Question

In modern diving apparatus, a mixture of Helium and oxygen gas is used. Why?

Answer 1

As dive depth increases, ambient pressure increases-increasing the divers exposure to breathing gases. For this reason it will generally become increasingly narcotic, the deep we move towards the bed of the sea.

Complete step-by-step answer:
-We add helium to the breathing mix to reduce the proportions of nitrogen and oxygen below those of air, so that to allow the gas mix to be breathed safely on deep dives.
-At depth, Nitrogen from air is absorbed into the tissues and blood.As we come up from depth and the pressure reduces, the Nitrogen expands forming the bubbles in the blood known as ‘the bends.’
-Helium like Nitrogen is inert but it is also a ‘smart-gas’ with smaller molecules than Nitrogen. It is because it is not used to break down in the body to provide energy.
-If a mix of Oxygen and Helium is breathed at depth, as the pressure reduces at upwards, the Helium cleverly escapes from the body’s tissues reducing the probability of forming bubbles and causing the bends.
-A very low quantity of nitrogen is required to reduce nitrogen narcosis and other physiological effects of the gas at depth.
-This decrease of nitrogen causes this disease called bends.

Note: When sea divers dive deep into the sea, due to an increase in pressure, a large amount of nitrogen dissolves in their blood. The solubility of nitrogen decreases at the surface and it separates from the blood and forms small air bubbles,and thus, leads to a condition called bends, DCS (Decompression Sickness).