When the dense cord linking Chris Lemons to the ship above him broke, there was a sickening crack. A critical umbilical cord to the above world carried power, communications, heat, and air to its 100 m (328 ft) diving suit below the sea surface.

While his coworkers recall this lifeline breaking’s terrible noise, Lemons heard nothing himself. He was stuck for a second against the concrete underwater frame on which they had been working, and then he tumbled down towards the ocean floor. His connection to the above ship has vanished, along with any hope of finding a way back.

Perhaps crucially, his air supply had also expired, leaving him with a limited air supply of six to seven minutes. Lemons would witness something that few men have survived to think about over the next 30 minutes at the bottom of the North Sea: he was out of the sea.

I’m not sure that I had a full grip on what was going on, “Lemons says.” I hit my back on the sea bed and was engulfed by a fog all-encompassing. I figured I had a minimal amount of gas on my back, and there were absolutely no chances of getting out of it. A sort of reluctance has come to me. In some cases, I remember being taken over by sadness.

Lemons had been part of a saturation dive team at the Huntington Oil Field, about 127miles (204 km) east of Aberdeen on Scotland’s east coast, replacing piping on an oil well multiplier. To do this job, divers will spend a month working, sleeping, and eating onboard the dive ship in specially built rooms, isolated by a sheet of metal and glass from the rest of the crew. The three divers acclimate to the pressures that they will feel while submerged in these 6m-long tubes.

 

 

It’s an excellent way of isolation. The three divers will speak to their crewmates outside the chamber and see them, but they are cut off from them otherwise. Each team’s members are entirely dependent on each other – it takes six days of decompression before they can leave this hyperbaric chamber or help get inside.

“It’s a peculiar situation,” says Lemons, 39 years old. “You live on a ship surrounded by many men who are just a sheath of metal apart, but you’re isolated from them.

“In some respects, it’s easier to get back from the Moon than it’s from the depths of the sea.” (Read some of the strangest facts about the Apollo Moon missions.)

Decompression is essential as air divers ‘ nitrogen gas breathes when dissolving underwater into their lungs and tissues at depth. When they come to the surface, the surrounding water pressure is raised, and the bubbles out of the nitrogen. If this occurs so fast, it can cause painful tissue and nerve damage and even kill if the bubbles develop in the brain – a condition commonly referred to as “the bends.”

Nonetheless, the divers who do this job take risks with their move. He was most sorry with Lemons to spend so long away from his fiancée Morag Martin and the house they shared on Scotland’s west coast.

To Lemons and the two friends with whom he was swimming, Dave Yuasa and Duncan Allcock, the day of 18 September 2012, had begun regularly enough. The three climbed into the diving bell that would be lowered from the container, the Bibby Topaz, to the sea bed where their repair work would be carried out.

 

 

“It’s been an average day at the office in many ways,” Lemons says. Although not as experienced as the other two men, for eight years he had been a diver and for a year and a half had been saturation diving, taking part in nine deep-water dives. “On the surface, the sea was a bit rough, but underwater was pretty clear.”

But, the rough sea would cause a chain of events that nearly claimed the life of Lemons. Diving vessels typically use computer-controlled navigation and propulsion systems, known as dynamic positioning, to keep them above the dive site while people are in the water.

The dynamic positioning system of the Bibby Topaz suddenly failed as Lemons and Yuasa started repairing the piping underwater with Allcock supervising them from the bell.

Alarms sounded on the seafloor in the communications system of the divers. Lemons and Yuasa were ordered to return to the whistle. But as they started to follow their umbilical cords, the ship had already drifted back over the excellent metal platform on which they had been working, so they had to crawl over it.

But, as they reached the rim, the umbilical of Lemons got snagged on a piece of metal that stuck out of the frame. The spinning ship held it firmly before he could free it, pulling it into the metal beams.

“Dave noticed that something was wrong and turned back to me,” says Lemons, whose experience turned into a feature-length Last Breath documentary. “We had this strange moment in which we looked into the eyes of each other. He was flailing desperately to get me, but he was pulled away by the boat. I didn’t have any gas before I knew it, because the cable was so tight.”