At what depth is it recommended to use 100 percent oxygen?

Using 100 percent oxygen is recommended at depths of up to 6 m (20 ft) because at this shallow depth, the partial pressure of oxygen remains at safe levels for recreational diving. Oxygen becomes toxic when its partial pressure exceeds certain limits, which can occur at deeper depths.

At 6 m, the partial pressure of oxygen is about 1.2 ATA (atmospheres absolute), which is generally considered safe for breathing 100 percent oxygen. This allows divers to benefit from the advantages of oxygen, such as improved visibility and accelerated off-gassing of nitrogen, without the risk of oxygen toxicity that increases with depth.

In contrast, using 100 percent oxygen at depths greater than this, as suggested by the other choices, can lead to oxygen toxicity, increasing the risk of serious neurological and pulmonary issues. Therefore, it's crucial to adhere to the depth limitation to ensure diver safety while utilizing pure oxygen.