BBC – Future – Can you survive if you run out of air?

There was a disgusting crack when the big cable connecting Chris Lemons to the ship above him crashed. This essential umbilical cord in the world allowed his diving suit to move 100 meters below the surface of the water.

While his colleagues remember the terrible noise of this line of life, Lemons himself heard nothing. For a moment, he found himself stuck against the underwater metal structure they were working on, and then collapsed back to the bottom of the ocean. His connection with the above ship had disappeared, as had all hope of finding him again.

More importantly, his air supply had also disappeared, leaving him only six or seven minutes of emergency air. Over the next 30 minutes at the bottom of the North Sea, Lemons would experience something that few people have lived to talk about: it ran out of air.

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"I'm not sure I have a good idea of ​​what's going on," recalls Lemons. "I hit the bottom of the sea on my back and I was plunged into total darkness. I knew I had a very small amount of gas in the back and that my chances of getting out were almost nonexistent. A kind of resignation came on me. I remember being overcome by sorrow in some ways.

The lemons were part of a saturated diving team that was repairing the piping on an oil well collector at the Huntington oilfield, about 204 km east of Aberdeen, on the east coast of Scotland. To do this job, divers must live, sleep and eat for a month in specially fitted out aboard the dive ship, separated from the rest of the crew by a sheet of metal and glass. In these 6 m long tubes, the three divers acclimatize to the pressures they will experience once under the water.

This is an unusual form of isolation. The three divers can talk and see their teammates outside the room, but they are otherwise cut off from them. The members of each team are completely dependent on each other – it takes six days of decompression to leave this hyperbaric chamber or for help to get inside.

A kind of resignation came on me, I remember being overcome by grief in some ways – Chris Lemons

"It's a very strange situation," says 39-year-old Lemons. "You live on the boat surrounded by many people who are just a metal sheath, but you are completely isolated from them.

"It is faster to return from the moon than from the depths of the sea in some ways."

Decompression is necessary because the air nitrogen that the divers breathe breathes as the water dissolves into the blood and tissues when they are deep down. Going up to the surface, the pressure of the surrounding water is raised and the nitrogen bubbles. If this happens too quickly, it can cause painful tissue and nerve damage and even death if bubbles form in the brain – a condition known as a "curve".

Divers who perform this work, however, take the risks in stride. For Lemons, he was especially concerned about the time he had spent away from his fiancée Morag Martin and the house they shared on the west coast of Scotland.

The day of 18 September 2012 had started normally for Lemons and his two colleagues with whom he was diving, Dave Youasa and Duncan Allcock. The three are mounted in the diving bell, which would be lowered from the ship, the Bibby Topazat the bottom of the sea where they would do their repair work.

"In many ways, it was only an ordinary day at the office," says Lemons. Although less experienced than the other two men, he had been a diver for eight years and had plunged for a year and a half to saturation by taking part in nine deep-water dives. "The sea was a little rough on the surface, but it was pretty clear under the water."

This rough sea would however trigger a series of events that almost cost Lemons life. Normally, dive vessels use computer-controlled navigation and propulsion systems, called dynamic positioning, to keep them above the dive site as long as they have people in the water.

As Lemons and Youasa started to repair the piping underwater, with Allcock supervising them from the bell, the Bibby Topaz's the dynamic positioning system suddenly failed. The ship quickly began to drift.

At the bottom of the sea, alarms were triggered on the divers' communication system. Lemons and Youasa were instructed to return to the bell. But as they began to follow their umbilical cords, the ship had already drifted on the high metal structure they were working on, which meant they had to climb it.

We had this strange moment when we looked in each other's eyes – Chris Lemons

However, when they reached the top, Lemons's umbilical clung to a piece of metal protruding from the structure. Before he could release it, the drifting ship squeezed it hard, dragging it into the metal beams.

"Dave realized that something was wrong and went back to me," says Lemons, whose story was turned into a documentary feature, Last Breath. "We had this strange moment when we were looking into each other's eyes. He was desperately trying to reach, but the boat was moving away. Before I realized it, I did not have gasoline because the cable was tight so tight. "

The tension on the cable had to be immense. Composed of a tangle of pipes and electrical wires with a rope passing in the middle, it cracked as the drifting boat pulled it closer and closer. The lemons instinctively turned the button on his helmet to start the flow of gas from the emergency tank on his back. But before he could do anything, the cable broke, sending him back to the bottom of the sea.

Miraculously, in the dark night, Lemons managed to straighten up and find his way back to the well structure, going up to the top in the hope of seeing the bell and returning to safety.

Without oxygen, the human body can only survive a few minutes before the biological processes that feed its cells begin to fail

"When I got there, the bell could not be found," said Lemons. "I took a measured decision to calm myself down and keep the little gas that I had left. I had only six to seven minutes of emergency gas on my back. I did not expect to be saved, so I just curled up. "

Without oxygen, the human body can only survive a few minutes before the biological processes that feed its cells begin to fail. The electrical signals that power neurons in the brain diminish and eventually stop completely.

"Oxygen loss is at the heart of survival," says Mike Tipton, head of the extreme environments lab at the University of Portsmouth in the UK. "The human body does not have a lot of oxygen, maybe a few liters. How you use it depends on your metabolic rate. "

An adult at rest usually consumes between one-fifth and one-quarter of a liter of oxygen per minute. This can reach four liters per minute when they are exercising.

"If a person is stressed or panicked, it can also increase their metabolic rate," says Tipton, who studied people who survived for long periods without air under water.

They watched helplessly as Lemon's movements gradually disappeared, his life gradually fading away.

Back aboard the Bibby Topaz, the crew desperately tried to manually return to the desired position to rescue their lost colleague. As they moved away, they launched a remotely operated submarine in the hope of finding it again.

At that moment, they stared helplessly at his cameras as Lemons's movements slowly stopped, his life fading away.

"I remember getting the last pieces of air out of the tank," says Lemons. "It takes more effort to suck the gas. It was a little like the moments before your sleep. It was not unpleasant, but I remember being angry and excusing myself a lot with my fiancee Morag. I was angry at the damage that was going to cause to other people. Then there was nothing left.

It took about 30 minutes before the Bibby Topaz crew could regain control and restart the failed dynamic positioning system. When Youasa reached the lemons at the top of the underwater structure, his body was still.

By pure will, Youasa brought his fallen colleague back to the bell and passed it to Allcock. When they removed his helmet, Lemons was blue and no longer breathing. Instinctively, Allcock gave him two mouth-to-mouth resuscitation breaths.

Miraculously, the lemons regained their consciousness.

Common sense suggests that he should have died after so long at the bottom of the sea

"I felt very stoned and there were some flashing lights, but I do not keep many lucid memories of my awakening," says Lemons. "I remember Dave sitting crumbled on the other side of the bell, looking exhausted and not really sure why. It was only a few days later that I realized the seriousness of the situation. "

Nearly seven years later, Lemons is still perplexed about how he managed to survive so long without oxygen. Common sense suggests that he should have died after so long at the bottom of the sea.

But it seems likely that the cold waters of the North Sea played a role – at about 100 m depth, the water was probably below 3 ° C (37 ° F). Without warm water flowing through the umbilical cord to warm up his suit, his body and brain will quickly cool down.

"Rapid cooling of the brain can increase oxygen-free survival time," Tipton says. "If you reduce the temperature by 10 degrees, the metabolic rate drops by half to one-third. If you lower the brain temperature up to 30 ° C (86 ° F), the survival time can increase from 10 to 20 minutes. If you cool the brain to 20 ° C (68 ° C), you can get an hour. "

The pressurized gas that saturation divers usually breathe may have given Lemons an extra chance. When you breathe a lot of oxygen under pressure, it can dissolve into the bloodstream, thus providing the body with additional reserves.

Go hypoxic

Divers are perhaps the most likely people to experience a sudden loss of air supply. But there are many other situations in which the oxygen supply can be cut off. Firefighters often use breathing equipment when entering smoke-clogged buildings, while high-altitude jet fighter pilots also use breathing masks.

At the extreme low end, a lack of oxygen – called hypoxia – can affect many other people. Mountaineers experience low levels of oxygen when they are in the high mountains, a condition often attributed to accidents. When oxygen levels drop, brain function can suffer, leading to poor decisions and confusion.

Patients undergoing surgery will often experience mild hypoxia, which could have an impact on their recovery. Strokes are also caused by the lack of oxygen in a patient's brain, resulting in cell death and injuries that can have lasting effects on one's life.

"There are many diseases where hypoxia is the final stage," says Tipton. "One of the things that happens is that hypoxic people start to lose their peripheral vision and end up looking at a point. This is thought to be the reason why people claim to have seen a light at the end of the tunnel in near-death experiences. "

Children and women are more likely to survive because they are smaller and their bodies tend to cool much faster – Mike Tipton

Lemons himself survived his time without oxygen unscathed. He found only a few bruises on his legs after his ordeal.

But its survival is not unknown either. Tipton has examined 43 separate cases in the medical literature of people who have been submerged in water for long periods. Four of them recovered, including a two and a half year old girl who survived underwater for at least 66 minutes.

"Children and women are more likely to survive because they are smaller and their bodies tend to cool much faster," says Tipton.

Training saturated divers like lemons can also inadvertently teach their bodies how to cope with extreme situations. Researchers at the Norwegian University of Science and Technology (NTNU) in Trondheim discovered that saturation divers adapted to the extreme environment in which they work by changing the genetic activity of their blood cells.

"We have seen a marked shift in genetic programs for the transport of oxygen," says Ingrid Eftedal, head of the barophysiology research group at NTNU. Oxygen is transported around our body in hemoglobin, a molecule found in our red blood cells. "We found that gene activity at all levels of oxygen transport – from hemoglobin to red blood cell production and that the activity of red blood cells is denied during saturation diving, "adds Eftedal.

She and her colleagues think that this could be an answer to the high concentrations of oxygen that they breathe when they are under water. It is possible that the slowing down of oxygen transport in the lemon body has allowed it to extend its life.

Pre-dive exercises have also been shown to reduce the risk of elbows.

Studies of indigenous peoples who usually dive free without additional air have also shown how the human body can adapt to life without oxygen. In Indonesia, the Bajau can reach 70 meters deep while holding their breath as they search for food with spears.

Melissa Ilardo, an evolving geneticist from the University of Utah, discovered that the Bajau genetically evolved to have spleens that are 50% larger than their terrestrial neighbors, the Saluan.

With larger rats, it is thought that the Bajau benefit from a greater injection of oxygenated blood and may retain their breath longer.

The spleen is thought to play a key role in allowing humans to dive freely.

"There is a phenomenon called diving reflex in mammals, which is triggered in humans by the combination of holding your breath and plunging into the water," says Ilardo. "One of the effects of the dive reflex is the contraction of the spleen. The spleen acts as a reservoir for oxygen-rich red blood cells and, as it contracts, these red blood cells are pushed into the circulation, providing additional oxygen supply. This can be considered as a biological dive tank.

With larger rats, it is thought that Bajau have greater oxygenated blood injection and can hold their breath longer. A Bajau diver met by Ilardo told him that he had spent 13 minutes under water.

The lemons themselves returned to diving about three weeks after his accident – at the very place where it had happened, to complete the work that they had started. He also married Morag and they have a daughter together.

Reflecting on his collapse with death and his miraculous survival, he does not take much credit for his own actions.

"One of the main reasons I survived was the quality of my surroundings," he says. "In truth, I have done very little. It was the professionalism and heroism of the two people in the water with me and everyone aboard the ship. I was very lucky. "

His accident triggered a number of changes in the world of diving. They are now using emergency tanks that carry 40 minutes of air instead of five. The umbilical cords are now covered with light garlands, making them easier to see underwater.

The changes in his own life have not been so dramatic.

"I still have to change diapers," he jokes. But he finds himself thinking about death differently. "I do not see that as something to fear. It's more than what you leave behind. "

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