You cannot receive any oxygen if you simply breathe inert gas. Deep divers may use a combination of oxygen and helium to avoid the "bends" in some instances. The bends occur when divers ascend too rapidly, causing dissolved nitrogen to form bubbles in their blood and cause embolisms. To prevent this, they are given an initial dose of oxygen at high pressure so that it enters their bloodstream before they go down again. Oxygen is vital for life because it reacts with hydrogen molecules to form water, which is essential for living organisms. Without oxygen, humans would die within minutes. However, due to its reactivity, much of the oxygen we breathe in is lost through exhalation. This is why airliners need to constantly pump pure oxygen into the passenger cabin from outside sources - otherwise everyone would die! The most common source of oxygen for deep divers is compressed air, but they can also use nitrox (80% oxygen + 20% nitrogen) or heliox (hydrogen oxide, a mixture of oxygen and helium). These gases are mixed on site by equipment called compressors. They work by taking ambient air and pushing it through metal plates coated with titanium or platinum which absorbs the carbon dioxide while letting out harmless nitrogen and other gases. The divers can then breathe these purified gases instead. Deep diving brings with it many risks not present in shallow diving. The pressures involved can burst blood vessels or even damage the brain.