How deep can a scuba diver go on compressed air?

Answer 1

If the gas is normal air (~20-22% oxygen), the maximum recommended depth of most dive organisations is in the region of 50-60m. The reason for this is that the deeper you go, the higher the pressure of the water. For example, on the surface, the pressure is 1 bar, 10m is 2 bar, 20m is 3 bar 30m is 4 bar etc.

Oxygen becomes toxic to the human body at about 1.6 bar so if you are at 70m, with a mix of 20% oxygen, you are at 8 bar of pressure. At 8 bar, the parital pressure of oxygen is 1.6 bar, enough to become toxic. So compressed air becomes dangerous at 70m so most organisations advise to go no deeper than 50-60m.

If you use a different gas blend, such as Nitrox ar Trimix, the amount of oxygen is different so the depths are different too.

In summary, on compressed air, the maximum is about 70m, recommended 50-60m max.

Answer 2

The deepest dive with Scuba breathing air is recorded as 155M by Dan Manion in 1994, although the safe limit is usually described as about 50M by diving training bodies such as BSAC, although most recognise this requires special training. Nitrogen narcosis can make deep diving very dangerous and other risks like decompression sickness increase with depth. At extreme depth oxygen can become poisonous.