Meet the divers attempting to determine how deep people can go

200 thirty meters into one of many deepest underwater caves on Earth, Richard “Harry” Harris knew that not far forward of him was a 15-meter drop resulting in a spot no human being had seen earlier than. 

Getting there had taken two helicopters, three weeks of take a look at dives, two tons of kit, and arduous work to beat an sudden variety of technical issues. However within the second, Harris was hypnotized by what was earlier than him: the huge, black, gaping unknown. 

Staring into it, he felt the acquainted pull—possibly he might go just a bit farther. As a substitute, he regarded to his diving companion, Craig Challen, floating just a few toes to his proper. That they had each been diving more and more harmful and unplumbed caves for years, making them two of solely a handful of individuals with the talents to help within the rescue of the Thai soccer group that obtained trapped in a single in 2018. They knew excessive danger, and one another, nicely. Even by way of the goggles and the mouthpiece of the respiration equipment, its 4 thick hoses curling round his face like mammoth tusks, Harris might see that Challen felt the identical manner. They each needed very badly to push ahead into the darkish expanse.

As a substitute, on Harris’s cue, they turned again. They weren’t there to exceed 245 meters—a depth they’d reached three years earlier. Nor had been they there to set a depth document—that will imply going previous 308 meters. They had been there to check what they noticed as a doable key to unlocking depths past even 310 meters: respiration hydrogen.

The issue has existed for greater than a century: How can a human physique face up to underwater strain considerably previous its pure threshold? Naval models and offshore oil corporations world wide have lengthy been invested in figuring it out for energy and revenue, and within the 1970s and ’80s their analysis started filtering into the civilian world, the place folks had been testing the bounds of their very own curiosity.

Dr. Richard "Harry" Harris
In 2023, Richard Harris made an experimental dive to find out
whether or not hydrogen might allow exploration at higher depths.

This included folks like Sheck Exley, a highschool math trainer in Dwell Oak, Florida. Exley grew to become a world icon within the diving group for his record-breaking dives—exceeding, in some circumstances, the bounds of the army and industrial professionals. He had been diving the underwater caves of North Florida since he was a teen—by 1972, at age 23, he was the primary particular person on the planet to log 1,000 cave dives—and exploring them is what pushed him to go deeper. He’d been hooked since his first cave dive in Crystal River, Florida, in 1966. “I type of wandered off into the cavern there, my eyes adjusted, and I swam somewhat bit additional, peering off into the darkness,” he informed AquaCorps, {a magazine} for divers, in 1992. “I assume I’ve been peering off into that darkness ever since.”

At round 40 meters, respiration the fuel combination we name air—78% nitrogen, 21% oxygen, and 1% hint gases—causes inert fuel narcosis, or the “martini impact,” named for the incapacitating state it induces. Slightly deeper and oxygen turns into poisonous. For years, the US and British navies had been utilizing helium to dilute the oxygen and nitrogen in a diver’s tank as a method of counteracting each these issues, however few outsiders knew about it. In 1981, after the German cave diver Jochen Hasenmayer reached 143 meters utilizing a helium combination, Exley began utilizing it as nicely—regardless of the information that just a few years earlier, two divers in Florida had experimented with the combination and died. 

Divers who go previous 40 meters usually don’t use a continuing fuel ratio—they cycle by way of mixes of nitrogen, oxygen, and helium as they descend and ascend, modifying them in line with location, water temperature, neurological tolerance to narcosis, and lots of different variables. Decompression tables, which lay out totally different fuel mixtures and the period of time to be spent respiration them, present a exact street map for this course of—very vital, as ascending too shortly releases the amassed gases in a diver’s blood and tissue the best way unscrewing the cap on a bottle of soda releases bubbles, ensuing within the painful, usually debilitating situation referred to as the bends. With out the tables, ascending from nice depths was too dangerous. However producing them required high-level know-how and archives of information unavailable to most individuals.

Exley was in a position to persuade a good friend who labored in industrial diving to present him a pattern desk, which he used to extrapolate previous 121 meters, working all the things out on his pc. In 1987, guided by this info, he used helium to efficiently break the 200-meter diving barrier at Nacimiento Mante in Mexico—a 24-minute descent that compelled him to remain underwater for 11.5 hours to decompress. Over that interval, he felt himself turning into dangerously weak. His blood sugar dropped, the chilly seeped into his limbs, and his uncovered arms and face started to develop wrinkly, develop into uncooked, after which flake. “On the time I felt I might have dived deeper,” he informed InDepth journal that 12 months. “However I knew that I had reached my decompression limits.” 

In 1988, Exley beat his personal document, hitting 237 meters utilizing a extra exact desk generated by the physiologist Invoice Hamilton. Recognized amongst divers as “The Prince of Gases,” Hamilton had been concerned with among the earliest work on decompression previous 200 meters. 

He had helped develop a pc program that generated extraordinarily exact tables calibrated to any variety of parameters, which he created for industrial diving corporations and navies world wide. “By them, he had staggering quantities of information,” says Invoice Stone, an aerospace engineer and cave diver who constructed and offered an early rebreather—a kind of respiration equipment that recycles exhaled air by scrubbing it of carbon dioxide. “He processed all that and developed stochastic fashions that found out the place you may achieve pace on decompression and never harm your self.” Within the ’80s, Hamilton made the unprecedented transfer of making customized tables for individuals who weren’t industrial or army divers, eternally endearing him to the diving group. 

However in 1994, Exley died making an attempt to achieve the underside of the Zacatón sinkhole in Mexico, 332 meters down—he obtained to 270 meters. A possible issue was high-pressure nervous syndrome (HPNS), a neurological situation involving uncontrollable tremors caused when a diver descends too quickly at excessive strain previous 150 meters. Including nitrogen to the combination of helium and oxygen might assist—nitrogen’s narcotic results might dampen the signs. However at that depth, including extra nitrogen would make it harder to breathe due to the fuel’s density, and the narcosis can be debilitating. 

Divers nonetheless pushed previous Exley’s document into 250 after which 300 meters, white-knuckling by way of the HPNS signs. However at such depths, helium turns into too heavy for the human physique to course of. “As you go deeper, for each 10 meters you get an additional ambiance of strain—so as soon as we’re down at these depths of 250 meters, that’s 26 atmospheres,” Challen, Harris’s dive companion, informed me. “It turns into a bodily downside of transferring the fuel out and in of your lungs.” With a purpose to alleviate this downside, divers would wish to breathe one thing lighter than helium. 

“And we’ve solely obtained one lighter fuel to make use of,” Challen says. “After hydrogen, there’s nothing.”

What grew to become referred to as the H2 Working Group started as a “thought experiment,” in line with Michael Menduno, a veteran cave diver and editor in chief of InDepth journal, who introduced everybody collectively in collaboration with John Clarke, the previous scientific director of the US Navy Experimental Dive Unit. It was additionally a method to socialize the best way scientists, engineers, and tinkerers understand how: by arguing over the best way to make one thing work. 

The thought for the working group emerged in 2020, when Menduno, whereas researching an article on deep dives previous 250 meters, concluded that the diving world had reached its restrict with helium. Exley himself had pointed to what he noticed as the subsequent step in reaching unprecedented depths: “From what I’ve been studying, there appears to be some actual potential for hydreliox”—that’s, an oxygen-helium-hydrogen combine. Nonetheless, “nobody has checked out its use for deep bounce dives,” he informed Menduno in a 1992 interview, referring to dives with out using a chamber to assist the diver attain a secure fuel saturation level earlier than venturing into the water.

When the group shaped in that 12 months, at the start of the pandemic, Menduno was accustomed to earlier makes an attempt to make use of hydrogen. Within the ’90s he had traveled to France to observe a group of medical medical doctors, engineers, scientists, and trial divers from Compagnie Maritime d’Expertises (Comex), a Marseilles-based firm specializing in deep diving techniques and gear, try and cross 701 meters in a hyperbaric chamber pumped with a hydrogen fuel combination. (It required 15 days of compression and 23 days of decompression.) This was Hydra 10, a part of a collection of experiments utilizing hydrogen. After Hydra 12, in 1996, the mission had scrapped pursuing hydrogen altogether. Corporations had been turning to manned underwater autos and saturation diving—that’s, staying at excessive depths lengthy sufficient to permit the inert fuel to completely dissolve in a diver’s blood, which is simply doable with a chamber. “[In commercial diving] there’s no poetry, no humorousness—you simply need to be environment friendly,” says Jean-Pierre Imbert, who labored on the Hydra mission and had invited Menduno to watch the experiments within the ’90s.

At 40 meters, the fuel combination we name air turns into incapacitating. Slightly deeper and oxygen turns into poisonous.

In 2012, constructing on Comex’s work, a group of Swedish divers, known as the Hydrox Challenge, had efficiently breathed a combination of hydrogen and oxygen for 5 minutes at 40 meters. They had been hesitant to share the data, involved that individuals with out the experience may make the try at their peril. “We didn’t publish or inform an excessive amount of about how we did it, as a result of we consider for those who do that improper—it’s important to perceive it, or you’ll fail miserably,” diving engineer Åke Larsson, one of many members of the Hydrox Challenge, later stated. “Nevertheless it’s not rocket science. For those who do your homework, it’s not sophisticated. However it’s important to do it proper.” 

That was the historical past on Menduno and Clarke’s minds after they started calling up consultants within the area to debate whether or not it might be doable for a diver exterior a chamber to descend past 200 meters respiration hydrogen. Every member was an professional in a special aspect of what can be concerned in such a dive—the mechanics of the respiration equipment, the calculation of fuel mixtures, the physiological points to be overcome as divers coped with chilly and strain. By the top of the primary assembly, they’d give you so many potential issues they created what they known as a “problem tree” to prepare them; members gravitated towards their areas of experience and got here again to current doable options to the group. The tree saved branching; options begat new issues. 

Challen helps Harris
gear up in 2020; in entrance are twin Megalodon rebreathers, one containing an oxygen-helium-hydrogen
combine, the opposite the usual oxygen-helium-nitrogen.

Harris joined the working group at Menduno’s invitation. The group of divers he was part of, the Wetmules, had reached 245 meters on the Pearse Resurgence, the supply of the Pearse River in New Zealand, however the cave stretched on, and so they needed to map it. They knew that helium was not going to get them previous 300. Hydrogen, nevertheless, was nerve-racking. “I don’t actually need to be the guinea pig who famously popped below water after switching to hydrogen,” he informed the group on the first assembly. “So it’d be good if we are able to clear up that.”

Hydrogen—because the Hindenburg catastrophe confirmed the world—is very flammable. A spark lots of of instances smaller than the slightest quantity of static you may really feel in your fingertip can be sufficient to ignite it. And even when such a spark didn’t trigger an explosion, it might nonetheless set the fuel on hearth. “For those who’re respiration that blend when it’s burning,” Clarke informed the group, “it’s going to be a really disagreeable dive.”

David Doolette, a analysis physiologist on the US Navy Experimental Diving Unit who had himself dived the Pearse Resurgence within the ’90s, was skeptical however thought-about himself “dihydrogen-curious,” referring to the molecular construction of hydrogen fuel. For one factor, its thermal properties imply divers danger hypothermia. “It’s gonna suck the warmth out of your physique to a harmful degree,” he informed the group. And there was no knowledge obtainable to calculate the suitable decompression instances. “It’s going to be a problem to do the decompression calculations,” he informed the group. “Properly, not a problem doing that—that’d be simple. It’d be a problem to get them proper in order that they had been secure to dive.” 

Harris at the mouth of a cave in diving gear with 3 men to the right looking on.
Harris begins the primary
reported hydrogen rebreather dive, at New Zealand’s Pearse
Resurgence in 2023.

Others shared his skepticism. Nuno Gomes, a former world-record-holding cave diver, was notably involved about decompression. “I believe if we’re going to go along with this, we’re going to should progress slowly,” he informed the group. “Begin with shallow dives and progress to deeper and deeper dives.” However in line with Doolette and Stone, the aerospace engineer, it quickly grew to become clear that Harris had already determined to attempt hydrogen within the Pearse Resurgence. At a convention in Australia in 2022, as members of the H2 Working Group met as much as speak in particular person, Imbert stated that going past 3.5% hydrogen would possible set off a detonation. 

“Harry nods and goes, ‘Properly, I don’t suppose that’s true,’” Stone informed me. Imbert requested how he might show that. “Harry says, ‘Properly, final week I did 7% in my pool.’ Everyone perked up.” 

Harris had ordered a canister of hydrogen delivered to his suburban house in Adelaide and, as he later defined, “determined to have a little bit of a play with it.” He rigged his rebreather for hydrogen and put it in his yard pool, hoping to include any potential blast. He crammed the rebreather with hydrogen after which, backing manner from the pool, started to introduce oxygen. (His canine noticed from exterior the pool fence; his spouse was out.) 

When nothing exploded, he began adjusting the ratio of oxygen and hydrogen, turning into assured sufficient to attempt utilizing the rebreather himself. His first sip, he later informed me, felt gentle, slippery, and chilly. It was virtually delightfully simple to breathe. “Hydrogen voice is way sillier than helium voice,” he informed me. “And I used to be happy the home and the canine had been intact.”

The others had been amazed. Some had been perturbed. “Everyone has to make this determination for themself,” Stone informed me. “The Pearse Resurgence will not be a spot to experiment. If you go in there, you ought to be utilizing gear and strategies that you already know are going to work at that depth. You don’t need to be doing physiological experiments at 300 meters’ depth. That’s what killed the entire different divers who went past 200 meters’ depth. So my recommendation to Harry and anyone else who desires to play this sport is similar as what I gave Exley: Go. To. A chamber. Simulate this primary.”

“The group was kind of break up,” Menduno informed me. “I imply, everyone was supportive of Harry, however there have been some folks within the group that thought: You’re gonna die. Among the folks within the group had been upset and fearful that their good friend was going to go off and do that factor and probably die.”

Across the first nook of the Pearse Resurgence, the sunshine disappears, as if the darkish partitions, black marble striated with veins of grey quartz, have absorbed it. The cave typically narrows a lot that for those who stood, you may contact the ceiling. Different components billow out into huge chambers. At one level, jagged fingers of rock bristle from the partitions. Different, deeper components of the cave are easy and virtually completely spherical, damaged solely by darkish fissures that result in unexplored tunnels. 

As every part of the cave will get found, it receives a reputation. Happening in February 2023, Harris and Challen handed by way of the Nightmare Crescent, the Needlebender, the Gargleblaster, Weaver’s Ledge, the Huge Room, and eventually the Brooklyn Exit. The water was 6 °C and completely clear. Except for the transient hisses and clicks of the rebreathers—the crackle of the solenoid triggering, the sigh of gases being pumped by way of the loop—there was an otherworldly silence.

At 120 meters, the cave opens up onto a plateau that drops off into an abyss. “At that time it’s like standing on the precipice,” Harris informed me. “And it appears like you might be actually starting the journey.” 

The abyss takes you down 50 meters by way of a vertical tunnel. By 170 meters, Harris might monitor the place he was on the map in his head, following acquainted rock formations. They needed to protect their power and stop carbon dioxide buildup of their joints, in order that they restricted their motion, counting on underwater scooters to maneuver. They slowly tied off at totally different factors within the descent, working round ropes left behind from dives previous, a few of which had been put in by Doolette 20 years earlier than. 

At 230 meters, Harris had executed one thing no person had executed earlier than—swimming freely to unimaginable depths and inhaling hydrogen.

Harris remembers that though his thoughts was absorbed with their strict plan, hypervigilant to any unusual noises from his rebreather that would imply failure, he took a second to pause, considering: “What if I by no means obtained to see this once more?” 

At 200 meters, Harris launched the hydrogen. For the subsequent 30 meters he gauged his physique’s response. He was calm, clearheaded, however much more, he observed that the sunshine tremors in his arms he often obtained at this depth, an early signal of high-pressure nervous syndrome, had disappeared. He regarded to Challen, who was utilizing helium, as he tied off the rope: his dive companion’s arms had a visual tremor. 

At 230 meters, Harris had executed one thing no person had executed earlier than—swimming freely down to those unimaginable depths and inhaling hydrogen—however his eyes had been skilled just a bit farther, to the unexplored drop solely 15 meters away. “I might be mendacity if I didn’t say I dream about taking place there,” he later informed an viewers in Malta. 

These obsessive about studying the best way to put the human physique below unimaginable quantities of strain make up a comparatively small group; for probably the most half, everyone is one diploma of separation from everybody else. Clarke, the Navy scientist, and Susan Kayar, a physiologist and professional in decompression who was additionally a part of the H2 Working Group, had each labored on the Navy Medical Analysis Institute within the ’90s. That they had misplaced contact, however they reconnected after each printed novels that included a scene with a hydrogen dive—hers for a rescue mission, his to get well a UFO that had crashed into the ocean. “Hers is extra life like in that regard,” Clarke says. “I hadn’t spoken to Susan in 30 years, after which we lastly came upon: Gee, we’re considering very a lot alike!”

Challen below the seven-meter habitat erected a brief distance into Nightmare Crescent within the Pearse Resurgence. The habitat has seats so divers can sit in a dry setting through the last decompression cease.

Doolette, the analysis physiologist skeptical about utilizing hydrogen, has recognized Harris for greater than 20 years, ever since Harris took Doolette’s diving drugs qualification course in Australia. On the time, they had been additionally each working within the hyperbaric medical unit on the Royal Adelaide Hospital. Harris needed to get extra superior at cave diving and Doolette was a longtime technical cave diver.

Even earlier than the H2 Working Group started assembly, Doolette knew that Harris was fascinated about diving with hydrogen. “I knew issues had been being deliberate,” Doolette informed me. “It in all probability got here as a shock to among the workshop, however to not me … I knew it wasn’t theoretical.”

However Doolette felt that testing hydrogen on a deep cave dive was too dangerous. “There’s an entire hydrogen business—and their strategy is to exclude hydrogen and oxygen from getting close to one another. So once you’ve obtained to combine them collectively—nicely, there aren’t even procedures, actually,” he says. “I definitely thought it was foolhardy.” 

Stone, too, was skeptical of the expedition—for any dive past 200 meters, he stated, the idea ought to be examined first. “I’ve been doing this for a very long time, and I’ve obtained a whole lot of lifeless mates,” he says. 

“We’re transferring into the zone the place robotics isn’t science fiction,” he continues. “It’s {hardware}, it’s software program—we’re doing it. Is it excellent? No. Nevertheless it’s a pair years away. We’re near doing dives longer than the longest human dives, and with a kilometer-depth ranking it’ll be far, far past even hydrogen diving.”

As a diver, Doolette says, he understands desirous to go the place no person else had been earlier than: “Cave divers and different folks probe for the enjoyment of it. A robotic’s not gonna get that.” The opposite draw, he says, is the puzzle of determining the place the cave goes and the best way to comply with it. And once you lastly get into the water, the remainder of the world falls away. 

A couple of weeks after the hydrogen dive, Harris gave a presentation to the H2 Working Group, apologizing for “sneaking round somewhat bit.” He concluded with a caveat: n = 1. “That means it has been profitable one time,” he stated. When the PowerPoint ended, the group applauded. “Simply one thing you may add to your last slide, Harry,” Doolette stated. “The likelihood of survival is larger than zero.” 

Doolette was relieved when he realized that Harris had made it again to the floor. “I acknowledged that it was a reasonably groundbreaking, momentous dive,” he informed me. “I don’t see the aim of going deep for the sake of going deep, however for those who’re dedicated to an exploration mission and it entails cave diving in pursuit of exploration and discovery, then that’s what you do.”

“There’s all the time somewhat temptation to go that little bit additional. That’s why we’re doing these items,” Challen informed me. “Now we have this faulty facet to our characters that urges us to push on just a bit bit extra.” 

Samantha Schuyler is a author, editor, and fact-checker dwelling in New York.  

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