Nitrogen narcosis

Nitrogen narcosis is a problem for underwater divers. It affects the brain and nervous system a lot like alcohol, but goes away when the diver rises to a shallower depth. It does not have lasting effects after the depth is reduced.
Who can get it.
Any underwater diver who goes deeper than 30 m (100 ft)while breathing air, or any time when the pressure of nitrogen in the breathing gas is more than about 3,2 bar.
How to prevent it.
It only happens when the pressure of nitrogen is high. If the pressure is kept low by staying at a shallower depth it will not happen. If the breathing gas has less nitrogen it will only start at a deeper depth. Helium gas can be used in place of nitrogen in breathing gas for divers to make it less likely to have nitrogen narcosis.
What actually happens.
The nitrogen gas dissolved in the diver affects the working of nerve cells. At higher pressures more nitrogen can be dissolved.
It starts off as a mild effect like being slightly drunk, but as the pressure increases it gets more serious, like getting more drunk. Eventually the diver may lose consciousness.
Why is it a problem.
A diver who has nitrogen narcosis will have slower reactions and may not think clearly. If something goes wrong the diver may not be able to cope with the problem. This can be dangerous.
What to do about it.
The diver can move to a shallower depth or change to a different breathing gas with less nitrogen. This will usually be a mixture containing helium.