[6] Although the first reported use of hydrogen seems to be Antoine Lavoisier (1743–1794) experimenting on guinea pigs, the actual first uses of this gas in diving are usually attributed to trials by the Swedish engineer, Arne Zetterström in 1945.
[7] Comex subsequently developed procedures allowing dives between 500 and 700 m (1,640 and 2,297 ft) in depth, while breathing gas mixtures based on hydrogen, called hydrox (hydrogen-oxygen) or hydreliox (hydrogen-helium-oxygen).
The memorial dives were performed using the same breathing mixture of 96% hydrogen and 4% oxygen as was developed and tested by Zetterström in the 1940s.
[9] A 230 m hydrox dive in the Pearse Resurgence in New Zealand was made on 14 February 2023 by Richard Harris, using a Megalodon rebreather.
[6] Hydrox may be used for combating high pressure nervous syndrome (HPNS), commonly occurring during very deep bounce dives.