Dive Terminology

Air time remaining (ATR): The time you may remain at the current depth until an ascent at 9 m/min. (30 ft./min.) would result in surfacing with the reserve pressure.

Central nervous system (CNS): A measure of central nervous system oxygen toxicity caused by exposure to increased partial pressure of oxygen (PO2) while diving.

Closed-circuit rebreather (CCR): A diving mode used for dives performed with a rebreather that recirculates exhaled gas and removes carbon dioxide.

Maximum operating depth (MOD): The greatest depth at which a breathing gas can be used before the partial pressure of oxygen (PO2) exceeds the safe limit.

No decompression limit (NDL): A dive that does not require decompression time while ascending to the surface.

Oxygen toxicity units (OTU): A measure of pulmonary oxygen toxicity caused by exposure to increased partial pressure of oxygen (PO2) while diving. One OTU is equivalent to breathing 100% oxygen at 1 ATM for 1 minute.

Partial pressure of oxygen (PO2): The pressure of the oxygen in the breathing gas, based on depth and oxygen percentage.

Pressure-based surface air consumption (PSAC): The change in pressure over time, normalized to 1 ATM.

Respiratory minute volume (RMV): The change in gas volume at ambient pressure over time.

Surface interval (SI): The amount of time that has elapsed since the completion of the last dive.

Time to surface (TTS): The estimated amount of time it will take to ascend to the surface, including decompression stops.

Volumetric surface air consumption (SAC): The change in gas volume over time, normalized to 1 ATM.