from wiki
Scuba divers and submariners also rely on artificially-delivered O2, but most often use normal pressure, and/or mixtures of oxygen and air. Pure or nearly pure O2 use in diving at higher-than-sea-level pressures is usually limited to rebreather, decompression, or emergency treatment use at relatively shallow depths (~ 6 meters depth, or less).[77][78] Deeper diving requires significant dilution of O2 with other gases, such as nitrogen or helium, to help prevent oxygen toxicity.[77]
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