Dalton's Law (partial pressures)

Dalton’s Law states that the total pressure of a gas mixture is the sum of its individual parts. It is basic physics. This principle dictates how much oxygen or nitrogen you actually breathe at depth. At 30 m in Koh Tao, the total pressure is 4 bar. Since air contains 21% oxygen, your partial pressure of oxygen (PO2) becomes 0.84 bar. This calculation is vital for avoiding oxygen toxicity during deep dives. If your PO2 exceeds 1.4 bar, you face serious seizure risks. Many divers forget this when switching to nitrox. Always check your computer settings before you descend. A small math error can be fatal.