by Reilly Fogarty
Header photo courtesy of DAN.
The pool of people who explore the ocean depths beyond 122 m/400 ft is small, and the group of people who do it regularly and need to reach those depths quickly is microscopic. This niche application coupled with a significant fire hazard make it easy to understand why exotic gases like hydrogen have escaped both common use and public interest.
Despite the obvious concerns, however, hydrogen has shown some capacity to ameliorate the effects of high pressure nervous syndrome (HPNS) in deep divers, improve function at extreme depth, reduce work of breathing, and present a possible alternative to helium in case of helium reserve depletion. Use of the gas has made it possible to dive deeper, get to depth faster, and stay there longer, but there is a substantial risk-versus-reward calculation to be made before considering its use. Interested in diving deep and dabbling in the cutting edge of diving research? Here’s what we know about using hydrogen as a diving gas.
High Pressure Nervous Syndrome
Records of sojourns into the use of hydrogen as a breathing gas go back to as early as the 18th century with the experiments of Antione Lavoisier, but the use of the gas came to a head during the heyday of deep diving research in the late 20th century. From the Atlantis dives at Duke University to the Hydra Missions and the evolution of the Compagnie Maritime d’Expertises (COMEX) tables, researchers and deep divers quickly found issues as they pushed to explore deeper depths. Racing past 184 m/600 ft, researchers discovered that divers would face several new and potentially deadly phenomena in their push to the bottom. Chief among these was a condition that came to be called high pressure nervous syndrome. The condition was first described as “helium tremors” by Russian researcher G. L. Zal’tsman in 1961 and Peter B. Bennett in 1965 (Zal’tsman’s research was not available outside of the Soviet Union until 1967).
Later this condition would be named and correlated with symptoms including tremors, headache, dizziness, fatigue, myoclonic jerking, muscular weakness, and euphoria. Gastrointestinal complaints, memory and cognitive deficits, psychomotor impairment, nightmares, and somnolence are also possible, and convulsions have been noted in animal models (Kangal, 2019). The mechanism of HPNS has not yet been proven, but there are several working theories.
The first of these involves the compression of lipid components of the cell membranes in the central nervous system (CNS). Some theorize that the compression of these tissues may affect the transmembrane proteins, ion channels, and surface receptors critical to the signaling pathways of the CNS (Talpalar, 2007). Many connect the use of hydrogen to mitigate the effects of HPNS to this model. Some research has shown that anesthetic gases can reduce the effects of HPNS, and this has been proposed to be driven by some pressure reversal effect of narcosis (Kot, 2012). Hydrogen is a narcotic gas, and this may be one component of its ability to reduce the onset or severity of HPNS. This mechanism, the compression of lipid components also appears to be the one that initially gave rise to the use of breathing gases as a way to ameliorate the effects of HPNS, with some groundwork for this foundation laid out by Peter B. Bennett, PhD, as early as 1989 (Bennett, 1989).
Other researchers have focused on neurotransmitters, including gamma-aminobutyric acid (GABA), dopamine, serotonin, acetylcholine, and others. These models have also shown promise, one study showing a GABA increase in the cortex diminishing HPNS signs in baboon models and another showing NMDA antagonists preventing convulsions in rats (Pearce, 1989, 1991). Similar studies have been conducted with a range of neurotransmitters and neuronal calcium ion channels with similar results. In short, there are several potential avenues for the specific mechanism of HPNS, and while the general mechanism is likely a combination of several models, none have yet been definitively proven.
What we know is that there is notable variation in HPNS onset among divers (Bennett, 1989), and onset appears to be the result of a combination of breathing gas, compression rate, and depth. Faster compression, lower nitrogen, or hydrogen content in helium/oxygen breathing gases, and deeper depths have been correlated with more rapid onset and more severe symptoms (Jain, 1994).
The Benefits of Hydrogen
The use of hydrogen as a diving gas doesn’t just stem from its ability to reduce the onset of HPNS—it’s an extraordinarily light gas that’s useful in reducing work of breathing at extreme depth and a potential replacement for helium when worldwide demand has led to a quickly dwindling reserve. One U.S. Navy paper went so far as to propose hydrogen replacement of helium due to helium scarcity leading to a predicted depletion of supply by the year 2000 (Dougherty, 1965). Thankfully, that mark has come and gone due to the discovery of several new helium sources, but it’s not an unrealistic concern when the demand for helium is so high in manufacturing, aerospace, and technology.
The benefits of hydrogen are notable, but the hazards are nothing to balk at. Little research has been done on the decompression or thermal properties of hydrogen in divers, it’s reported to be mildly narcotic, and it’s highly flammable. While oxygen is an oxidizer that can feed a fire, hydrogen is actively flammable—in the presence of sufficient oxygen and a source of ignition, it will combust in dramatic fashion. In practice, this combustibility is managed by reducing both the sources of ignition and the available oxygen. With the lower explosive limit of hydrogen being around 4% by volume, using less than this amount in normoxic environments effectively mitigates the fire risk but does little for deep divers. Instead, extremely hypoxic gases and high concentrations of hydrogen and helium have been used with great success. The COMEX Hydra VIII mission, for example, used a mixture of 49% hydrogen, 50.2% helium, and 0.8% oxygen to take divers to a maximum depth of 536 m/1,752 ft.
The decompression profiles used in these deep saturation dives appear to be effective as well. As early as 1992, COMEX researchers found that teams of divers on a hydrogen mixture at a depth of 210 m/686 ft performed tasks more efficiently, both cognitively and physically, than their counterparts on helium (Offshore-mag.com, 1996). The same experiment resulted in a bubble study that showed “no evidence of bubbles” in the divers following decompression—an exercise in small sample sizes perhaps, but with promising results. (Note: Researchers suspected that “biochemical decompression” might be involved, i.e., a process in which metabolism of H2 by intestinal microbes facilitates decompression—ed.) U.S. Navy research found similar results, indicating that hydrogen increased the capacity for physical effort as a result of a decrease in work of breathing at depth (Dougherty, 1965).
Functionally, the benefits of the gas are hard to dispute; work of breathing is a constantly growing area of concern for dives at all depths, HPNS is a constant concern, and minimizing decompression is a perpetual goal. For divers reaching extreme depths without the ability to perform saturation dives, diving to depths beyond 122m/400 ft is a repetitive gamble with no guarantee of success. Rapid compression combined with limited options for gas mixes result in the need to play a dive profile by “feel” with emergency plans in place to respond to HPNS onset, and more than one diver, likely including Sheck Exley (See: “Examining Early Technical Diving Deaths,” by Michael Menduno, InDepth 2.2) has lost their life to the condition.
The Hazards of Hydrogen
By the same token, hydrogen presents unique hazards that require careful consideration. Unexplored decompression profiles and limited research on long-term effects make the decision to dive with hydrogen difficult, and the significant risk of fire places divers in more danger than is typically acceptable. Add to this the limited applications (either hydrogen content below 4% in normoxic environments or oxygen content below 6% in high-hydrogen environments), and it quickly becomes apparent why hydrogen hasn’t yet hit the mainstream.
The presence of project divers in our community performing near saturation dives with trimix and makeshift in-water habitats skews favor away from hydrogen as well, making it a gas viable only for the deepest dives without the option for saturation. The case for hydrogen isn’t entirely up in smoke, however. Research showing significant decompression benefits or depletion of helium reserves may well push us toward helium’s more flammable cousin, but it’s unlikely you’ll see hydrogen at your favorite fill station any time soon.
- Ozgok Kangal, M.K., & Murphy-Lavoie, H.M., (2019, November 14). Diving, High Pressure Nervous Syndrome. (. In: StatPearls StatPearls Publishing.
- Talpalar, A.E., (2007, Nov 16-30). High pressure neurological syndrome. Rev Neurol., 45(10), 631-6.
- Kot, J., (2012). Extremely deep recreational dives: the risk for carbon dioxide (CO2) retention and high pressure neurological syndrome (HPNS). Int Marit Health, 63(1), 49-55.
- Bennett, P.B., (1989). Physiological limitations to underwater exploration and work. Comp Biochem Physiol A Comp Physiol., 93(1), 295-300.
- Pearce, P.C., Clarke, D., Doré, C.J., Halsey, M.J., Luff, N.P., & Maclean, C.J., (1989. March). Sodium valproate interactions with the HPNS: EEG and behavioral observations. Undersea Biomed Res. 16(2), 99-113.
- Pearce, P.C., Halsey, M.J., MacLean, C.J., Ward, E.M., Webster, M.T., Luff, N.P., Pearson, J., Charlett, A., & Meldrum, B.S., (1991, July). The effects of the competitive NMDA receptor antagonist CPP on the high pressure neurological syndrome in a primate model. Neuropharmacology,30(7), 787-96.
- Jain, K.K. (1994, July). High-pressure neurological syndrome (HPNS). Acta Neurol. Scand.,90(1), 45-50.
- Dougherty, J., (1965). The Use of Hydrogen As An Inert Gas During Diving: Pulmonary Function During Hydrogen-Oxygen Breathing At Pressures Equivalent to 200 Feet of Sea Water.
- Saturation diving tests support claims for hydrogen breathing mix, (1996). Offshore-mag.com.
InDEPTH: Hydrogen, At Last? (2023) by Michael Menduno
InDEPTH: N=1: The Inside Story of the First-Ever Hydrogen CCR Dive (2023) by Ashley Stewart
InDEPTH: The Case for Biochemical Decompression by Susan R. Kayar
John Clarke, retired scientific director of the U.S. Navy Experimental Diving Unit, is knowledgeable about hydrogen diving and has used that knowledge both in his blogs as well as in the undersea sci-fi thrillers, the Jason Parker Trilogy , of which he is the author.
Fahlman, A., Lin, W.C., Whitman, W.B., & Kayar, S.R., (2002, November). Modulation of decompression sickness risk in pigs with caffeine during H2 biochemical decompression. JApp. Physio. 93(5).
Kayar, S.R., & Fahlman, A. (2001). Decompression sickness risk reduced by native intestinal flora in pigs after H2 dives. Undersea Hyperb Med., 28(2), 89-97.
Fahlman, A., Tikuisis, P., Himm, J.F., Weathersby, P.K., & Kayar, S,R., (2001, December). On the likelihood of decompression sickness during H2 biochemical decompression in pigs. J Appl Physiol., 91(6), 2720-9.
Reilly Fogarty is a team leader for risk mitigation initiatives at Divers Alert Network (DAN). When not working on safety programs for DAN, he can be found running technical charters and teaching rebreather diving in Gloucester, Mass. Reilly is a USCG licensed captain whose professional background includes surgical and wilderness emergency medicine as well as dive shop management.
Hyperbaric Chambers Are Turning Away Divers. Will There Be One Nearby When You Need It?
Unfortunately, it’s hard to make a business case for treating divers versus wound and burn care victims. As a result, many hyperbaric chambers no longer treat divers, leaving fewer facilities available for divers in need and increasing their post-dive time to treatment. InDEPTH editor Ashley Stewart reports on this growing crisis in the US and what can be done!
By Ashley Stewart
Steven Wells was diving on the scuttled wreck of the USS Oriskany off the coast of Florida in 2016 when a problem with his buoyancy compensator caused a rapid ascent to the surface.
Wells’ dive buddies followed the emergency action plan for the Oriskany listed on the Florida Fish and Wildlife Conservation Commission’s website at the time and brought Wells straight to Naval Air Station Pensacola, the nearest facility with a hyperbaric chamber. The facility turned him away because there was no one there to run it.
Wells was taken 30 minutes away to Baptist Hospital, which also has a chamber capable of treating his injuries, but the hospital had years earlier decided only to use it for wound care. Doctors there decided Wells would be taken by ambulance more than an hour away to Mobile, Alabama, the nearest facility that accepts divers.
By the time Wells arrived at the only chamber that would help him, it was too late.
“I got a call from the hospital saying, ‘Your husband is on life support. You need to get here now,’” Rachel Wells said of her late-husband of more than 23 years.
Julio Garcia — the program director of Springhill Medical Center’s wound care and hyperbaric facility where Steven Wells was to be treated — told InDEPTH that while no one can be certain how sooner treatment would have affected the outcome of Wells’ case, it would have given him the best chance for a full recovery.
Each year in the US, there are about 400 serious cases of decompression illness (DCI) — a category including both arterial gas embolism and decompression sickness — in divers, according to one 2020 paper. The Divers Alert Network (DAN) hotline dealt with 587 cases annually over the past five years.
The availability of hyperbaric chambers to treat decompression illness is something many divers take for granted. We try to avoid dive-related injuries through training, but expect treatment to be available when we need it.
The reality — as Steven and Rachel Wells tragically learned — is that only a minority of divers are close to care for diving-related injuries, according to medical professionals in the field. The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.
The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.
“The problem is only getting worse, not better,” Garcia, the Springhill Medical Center program director, said. Garcia has been sounding the alarm about this problem for more than a decade. His hospital takes patients from as far away as Florida cave country and treated 20 DCI cases in 2022. Those patients had an average transportation time of 11.5 hours, according to an InDEPTH analysis of Garcia’s records.
Florida stands out because it’s a popular diving destination, DAN Research Director Frauke Tillmans said, but the situation is not much better across the US. Many of the 1,500 hyperbaric medicine facilities, like Pensacola’s Baptist Hospital, have transitioned to treating wound care only for economic reasons. Emergency hyperbaric services are expensive to train and staff, and come with increased liability.
Time to treatment can be important in DCI cases
Time is of the essence when treating DCI. Divers Alert Network Director of Medical Services Camilo Saraiva told InDEPTH time to treatment is a “pivotal determinant” when it comes to outcomes for DCI patients. “Swift intervention significantly influences the effectiveness of therapeutic recompression,” Saraiva said.
Decompression sickness, for example, results from rapid changes in pressure and can form gas bubbles in body tissues. Initiating recompression therapy minimizes bubble size and number, Saraiva said, enhancing their elimination and reducing the risk of further vascular obstruction and tissue damage.
“The timely provision of hyperbaric oxygen therapy not only aids in bubble resolution but also mitigates the potential for neurological deficits and other severe complications, highlighting the critical role of early treatment in optimizing outcomes for DCI patients,” Saraiva said.
The 2018 paper “In water-recompression” stated delays to recompression in military and experimental diving are typically less than two hours and more than 90% of cases are completely resolved during the first treatment.
Frank K. Butler and Richard E. Moon, hyperbaric medicine experts, wrote in a 2020 letter to the Undersea and Hyperbaric Medicine journal editors suggesting a minority of patients who need life-saving hyperbaric oxygen treatment (HBO2) are close to a major hospital with a 24-hour emergency hyperbaric facility.
“Despite the urgent need for treatment, most hyperbaric chambers will decline to accept emergent patients at present,” Butler and Moon wrote. “Patients may eventually receive HBO2 but after a significant delay and a transfer of several hundred miles. Many never receive indicated HBO2, often resulting in poorer patient outcomes.”
Patients who are delayed treatment, they wrote, face the possibility in some cases of “death, permanent neurological damage, permanent loss of vision, or loss of an extremity, most of which would have been readily preventable had emergent HBO2 been administered.”
Why fewer chambers treat dive injuries
As recently as two decades ago, according to Butler and Moon, the majority of hyperbaric treatment facilities were available 24/7 to treat emergency patients. The percentage of those facilities now treating emergency patients is unclear, but it’s universally agreed the number has fallen significantly.
The reasons for the loss of emergency HBO2 facilities, Butler and Moon suggest, include “a better economic return when chambers focus on wound care patients as opposed to emergencies; the greater legal liability involved with treating high-acuity emergency patients; and the increased training and staffing requirements that would be required to manage critically ill patients — especially diving injuries and iatrogenic gas embolism patients.”
A letter from an administrator at Baptist Hospital — which sent Steve Wells to Springhill Medical Center — viewed by InDEPTH shows the hospital discontinued hyperbaric emergency services in December 2010, citing lack of staffing for specialty trained hyperbaric physicians who can provide 24-hour patient care. Baptist has yet to respond to InDEPTH’s request for comment.
There’s also the issue of pay. Garcia, the Springhill program director, said the current rate of pay for doctors who administer hyperbaric treatments regardless of length is around $150. A typical hyperbaric treatment for other conditions is about two hours. Diving treatments are usually six or seven, he said. “What doctor wants to get paid $150 to be up all night for seven hours, at that point making less than the technician?” Garcia said. “The fix is that healthcare payers need to pay more for the supervision of the treatment for diving injuries. Make it something that’s worth a doctor’s time besides the goodness of their hearts.”
Silence from lawmakers
Medical and diving organizations in 2020 sent a letter to the House and Senate, federal government agencies, governors of Florida and California, and the American Hospital Association expressing concerns about the lack of availability of chambers to treat diving injuries.
“There are approximately three million recreational scuba divers in the US,” the letter stated. “In the unlikely event that they suffer a diving-related injury, they trust that the US medical system will provide state-of-the-art care for their injuries, but the steadily- decreasing number of hyperbaric treatment facilities in the US willing to treat them emergently for decompression sickness or arterial gas embolism often places them at much greater risk than they realize.”
Garcia has on his own contacted lawmakers, reporters, medical systems — even private space companies like SpaceX because his facility is also the only one nearby treating altitude decompression sickness from space and air travel.
Little has changed, Garcia said.
Garcia showed InDEPTH a 2014 letter from a Defense Health Agency director who said, while there are three Undersea and Hyperbaric Medicine Society-accredited clinic hyperbaric medicine facilities and two additional facilities that can treat civilian emergencies, they are not staffed 24/7 and not designed for patients with other medical illnesses. Garcia at the time requested the creation of a federal grant to support the expansion of 24/7 hyperbaric services, but the director said that was outside of the agencies’ purview.
Two years after this exchange, Steven Wells was taken to and turned away from one of these facilities — the NAS Pensacola, listed on the Florida Fish and Wildlife Conservation Commission’s (FWC) emergency action plan at the time.
The Florida Fish and Wildlife Conservation Commission website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia.
The FWC website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia. A report from the University of West Florida estimated the sinking of the Oriskany, scuttled in 2006, generated nearly $4 million for Pensacola and Escambia County in the next year alone.
An FWC spokesperson said the agency provides diver safety reminders and recommended actions on its website “as a courtesy” and is not intended for emergency response. FWC and Visit Florida did not respond to inquiries about how much Florida’s government spends on advertising the artificial reefs and other diving activities, or whether any effort to expand the availability of hyperbaric facilities to treat the divers who show up as a result.
“My question is what is my husband’s life worth compared to your chambers,” Rachel Wells, Steven Wells’ widow said. “Why did he have to die?”
DIVER: A Crisis in Emergency Chamber Availability by Dan Orr (April 2022)
Divenewswire: A Crisis Lurking Below the Surface Emergency Hyperbaric Treatment Availability by Dan Orr (August 2021)
Undersea and Hyperbaric Medicine (2020): Emergency hyperbaric oxygen therapy: A service in need of resuscitation – an open letter by Frank K. Butler, MD, and Richard E. Moon, MD
InDEPTH: A New Look at In-Water Recompression (IWR) (2019) by Reilly Fogarty
Diving and Hyperbaric medicine (2018): In-water Recompression, Doolette DJ and Mitchell SJ
InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at: email@example.com.