Scuba & Nitrox Glossary: P
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 — P
- Partial Pressure
- The pressure contributed by one gas in a mixture; calculated as gas fraction multiplied by absolute pressure.
- Partial-Pressure Blending
- Creating a mixture by adding measured amounts of individual gases to a cylinder.
- PPO₂ or PO₂
- Partial pressure of oxygen.
- Pulmonary Oxygen Toxicity
- Lung irritation or injury associated with prolonged elevated oxygen exposure.
- Pre-Breathe
- Breathing a selected gas before a phase of a dive; the term is procedure-specific and not a substitute for correct gas verification.
- Panel Blending
- Controlling gas sources through a dedicated blending manifold or panel.
- PO2 Setpoint
- The target oxygen partial pressure maintained by a closed-circuit rebreather.
- Pre-Breathe Check
- A timed rebreather check used to verify function before entering the water.
- Premixed Nitrox
- Enriched air produced and stored before individual cylinder filling.
- Pressure-Blending Worksheet
- A calculation record specifying component pressures for a target blend.
General Scuba Terms — P
- Panic
- An uncontrolled stress response that can impair judgment and action.
- Pony Bottle
- A small independent bailout cylinder.
- Pressure Group
- A repetitive-dive table designation representing estimated residual nitrogen.
- Primary Regulator
- The second stage normally breathed by a diver.
- Profile
- A record or plan of depth versus time.
- PSI
- Pounds per square inch, an imperial pressure unit.
- Panic Cycle
- Escalating stress and ineffective actions that can lead to loss of control.
- Permanent Mooring
- A fixed anchoring system installed to reduce repeated anchor damage.
- Independent Pony Cylinder
- A small independent cylinder carried as an alternate gas source.
- Positive Entry
- An entry made while positively buoyant, normally remaining at the surface.
- Post-Dive Check
- A review of team condition, equipment, gas, and any unusual events after surfacing.