Henry's Law

The higher the partial pressure of the gas on the liquid, the more gas will dissolve into the liquid until a state of equilibrium is achieved. This means that if a quantity of gas dissolves at 1 atm, then three quantities of that same gas mixture will dissolve at 3 atm. In the human body this gas exchange occurs between the respiratory system and bloodstream. Henry’s Law describes how the amount of dissolved gas in a liquid is directly proportional to its partial pressure upon the liquid.

As a diver descends in-gassing occurs, and the gases a diver breathes will begin to pass into solution in the body’s various tissues. As depth and dive time increases, the level of gases dissolved in the body increases. On ascent, this process begins to reverse and a diver will begin off-gassing the elevated gasses. That is why ascending at a maximum rate of 30 ft. per min. and a precautionary “safety stop” are essential when diving. Ascending slowly enables the dissolved gases to be carried to the lungs by the bloodstream and pass out of solution on exhalation.