Glossary of SCUBA Diving - O

O

octopus breathing

Sharing air using an octopus regulator

octopus regulator

also octo reg Further information: Diving regulator#Secondary demand valve (Octopus)

A secondary demand valve fitted to a first stage diving regulator for use as an alternative air source for another diver in case of an emergency.

offshore diver

Colloquial term for a diver who works in the offshore oil and gas industry.

open circuit

Breathing apparatus which discharges exhaled gas into the environment, without any further use.

oro-nasal mask

A breathing mask that covers the mouth and the nose only. It may occur independently, as an oxygen mask, or it may occur inside a full face diving mask or helmet to reduce the amount of dead space

O-ring

A mechanical gasket in the shape of a torus; a loop of elastomer with a circular cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.

outgassing

Further information: Decompression (diving)#Outgassing of tissues

Diffusion of gas out of the tissue into the blood, and transport to the lungs where it diffuses into the lung gas and is eliminated by exhalation.

overweighting

see also diving heavy

Carrying more weight than is necessary to achieve neutral buoyancy at all times in a dive.

oxygen analyzer

Instrument for measuring the partial pressure of oxygen in a gas mixture

oxygen clean

Cleaned for oxygen service by appropriate methods and materials and tested for contaminants.

oxygen clock

Further information: Oxygen toxicity #Underwater

A notional alarm clock, which accumulates hyperbaric oxygen exposure at a rate which increases with higher ppO₂ toward the maximum single exposure limit recommended

oxygen compatible

Made from materials which are suitable for oxygen service.

oxygen compatible air

Air which has been filtered to reduce contaminants to a level suitable for blending with high pressure oxygen.

Oxygen Pete

Mythical monster associated with CNS oxygen toxicity, also CNS oxygen toxicity seizure.

oxygen toxicity

A condition resulting from the harmful effects of breathing molecular oxygen (O₂) at elevated partial pressures.

oxygen window

Inherent unsaturation due to metabolic reduction of total gas pressure in the tissues.