Nitrogen is colorless, odorless, and tasteless, and we breathe more of it each day than any other element — including oxygen. Indeed, it makes up more than 70% of the Earth’s atmosphere. But beneath the waves, it can be life-threatening: at deep depths, it can cause nitrogen narcosis, a debilitating loss of function similar to intoxication. And if a diver ascends too rapidly, the pressure change can cause nitrogen to bubble out of the blood, causing extreme pain, paralysis and sometimes death — a condition commonly known as the bends. Helium isn’t absorbed by the blood in the same way as nitrogen, and while it can still cause the bends it doesn’t cause narcosis and is generally preferred for deepwater technical diving.