This deepsea diver was cut off from his air supply for half an hour. 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.

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.