FN₂ — Fraction of Nitrogen

FN2 is the portion of nitrogen within a specific gas mixture. This value tells you exactly how much nitrogen you breathe at depth. Divers use this number to calculate nitrogen absorption rates during a dive. For example, air has an FN2 of 79% because it contains 21% oxygen and 79% nitrogen. If you switch to Nitrox 32 in 2024, your FN2 drops to 68%. This change allows for longer bottom times because your body absorbs nitrogen more slowly. Many beginners forget to recalculate their deco limits when they use different mixes. Always verify your gas math before you descend below 18 m. A mistake here leads to DCS.