Dalton's law refers to the effects which partial pressure
might have on divers. This law says that the pressure of mixed gases is
equal to the pressure produced by the individual gas. It can also be
explained by saying that the total pressure of a mixture of gases
equals the sum of the partial pressures of gases which are part of it.

This means that the number of molecules present in the total
volume of a gas is proportional to the number of molecules present on
each one of the gases which compose it. This way, while the total gas
pressure increases as a diver goes deeper into the water, the partial
pressure of each gas involved increases as well, and the effects which
might cause on the divers body also increases with it.

For example, air is a mixture of gases which contains about
80% of nitrogen and 20% of oxygen although it also includes small
amounts of other gases as well. According to Dalton's law, the partial
pressure exerted by the nitrogen and by the oxygen which make the air
will be equal to the total pressure of the air; and they will increase
simultaneously.

A specific case in which the effects specified by Dalton's law
should be seriously considered by divers is regarding nitrogen.
Whenever there is an increase of the partial pressure of nitrogen, this
would cause a higher nitrogen concentration dissolved in the diver's
blood, and this could cause him to suffer a nitrogen narcosis. This,
among many other situations which might arise due to the facts stated
by Dalton’s law, should be prevented by a proper planning of the diving
activities which a diver intends to practice.

The effects which a gas might cause on a diver are based on
the pressure which such gas exerts on his body. This explains why
Dalton's law is so important for divers and why they should understand
it and prevent the effects it explains. Partial pressure related
problems can affect the human body in several ways, such as causing
nitrogen narcosis or ear canal damage among others, and therefore
divers should pay attention to these dangers and take the necessary
precautions.