Henry's Law — What It Is and Why It Matters
Henry's law states that the amount of gas that dissolves in a liquid is proportional to the partial pressure of that gas above the liquid. In diving, this means that as you descend and the partial pressure of nitrogen increases, more nitrogen dissolves into your blood and tissues. When you ascend and pressure decreases, that dissolved nitrogen must come back out of solution — ideally slowly and safely.
Henry's law is the fundamental principle behind decompression theory. If you ascend too fast, nitrogen comes out of solution rapidly and forms bubbles — this is decompression sickness. Your dive computer's algorithm models this gas dissolution and release across multiple tissue compartments to keep you within safe limits.
Frequently Asked Questions
Why does nitrogen dissolve in blood but not cause problems at the surface?
At the surface (1 ATA), nitrogen is dissolved in your tissues at equilibrium. The problem arises during diving because increased pressure forces much more nitrogen into solution. On ascent, if pressure drops faster than nitrogen can safely diffuse out, bubbles form — like uncapping a shaken soda bottle.
How does Henry's law connect to decompression stops?
Decompression stops hold you at intermediate depths long enough for excess dissolved nitrogen to diffuse out of your tissues through normal circulation and respiration, at a controlled rate that prevents bubble formation. Each stop reduces the pressure differential gradually.
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