A SCUBA diver experiences severe joint pain upon rapid ascent to the surface. This phenomenon is explained by which gas law?

• A. Henry's Law
• B. Boyle's Law
• C. Dalton's Law
• D. Charles' Law

Answer: (A)

Joint pain after a rapid ascent is due to nitrogen gas coming out of solution in the body's tissues when ambient pressure drops. Henry's Law states that the amount of a gas dissolved in a liquid is proportional to the partial pressure of that gas in contact with the liquid. Under deep-water pressure, nitrogen dissolves in tissues. When ascent is rapid, the surrounding pressure falls quickly, so the dissolved nitrogen becomes supersaturated and forms gas bubbles in joints and tissues—producing the severe pains experienced. This direct link between pressure and gas solubility is why Henry's Law explains decompression sickness. Other laws describe related but different ideas—like how gas volume changes with pressure (Boyle's Law) or how temperature affects volume (Charles'), or how partial pressures add up (Dalton's Law)—but they don't capture why dissolved nitrogen emerges as bubbles during a fast ascent.