In the early part of the 20th century, American physicist and chemist, Professor Elihu Thomson – the person credited with putting the eventual use of helium on the diving menu – had originally proposed the use of hydrogen as a suitable replacement for nitrogen in the breathing mix used by divers.
The advantages of hydrogen over helium are enormous. Hydrogen is half the atomic weight of helium, less dense, more readily available and far cheaper. However, on the down side it’s also highly flammable, and requires great care in its use; a fact highlighted by the 1937 ‘Hindenberg’ disaster when the world’s most luxurious airship – a ‘lighter-than-air’ passenger aircraft that halved the time taken by the trans-Atlantic ocean liners traveling between Europe and America – burst into flames, killing 37 of its passengers, when an electrostatic discharge from a securing line ignited escaping hydrogen during landing.
Nevertheless, while the use of hydrogen for Airships and Zeppelins came into question, the attractions of hydrogen as an alternative replacement for nitrogen in a diver’s breathing mix continued to encourage research into its use. Austrian Physiologist and Physician, Hermann von Schrötter (1870 – 1928) – a pioneer of aviation and hyperbaric medicine who made important contributions in the study of decompression sickness – conducted experiments in the use of hydrogen, as did Swedish researcher, Arne Zetterstrom.
Conducting research into the use of Hydrox mixtures for the Swedish Navy, Zetterstrom made a series of dives in 1943 – 1944 – the deepest to 160-metres, using a mix of 96% hydrogen and 4% oxygen – before his untimely death, in 1945, in a diving accident un-related to his use of hydrogen in the breathing mix. Professor J.B.S. Haldane (son of J.S Haldane) also toyed with the idea of using Hydrogen and oxygen mixtures and the theoretical advantage offered by the lighter gas in decompression research.
In 1988 four divers from the French diving company, Comex (Compagnie Maritime d’Expertise) and two French Navy divers spent eight days in a chamber that was gradually being pressurised to a depth equivalent to 53 times that at the surface. The capsule was lowered to depth in the Mediterranean Sea, off Marseilles, where the divers – breathing a gas consisting of 49% Hydrogen; 50% Helium, and 1% Oxygen – took it in turns to exit the chamber on an umbilical hose, spending a total of 28-hours working on pipeline connection exercises at a depth of 534-metres (1,752 feet). The return to surface pressure took an additional eighteen days. A depth that highlighted the limiting factors to working at depth; namely:
High-Pressure Nervous Syndrome (HPNS): manifesting itself at around 200-metres, the effects increase with depth and impair the diver’s efficiency.
Gas Density: the effort of moving the gas into and out of the lungs, reduces the diver’s efficiency.
Fatigue: accentuated by lengthy periods of saturation.
In 1992, Comex divers set a new depth record with an experimental dry-dive – in a pressurised chamber – to a simulated depth of 701-metres (2,300 feet) for seven hours, but required twenty-four days of decompression.