Lung Volume During Ascent: Boyle's Law in Diving

As a diver ascends, water pressure decreases → gas in lungs expands (Boyle's Law: P₁V₁ = P₂V₂ at constant temperature).

Physics

• At 10 m (2 ATA): Lung volume = 1/2 surface volume.
• At surface (1 ATA): Volume doubles from 10 m.
• Rapid ascent → overexpansion → pulmonary barotrauma (pneumothorax, mediastinal emphysema, arterial gas embolism).

Critical Rule

Never hold your breath during ascent. Continuous exhalation allows expanding gas to escape.

Practical Application

• Ascend slowly (≤9–10 m/min / 30 ft/min).
• Safety stop (3–5 min at 5 m / 15 ft) for off-gassing.
• Breathe normally; don't skip breathing.

Same principle applies to any gas-filled space (sinuses, ears, GI tract, BCD, dry suit). Equalize on descent; vent on ascent.