Diving with Hydrogen – It’s a Gas

When most people think of hydrogen, they think of the fuel that stars burn in their nuclear fires, the hydrogen bomb, or the Hindenburg disaster. Hydrogen is known for its combustibility and explosiveness. Not many people would think of diving underwater with it.

Technical divers breathe various gas blends, using mixtures of nitrogen, oxygen and even helium. But leave it to the ever inventive Swedes, makers of some of the best diving equipment in the world, to use hydrogen as an experimental diving gas as early as the 1940s.

Hydrogen will not burn under two conditions; if there is too little hydrogen, or too much hydrogen and not enough oxygen. A gas mixture (air or oxygen) with less than 4% hydrogen will not burn, and with more than 94% hydrogen in oxygen (or 75% hydrogen in air), the gas mixture will also not burn. So 100% hydrogen will not burn, unless it leaks out of its container and gets diluted in air. And then if there is an ignition source, woosh, a la Hindenburg.

 

A diver with supposed nitrogen narcosis. Photo credit, Daniel Kwok on flickr.

So why would anyone consider breathing hydrogen? When diving deeper than a few meters, you need a so-called diluent gas to mix with oxygen. Air is a mixture of nitrogen and oxygen, and when compressed, that nitrogen becomes narcotic, leading to nitrogen narcosis, or “rapture of the deep”. When air is compressed it also becomes dense, making it more difficult to breathe than air is at the surface.

Helium, often used by deep diving Navy and technical divers, is less dense than nitrogen and therefore is easier to breathe at depth. Furthermore, it is not narcotic, so no more “rapture of the deep”.

But for seriously deep diving, greater than about 450 msw (~1500 fsw), even a mixture of helium and oxygen becomes dense enough to impede breathing. One solution is to use an even lighter gas, hydrogen.

Experimental hydrogen-helium-oxygen gas mixtures have been used by COMEX in France to slightly exceed, at 2290 fsw (701 msw), the U.S. deep diving record (2250 fsw, 686 msw) set using a mixture of helium, nitrogen and oxygen.

Hydrogen has one annoying property — it is narcotic. It is far less narcotic than hyperbaric nitrogen, and some narcosis seems to be necessary to counteract the deleterious effects of the High Pressure Nervous Syndrome (HPNS). However, unlike nitrogen narcosis, which is akin to mild alcohol intoxication, hydrogen narcosis is reported to be psychotropic, inducing at great depth altered realities akin to those produced by LSD.

I once was conducting medical research on a 450 msw dive at the German GUSI deep diving chamber, and one of the divers was a French diver who had been a subject on the French hydrogen dives. He reported, without going into detail, that he did not like the effects of hydrogen at all. It was strange, he said. On the other hand, the same diver did very well on the helium-nitrogen-oxygen gas mixture used at GUSI and Duke University.

That some exotic gases on deep experimental dives would be considered strange is an understatement. Deep hydrogen has been reported to produce out of body experiences, something that a person as well grounded as a professional diver would consider frighteningly bizarre.

Swedish diver Arne Zetterström

The Swedes, and Arne Zetterström in particular, were interested in hydrogen diving during World War II for a simple reason; they wanted to dive deep, without the effects of nitrogen narcosis, but did not have access to helium. Most helium comes from gas wells in the United States and Russia. So, looking for another diluent gas other than helium, Zetterström briefly considered two constituents of intestinal gas (flatus), namely methane and hydrogen. Arguably, it was easy for the Swedes to produce plenty of methane and hydrogen. Just how they planned to do that is something I never asked.

Eventually, hydrogen was chosen for the Swedish dives simply because hydrogen was less dense than methane.

In principle, hydrogen could be used by a deep technical diver, but only at depths deeper than 132 fsw (5 atmospheres), a depth which would turn the noncombustible 4% oxygen in hydrogen gas mix into a so-called normoxic gas mixture, meaning it would have about as many oxygen molecules per breath as air at the surface. If the diver attempted to come shallower on that same gas mixture, he would lose consciousness due to hypoxia.

Since helium is not a combustible gas it does not have gas mixture restrictions. As long as  a helium-oxygen gas mixture contains the right amount of oxygen (not too much and not too little), then it will be safe. Both nitrogen and helium are therefore far preferred over either of the flammable gases methane and hydrogen  for use in breathing gas mixtures for diving.

Nevertheless, as divers continue to explore ways of diving deeper, it is certainly possible that hydrogen and other exotic gases may eventually play a role in deep life-support. Who knows, perhaps a perfect gas mixture will involve a blend of hydrogen and methane along with oxygen. If so, perhaps we could call it, oh I don’t know, maybe … Flatogen!

 

 

 

 

 

Why Deep Saturation Diving Is Like Going to the Moon, and Beyond

This week, as the Space Shuttle is making its last circuits around our planet, I lament what has happened to our space program. Yet, I am reminded of another exploration program that has, like the shuttle and the moon programs, reached incredible milestones only to retreat to a less exotic but still impressive status. That other program is experimental, deep saturation diving.

I have been privileged to conduct human physiological research on several deep saturation dives, one being a record-breaking U.S. Navy dive at the Navy Experimental Diving Unit (NEDU) in 1977 to a pressure equivalent to that found at 1500 feet sea water (fsw), or 460 msw*, and on a 450 msw (1470 fsw) dive at the GUSI diving facility at the GKSS Institute in Geesthacht, Germany in 1990. For perspective, the safe SCUBA diving depth is considered to be 130 fsw, although technical and cave divers often descend deeper, to 300 fsw or so.

NEDU, Panama City, FL

Dives in hyperbaric chambers like at GUSI and NEDU are simulated; the divers don’t actually go anywhere. But the effects of the high pressure on the divers’ bodies are just as they would be in the ocean. Of course, even in simulated dives, divers wear Underwater Breathing Apparatus, and descend into water contained within the hyperbaric complex.

In 1979, NEDU again set the U.S. Navy record for deep diving to 1800 fsw (551 msw). At Duke University in 1981, the U.S. record for pressure exposure was set by three saturation divers inside an eight-foot diameter sphere. The internal pressure was 2250 fsw (686 msw). One of those divers went on to become the senior medical officer at NEDU, none the worse for his high pressure exposure.

The French company Comex, of Marseille used an experimental gas mixture of hydrogen-helium-oxygen to reach 675 msw, before being forced back to 650 msw due to physical and physiological problems with the divers. However, like teams attempting the summit of Mount Everest, one diver from the dive team was pressed to a world record of 701 msw (2290 fsw), just squeaking past the U.S. record.

There is a poorly understood physiological barrier called the High Pressure Nervous Syndrome (HPNS) that limits our penetration to ever deeper depths. In spite of the use of increasingly exotic gas mixtures, helium-oxygen in the U.S. Navy, helium-nitrogen-oxygen at Duke University, and hydrogen-helium-oxygen at Comex, all attempts to dive deeper have, to date, been rebuffed.

Just as I had thought as a young man that trips to the moon would be common-place by now, I had also assumed diving to 3000 feet would be routine. But it is not.

In my early research days I was interested in the effects on organisms of very high pressure, 5000 psi, which is equivalent to a depth of over 11,000 feet (3430 meters). We now know those effects can be profound, altering the very structure of cell membranes. Reversing those effects while maintaining high pressure, at great depth, is a daunting scientific task. We don’t yet know how to do it.

What we do know is that reaching 1500 feet can be done without too much difficulty. In the 1980s it became almost routine to dive to 1000 feet at both the Naval Medical Research Institute (Bethesda) and NEDU. Deep saturation diving is a thriving business in the oil fields of the Gulf of Mexico and the North Sea.

Click for a larger image.

But as for the similarity between deep saturation diving and NASA’s moon missions, in the Apollo program it took slightly over three days to get to the moon, and almost an equal time to return. But as the above dive profile shows, it took sixteen days to reach the maximum depth of 1500 fsw, and seventeen days to safely return. Over that period of time astronauts would have whizzed past the moon and been well on their way to Mars. Unlike spacecraft and astronauts, divers must slow their descent to avoid HPNS, and must slow their return to the surface to avoid debilitating and painful decompression sickness. Diving without submarines or armored suits is very much a demanding, physical stress.

Politically, exceeding our current depth limits of approximately 2000 feet is akin to returning to the moon, and going beyond. We could do it, but at what cost? Should we? Will it ever be a national priority?

Maybe not for the United States, but I have a suspicion that other countries, perhaps not as heavily committed to space as we, will find the allure of beating current diving records irresistible. If there are medical or pharmacological interventions developed for getting divers safely and productively down to 3000 feet, then that would be a scientific achievement comparable to sending men to Mars.

*[The feet to meters conversion is slightly different from the feet of sea water to meters of sea water conversion. The latter represents pressure, not depth, and therefore includes a correction factor for the density of sea water.]