Deepest "dive" in a hyperbaric chamber

In November 1992, French diver Theo Mavrostomos achieved for the deepest dive on dry land. In a hyperbaric chamber – of the sort used to re-acclimatise deep-sea divers to surface pressure and prevent them developing the bends – Mavrostomos survived a pressure equivalent to that 701 m (2,299 ft 10.37 in) beneath the surface of the ocean. Mavrostomos, working with the French company Comex, in Marseilles, was helping to test a new breathing gas for divers – comprising helium, oxygen and hydrogen. The conventional mixture prior to this was a two-component gas, made from helium and oxygen. However, this caused side effects at high pressure such as tremors, memory problems, nausea and dizziness – symptoms known collectively as high-pressure neurological syndrome (HPNS). Breathing oxygen alone at high pressure causes similar symptoms – the "oxygen toxicity" first noted by French physiologist Paul Bert. But adding hydrogen and/or helium, being lighter gases, makes a mixture that’s able to pass in and out of body tissues with minimal disruption.