Dalton’s Law

15.02.2017 by Felix Wiesel

Dalton’s Law is one of the most important laws of physics for divers. It deals namely with the pressure of gas mixtures. Since pressure increases under water, this also affects the diver’s breathing air.

What does Dalton’s Law say?

According to Dalton, the total pressure of a gas mixture is composed of the individual pressure of the gases which are contained in it. Conversely it can be deduced that the individual pressure of a gas corresponds to its volume share in the gas mixture.

Our breathing air is made of nitrogen, oxygen, carbon dioxide and a small percentage of inert gases. Now if the pressure increases under water, the pressure of the individual gases also rises. In itself this is not dangerous, but particularly for deep diving though, this is important.

Oxygen can harm human beings at a pressure of about 1.7 bar. The critical limit of oxygen pressure is achieved as of a diving depth of around 71 metres according to Dalton’s Law – provided that you use breathing air to dive. With pure oxygen, humans could only dive up to about 7 metres.

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