Scuba & Nitrox Glossary: F
Nitrox and breathing-gas terminology is prioritized first. General scuba terms follow below. Definitions are educational summaries and do not replace formal training, manufacturer instructions, or an operational dive plan.
Nitrox & Gas Terms — F
- FiO₂
- Fraction of inspired oxygen; in open-circuit scuba it is closely related to the oxygen fraction of the breathing mix.
- FO₂
- Fraction of oxygen in a gas, expressed as a decimal such as 0.32 or a percentage such as 32%.
- Fill Log
- A record of cylinder identification, pressure, mixture, analysis, date, and responsible personnel.
- Final Analysis
- Gas analysis performed after blending is complete and the mixture has stabilized.
- Flow Restrictor
- A device used to control gas flow during analysis or blending.
- Fill Analysis
- Measuring a completed cylinder fill before accepting or using it.
- Fill Temperature Compensation
- Allowing for pressure change as a recently filled cylinder cools.
- FO2 Verification
- Confirming the actual fraction of oxygen with a calibrated analyzer.
- Fractional Mixing
- Creating a blend by adding measured gas components according to partial pressures.
- Fresh-Gas Flow
- The rate at which breathing gas enters some rebreather loops.
General Scuba Terms — F
- Fin Pivot
- A buoyancy-training exercise used by some instructional systems.
- First Stage
- The regulator component that reduces cylinder pressure to intermediate pressure.
- Free Flow
- Continuous unintended gas flow from a regulator.
- Freediving
- Breath-hold diving without a self-contained breathing apparatus.
- Frog Kick
- A finning technique that directs thrust rearward and can reduce disturbance of the bottom.
- Fin Pivot Exercise
- A training drill used to develop buoyancy control.
- First Stage Freeze
- Regulator icing that can cause free flow in cold water.
- Float Plan
- Information left ashore describing vessel, divers, location, and expected return.
- Flooded Mask
- A mask containing water, intentionally or accidentally.
- Flutter Kick
- A common alternating-leg finning technique.