda as well. An increase of pressure above the solution will increase the amount of solute dissolved, and a sudden decrease in pressure will cause the gas to bubble out of the solution.

I also know that the henry's constant of helium is higher than that of oxygen so the vapor pressure of helium would also be higher. Does this simply mean that because the vapor pressure of helium is higher than that of oxygen, or compressed air for that matter, that it will be harder to dissolve in the blood and therefore less likely to bubble back out?

 

[Borek]

Helium use has nothing to do with the bends, no idea what the question really is about.