Why Do Scuba Divers Need Oxygen Tanks Despite Air Being Dissolved in Water?

[Serj]

Why do scuba divers need oxygen tanks if air is already dissolved in the water? Why can't they just undissolve the trapped gas like when you shake up a bottle of carbonated soda?

 

[Borek]

Soda bottle is oversaturated (once opened). Partial pressure of oxygen in water is too low in normal conditions for the oxygen to be easily taken out from the water. But IIRC it is done on the submerged submarines.

 

[ravenprp]

Scuba divers need oxygen tanks because the air that is dissolved in water is not enough to sustain their breathing needs. While it is true that oxygen is present in water, it is not in a high enough concentration for the human body to use for respiration. In fact, the oxygen in water is only about 3-5% of the total volume. This is why scuba divers need to bring their own supply of compressed air in the form of oxygen tanks.

Additionally, the process of shaking up a bottle of carbonated soda is not applicable to dissolving oxygen in water. Carbonated soda contains carbon dioxide gas, which is forced into the liquid under high pressure. When the bottle is opened, the pressure decreases and the gas is released, causing the bubbles we see. However, oxygen does not dissolve in water under pressure like carbon dioxide does in soda. Instead, it dissolves through diffusion, which is a much slower process.

In summary, scuba divers need oxygen tanks because the air dissolved in water is not enough to sustain their breathing needs, and oxygen does not dissolve in water under pressure like carbon dioxide does in soda. Therefore, bringing their own supply of compressed air is necessary for their safety and survival while diving.