Question

why sea divers use helium

Answer 1

The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen below those of air, to allow the gas mix to be breathed safely on deep dives. A lower proportion of nitrogen is required to reduce nitrogen narcosis and other physiological effects of the gas at depth.

Answer 2

because it is the lightest gas and have more denaity compare to other gasses