Oxygen window in technical diving

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1 Background
2 Application
3 Notes
4 References
5 External Links

The oxygen window is ^[1] the difference between the partial pressure of oxygen (ppO₂) in body tissues and the ppO₂ in the gas breathed. It is caused by metabolic consumption of oxygen.

[edit] Background

The effects of using oxygen to increase decompression efficiency in technical diving are well known and widely applied; but many of the practical consequences and benefits still need extensive research. Decompression in diving is still far from being an exact science, and divers when diving deep must make many decisions based on personal experience rather than scientific knowledge.

In technical diving, allowing for the oxygen window effect increases decompression efficiency, thus allowing shorter decompression stops when using decompression gases with high ppO₂. Reducing decompression time is important to reduce time spent at shallow depths in open water (avoiding dangers such as water currents and boat traffic), and to reduce the physical stress imposed on the diver.

[edit] Application

Technical divers commonly use the oxygen window to make decompression more efficient. This is done by using gas mixes with high ppO₂ in some segments of the decompression schedule. As an example, a popular decompression gas is 50% nitrox on decompression stops starting at 21 meters.

Where to add the high ppO₂ gas in the schedule depends on what limits of ppO₂ are accepted as safe, and on the diver's opinion on the level of added efficiency. Many technical divers have chosen to lengthen the decompression stops where ppO₂ is high and to push gradient at the shallower depths of the decompression curve, thus creating an S-shaped curve.

Nevertheless, much is still unknown about how long this extension should be and the level of decompression efficiency gained. At least three variables of decompression are relevant in discussing how long high ppO₂ decompression stops should be:

Time needed for circulation and disposal of gas through the lungs
The vaso-constrictive (reduction of the size of blood vessels) effects of oxygen, reducing decompression efficiency when blood vessels start contracting
The relative threshold where the body starts on-gassing rather than off-gassing.