Dive Rite O2ptima Owner's Manual download pdf (Page 37)

O ptima FX Owner’s Manual

Ch. 5 Pg. 1

Chapter 4

Dive Planning and Procedures

Oxygen

Oxygen is the gas that sustains life, but the oxygen dosage must fall within a specific range in

order to sustain life. Too little leads to unconsciousness and eventually death, and too much

causes respiratory and central nervous system issues. The term used to describe the amount of

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Oxygen present in the breathing mixture is “partial pressure dosage” or PO . The PO value

is obtained by multiplying the O % in the mixture by the total pressure. The units of

pressure quantifying the dosage are ata or bar. The percentage of oxygen in a breathing mix is

not the critical factor, the critical factor is the partial pressure of oxygen that is being inspired.

It is imperative that the concept of partial pressure be well understood in order to safely use

rebreathers. If you are unsure about any aspects of this concept please review with your

instructor before continuing.

At standard atmospheric pressure, it is possible to have partial pressures of Oxygen range

between 0 and 1.0 ata because we could vary the % of O between 0% and 100%. The

percentage of oxygen in the atmosphere is approximately 21% and does not vary with altitude,

but the PO does change with altitude. At sea-level that means the normal exposure is 0.21ata,

this is called normoxic exposure. Our bodies can still perform work with a PO down to about

0 .16ata (this occurs at approximately 7500 feet/ 2300m above sea level), below this our bodies

enter a hypoxic state.

Hypoxia is the condition where there is insufficient Oxygen to sustain normal activity. If

asleep or at rest, life could continue. Around 0.1 ata, there is not enough Oxygen to sustain life

- death is the eventual result from anoxia. Anoxia is the condition where there is insufficient

Oxygen at the cellular level to sustain life.

The opposite of hypoxia is hyperoxia where there is a greater oxygen exposure than normal.

Hyperoxia can result in a condition called Oxygen toxicity which results from breathing a

hyperoxic gas for an excessive period of time. By exceeding the limits of Oxygen, the bodies

compensating mechanisms have been exhausted. This results in several symptoms that may

occur in any order and without progressively increasing severity.

These exposure limits have been determined over time. The greater the dosage the lower the

allowable duration. Due to the length of the dives typically performed on rebreathers and the

typical scrubber duration, most rebreather divers limit the working exposure to a max 1.3ata.

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Dive Rite O2ptima Owner's Manual Page 37