Helium: how a rare gas opened the deep

Divers breathing air at depth become narcotic. By 40 or 50 metres, judgement and memory degrade, sometimes badly. The obvious fix is to replace some of the nitrogen with a gas that doesn't cause narcosis. Helium was the answer, but it took most of a century to get from laboratory to everyday dive.

The first helium dives

In December 1937, Max Gene Nohl dived to about 420 feet, 128 metres, in Lake Michigan. He breathed a helium-oxygen mix in a self-contained suit he'd developed with physician Edgar End. It was a remarkable dive for its time, and it showed that helium could take divers far beyond what air allowed.

Two years later, in 1939, the US Navy submarine Squalus sank off New Hampshire. Survivors were rescued with a diving bell, and salvage divers working on the wreck used heliox. It was one of the first major operational uses of helium in diving.

Keller and the secret mixes

In the early 1960s, Swiss mathematician Hannes Keller worked with Albert Bühlmann on decompression schedules for deep dives using gas switches. Keller kept his mixes secret. In 1962 he attempted a 1,000-foot bell dive off California. Keller survived, but his companion Peter Small died, and a support diver, Chris Whittaker, was lost during the operation.

The tragedy underlined how little was understood about very deep dives, and how much was riding on calculations nobody could yet check.

Navies, oil and saturation

From the late 1950s, navies and the offshore oil industry drove deep diving research. Saturation diving, where divers live under pressure for days or weeks, was developed in this period, and helium mixes became standard for commercial work.

Deep helium diving also revealed a new problem: high-pressure nervous syndrome, a set of neurological effects including tremors that appears on fast compression to great depths. Helium solved narcosis but not everything.

Helium for everyone

In the 1980s and 90s, cave and wreck divers began using trimix, a blend of oxygen, helium and nitrogen, on open-circuit scuba. Training agencies built mixed-gas courses, and gas blending at dive shops made helium available to civilian divers.

Adding nitrogen back into the mix was partly a matter of cost, as helium is expensive, and partly practical: some nitrogen reduces the problems seen on pure heliox at depth.

The trade-offs today

• Cost. Helium is a finite resource and prices vary widely by country.
• Warmth. Helium conducts heat well, and helium-rich mixes can feel colder to breathe. Many divers don't use it as drysuit inflation gas.
• Decompression. Helium moves in and out of tissues faster than nitrogen, which changes decompression schedules and how divers plan gas switches.
• Density. Helium is very light, and adding it is the main tool for keeping gas density down at depth.

How much helium to use, and at what depth to start, is still debated. Our safety articles on narcosis and gas density look at the different approaches.