When a diver ascends too quickly, a significant risk is the rupture of alveoli due to expanding air. As a diver goes deeper underwater, the pressure affects the volume of gases in the lungs according to Boyle's Law, which states that gas volume decreases under increased pressure and increases under decreased pressure. During ascent, as the external pressure decreases, the gases within the lungs expand. If a diver ascends too rapidly, the rapidly expanding air can exceed the capacity of the alveoli (the tiny air sacs in the lungs), leading to barotrauma, which is the rupture of these alveoli. This condition can result in serious complications such as air embolism, where air bubbles enter the bloodstream, leading to life-threatening situations.
This physiological response highlights the importance of controlled ascension while diving, where divers are trained to ascend slowly to allow for proper equilibration of pressure, thus avoiding such injuries to the lungs.