This deep-sea diver was cut off from his air supply for half an hour. He survived

The Current19:46Stranded, this diver lost oxygen for 25 minutes. He survived

Chris Lemons says the day of the accident that would nearly claim his life started like any other.

"It was very much a normal day at the office," Lemons told The Current's Matt Galloway. 

For him, "the office" was the ocean floor, where he spent six hours each day working as a saturation diver servicing offshore oil rigs. Saturation divers live for days to weeks at a time in pressurized chambers in order to stay at the same, very extreme pressure that exists at the bottom of the ocean.

This particular job found him in the middle of the North Sea, working on a large structure called an oil manifold to remove a section of pipeline some 100 metres below the surface. 

Lemons was inside the manifold when alarms started blaring over his communication line to the main ship. The supervisor in command of the three-person dive team told Lemons and his colleagues to get back immediately to the diving bell — a piece of equipment attached to the ship that transports the crew between the boat and the ocean floor.

"You could just tell from the tone of his voice that this was something fairly … serious," Lemons said. "I don't remember really calculating what was going on, but you could tell something was afoot."

Topside, a malfunction in the ship's computer system had caused the captains to lose control of the vessel. Massive waves and winds blew the vessel off course, effectively dragging the dive bell and the divers, who are attached to the bell by a 45-metre "umbilical cord" that supplies them life-giving heat and breathable air.

In the chaotic moments that came next, Lemons' umbilical cord snapped, leaving him stranded without air. He eventually lost consciousness and was without oxygen for about half an hour — yet by a confluence of lucky breaks, good training and science, he walked away unscathed.

The dramatic tale has since been turned into a documentary and, most recently, a feature film called Last Breath, starring Woody Harrelson, Simu Liu, Finn Cole and Cliff Curtis.

Running out of air on the ocean floor

Lemons was working underwater with his colleague, David Yuasa, at the time the alarms sounded. Both men were able to swim out of the manifold, but Lemons quickly realized his cord had snagged on a section of the manifold and he was unable to get free.

The stuck diver felt the tension on his cable grow and grow as the ship continued to drift in the rough swell above him.

"All of a sudden ... I'd become an anchor, basically, to an 8,000 tonne vessel," Lemons said. "And obviously there's only going to be one winner in that situation."

Yuasa saw Lemons struggling and tried to swim back toward him. But Yuasa reached the end of his cable just short of Lemons. The two divers shared one final look before the still out-of-control boat yanked Yuasa away from his colleague and into the darkness of the deep sea water.

Alone, Lemons says his ever-stretching umbilical cord started giving out. He opened the valve to a spare air tank carried on his back. The reserve would help Lemons breathe for an additional eight or nine minutes, he says, though he knew he'd be in trouble after that.

Lemons' umbilical cord finally snapped under the pressure like "a shotgun going off," he recalls. The force sent him tumbling off the top of the manifold, a few metres down to the very bottom of the ocean floor.

He says he knew his life was "on a clock" at that point.

Consumed by panic, the lone diver climbed back up on top of the oil structure in the pitch dark and scoured the surface for the boat. It was nowhere to be seen.

In that seminal moment, Lemons says he realized nobody was around to save him — and saving himself wasn't an option.

"That had a strangely calming effect, I think, knowing that I couldn't do much to help myself," Lemons said. "I resigned myself quite quickly to the fact that this was probably going to be ... the place that I die."

Lemons lay down in the fetal position on top of the structure, where he knew he had the best odds of being found by Yuasa should they circle back for him.

In what he thought would be his final moments, he reflected on his short 32 years of life and all of the things he'd never do — like travel, own a house, or have children. He imagined his parents being informed of his death, and how strange it would be to die in such an alien environment.

"I grew up in a sort of middle class family in Cambridge, you know; how've I ended up dying in this dark, lonely place?" Lemons remembers thinking.

His breathing became difficult and shortly after, Lemons lost consciousness.

By the time the crew was able to regain control of the vessel, circle back to the dive site, send a driverless submarine with a camera called a ROV down to locate Lemons and then have Yuasa perform the rescue, the diver had been severed from his umbilical for about half an hour. That's more than enough time to cause lasting brain damage, if not death — both of which can happen in a matter of minutes.

Lemons isn't much of a believer in luck or miracles, he says, but this case might fit the bill.

"I use the word [luck] quite casually, I think, but yeah, it's hard to deny that," Lemons said. "I certainly feel lucky."

Science and precision, not luck

Jochen Schipke, a now-retired professor of physiology in Germany who co-authored a case report on how Lemons survived the ordeal, doesn't use the word luck. He says it was a matter of "perfection."

Lemons would have used more of his available air right after his cable was severed, when he was feeling panicked and had to climb back on top of the manifold, according to Schipke. But once Lemons resigned himself to dying, Schipke says his breathing would have been very calm, allowing the trapped diver to extend his supply.

The divers were also breathing a mixture of helium and oxygen called heliox, which allows them to maintain proper pressure on the ocean floor. Schipke says helium cools the body, and its use is why Lemons' body temperature had dropped to about 27 degrees Celsius by the time he was back in the bell. 

The body uses less oxygen at colder temperatures, according to Schipke, so this factor would have helped stretch Lemons' limited reserves even further.

The crew's training was important, too, according to the researcher. Lemons was in fantastic physical shape and had 10 years of experience under his belt, while Yuasa, the ROV operator and other crew members all acted quickly and with precision to rescue Lemons.

"This was close to perfection. Not so much luck," Schipke said. "This was training. This was knowledge. This was experience."

Be it by luck, science, perfection or any other factor, Lemons says he is simply glad to be alive.

No great epiphanies or life changes came from the incident, he says — aside from maybe a "more acute awareness" of death. 

"I've found that life takes over, really," Lemons said. "Things are quickly forgotten and you move on and the … banalities of existence suddenly take over."

Within three weeks of the accident, he was back to work as a diver — a job he went on to do for 10 more years. These days, Lemons gives talks about his story at conferences. He also still works in the industry, but as a dive supervisor instead.

"I stay in the dry and the safe," Lemons said. "And I'm quite relieved to say so."