There was a disgusting crack when the thick cable connecting Chris Lemony with the ship above him opened. This vital umbilical cord to the world above was carrying power, communications, warmth and air to his diving suit 100 meters below the surface of the sea.
This article is part of the new BBC future column called "Worst Case", which looks at the extremes of human experience and remarkable sustainability that people show in the face of disaster.
It aims to examine the ways people have dealt with when the worst happens and what lessons we can learn from their experience.
As his colleagues remembered the terrible noise of this rupture, Lemon could not hear anything. In a moment, he had collided with the metal underwater construction they had worked on, and then rolled back to the ocean floor. His connection to the ship above was gone, and he hoped to come back to him.
Most importantly, his air supply has also disappeared, leaving him only six or seven minutes of emergency air supply. Over the next 30 minutes at the bottom of the North Sea, the lemons will experience something that few people have lived to talk about: the air has been exhausted.
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"I'm not sure I had a lot of care about what's going on," Lemony remembers. "I hit the sea bottom on my back and I was surrounded by all-round darkness. I knew I had very little gas on my back and my chances of getting out of it almost did not exist. A sort of resignation came to me. I remember that in some way I was overwhelmed by sorrow.
Lemons were part of the saturation team that fixes oil wealth pipeline in the Huntington oil field, about 127 miles (204 kilometers) east of Aberdeen on the east coast of Scotland. To do this, divers have to spend a month of living, sleeping and eating in specially built camps aboard the diving vessel, separated from the rest of the crew with a sheet of metal and glass. In this 6-meter tube the three divers are acclimatized to the pressure they will experience once under the water.
This is an unusual form of isolation. The three divers can talk and see their crew members outside the room but are otherwise cut off by them. The members of each team are completely dependent on each other – it takes six days of decompression before they can leave this hyperbaric camera or help get inside.
A sort of resignation caught up with me, I remember that I was somehow overwhelmed by sorrow – Chris Lemony
"This is a very strange situation," says 39-year-old Lemon. "You live on a ship surrounded by many people who are only a metal sheath, but you are completely isolated from them.
"It's quicker to get back from the moon than from the depths of the sea somehow."
Decompression is necessary because the nitrogen gas from the air dives breathes and the underwater dissolves in the blood and tissues when they are deep. As they rise to the surface, the pressure of the surrounding water rises and the nitrogen bubbles go out. If this happens too quickly, it can cause painful damage to the tissues and nerves and even lead to death if the bubbles are formed in the brain – a condition known as "bends".
However, divers who carry out this work take the risks in a step. For Lemon, he was most concerned to spend so long away from his fiancé Moraig Martin and the home they shared on the west coast of Scotland.
The day on September 18, 2012 normally started enough for the lemons and the two colleagues they dived with – Dave Youssa and Duncan Alcov. The three of them climbed into the diving bell that was going to descend from the ship Bibi Topazto the seabed where they would do their repair work.
"In many ways it was a simple day in the office," says Lemony. Although he was not as experienced as the other two men, he was a diver for eight years and was a saturated diver for a year and a half, taking part in nine deep-sea dives. "The sea was a bit rough on the surface, but it was pretty clear under the water."
This crude sea would, however, trigger a chain of events that almost promised the life of Lemony. Diving ships usually use computer-controlled navigation systems and drive systems – known as dynamic positioning – to keep them above the dive site while they have people in the water.
When Lemony and Youssus began to repair the pipelines under water, Alcoc watched them from the bell Bibby Topaz & # 39; s the dynamic positioning system suddenly failed. The ship quickly began to move away from the course.
At the bottom of the sea the alarms sounded in the diver's communication system. Lemons and Youasa were instructed to return to the bell. But when they began to follow the umbilical cord, the ship had already returned to the high metal structure they were working on, which meant they had to climb over it.
We had this strange moment when we looked into the eyes of others – Chris Lemon
As they approached the top, however, the cord of Lemony was pressed against a piece of metal protruding from the structure. Before he could release him, the ship that wore it pulled him and dragged him into the metal beams.
"Dave realized something was wrong and turned around to come back to me," says Lemony, whose story has been turned into a documentary "Last Breath." "We had this strange moment when we stared at the eyes of others. He desperately struggled to get to me, but the boat pulled him away. Before I knew, I did not have gas because the cable was so stretched.
The strain on the cable must have been enormous. Composed of a plurality of hoses and electric wires with a rope running through the middle, it creaked as the floating boat pulled it harder and more tightly. Lemons instinctively turned the button on their helmet to start the flow of gas from the emergency tank on their backs. But before he could do anything else, the cable opened and sent him back to the seabed.
Miraculously, in the dark darkness, the lemons managed to get upright and feel the way back to the structure of the well, once again climbed to the top in the hope of seeing the bell and returning safely.
Without oxygen, the human body can survive only a few minutes before the biological processes that feed its cells begin to fail
"When I got there, the bell could not be seen anywhere," says Lemony. "I made a determined decision to calm down and save my little gas I had. On my back I only had about six to seven minutes of emergency gas. I did not expect to be saved, so I just hit a ball. "
Without oxygen, the human body can survive only a few minutes before the biological processes that feed its cells begin to fail. The electrical signals that power the neurons in the brain decrease and eventually stop completely.
"Oxygen loss is right at the sharpest end of survival," says Mike Tipton, head of the Extreme Laboratory at Portsmouth University in the UK. "The human body does not have a lot of oxygen – maybe a few liters. How it is used depends on your metabolism.
An adult on vacation usually uses between a fifth and a quarter liter of oxygen every minute. This can be increased to four liters every minute if it is difficult to exercise.
"If someone is stressed or panicked, it can also increase their metabolism," adds Tipton, who studied people who had long periods without air under water.
They watched helplessly as the movement of the Lemons gradually stopped and his life faded
He returned to Bibi Topaz, the crew desperately trying to manually return to a position to save his lost colleague. As they moved away, they launched a remote-controlled submarine in the hope of finding it.
When they did, they watched his cameras helplessly as the Lemon's movements gradually stopped, his life weakening.
"I remember that I took the last pieces of air out of the tank on my back," says Lemony. – More effort is needed to suck up the gas. He felt a bit like the moments before you fell asleep. It was not unpleasant, but I remember feeling angry and apologizing to my fiancé Morag very much. I was angry at the damage she would have to other people. Then there was nothing.
It took about 30 minutes before Bibby Topaz's crew could regain control and restart the failed dynamic positioning system. When Youasa reached the lemons on the top of the underwater construction, his body was stationary.
By pure will, Jousa dragged her fallen colleague back into the bell and handed it over to Alcov. When they took off his helmet, the lemons were blue and did not breathe. Allcock instinctively gave him two breaths of mouth-to-mouth resuscitation.
Miraculously, the lemons breathed into consciousness.
Common sense implies that he must have died after so long at the bottom of the sea
"I felt very dirty and had flashing lights but I do not have very clear memories of awakening," says Lemony. "I remember Dave sitting on the other side of the bell, who looked exhausted and did not know why. Only a few days later I realized the seriousness of the situation. "
Nearly seven years later, Lemons are still confused how it can survive for as long without oxygen. Common sense implies that he must have died after so long at the bottom of the sea.
But the North Sea cold water seems to have played a role – about 100m (328ft) down, the water probably was below 3C (37F). Without the hot water flowing through the umbilical cord to warm up the suit, his body and brain will quickly cool down.
"Rapid cooling of the brain can increase survival time without oxygen," Tipton says. – If you lower the temperature by 10 degrees, the metabolism decreases by half to one-third. If you lower your brain temperature to 30 degrees Celsius (86F), it can increase your survival time from 10 to 20 minutes. If you cool the brain to 20C (68F), you can get an hour. "
The pressurized gas, which the divers of saturation usually breathe, can give Lemons an extra chance. By inhalating high levels of oxygen under pressure, it can dissolve into the blood stream, giving the body extra reserves to draw.
Divers are probably the most likely people who experience sudden loss of air. But there are many other situations in which oxygen delivery can be cut off. Firefighters often rely on breathing apparatus when entering smoke-clad buildings while high-powered pilots use respiratory masks.
At the less extreme, lack of oxygen – known as hypoxia – can affect many other people. Mountain climbers experience low levels of oxygen when on high mountains, a condition often accused of accidents. When oxygen levels fall, brain function can suffer, resulting in poor decisions and confusion.
Patients undergoing surgery are also often subject to mild hypoxia, which is thought to affect their recovery. Impacts are also caused by the patient's brain, roasted by oxygen, resulting in cell death and damage that can have a lasting effect on their lives.
"There are many diseases where the last stage is hypoxia," Tipton says. "One of the things that happens is that people who are hypoxic begin to lose their peripheral vision and eventually look at one point. It is believed that this is the reason why people report that they see light at the end of the tunnel in the near death experiences.
Kids and women are more likely to survive because they are smaller and their bodies tend to cool down much faster – Mike Tipton
The lemons themselves survived without oxygen without their time. He found only a few bruises on his feet after the test.
But his survival is not unheard of. Tipton has looked at 43 individual cases in the medical literature of people who have been immersed in water for long periods of time. 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 down much faster," Tipton says.
Teaching divers diverses like lemons can also be inadvertently teach their bodies to deal with extreme situations. Researchers from the Norwegian University of Science and Technology (NTNU) in Trondheim have found that divers of saturation are adapting to the extreme environment in which they work by altering the genetic activity of their blood cells.
"We have seen a remarkable change in genetic programs for oxygen transport," said Ingrid Eftedal, head of NTNU's Barometry Research Group. Oxygen is worn around our bodies in hemoglobin, a molecule found in our red blood cells. "We have detected the activity of genes at all levels of oxygen transport – from hemoglobin to production, and the activity of red blood cells is reduced during saturation," adds Ephdental.
She and her colleagues believe that this may be a response to the high concentrations of oxygen that they breathe while underwater. It may be possible to delay the transport of oxygen in the Lemon's body to allow it to make its longer, shorter deliveries.
Pre-dive exercise is also proven to help reduce the risk of bending.
Surveys of local people who usually dive freely without additional air also showed how much the human body can adapt to life without oxygen. People from Bajau in Indonesia can reach a depth of 70 meters (230 feet) while they hold their breath while hunting for spear-feeding.
Melissa Ilardo, an evolutionary geneticist from the University of Utah, has found that Bajau are genetically evolved to have spleens that are 50% larger than their neighbors on the ground, Saluan.
With the larger spleens, Bajau is believed to benefit from a larger injection of oxidized blood and can hold on to breathing for a longer time.
It is believed that the spleen plays a key role in allowing people to dive freely.
"There is something called a mammal's reflex reflex, which is triggered by the combination of breath-holding and water-immersion," said Ilardo. "One of the effects of the diving reflex is the squeeze of the spleen. The spleen acts as a reservoir for oxygen-rich red blood cells, and when it shrinks, these red blood cells are pushed into the circulation to provide an oxygen boost. You can think of a biological diving tank. "
With the larger spleens, Bajau is believed to benefit from a larger injection of oxidized blood and can hold on to breathing for a longer time. A diver from Bajau, who met Ilardo, told her he had spent 13 minutes under water.
The lemons themselves returned to dive about three weeks after their accident – the place where they happened to complete the work they had begun. Marry Morage and they have a daughter together.
Reflecting on his brush with his death and miraculous survival, he does not take much credit for his own actions.
"One of the biggest reasons for my survival was the quality of the people around me," he says. – Actually, I did very little. That was the professionalism and heroism of both of you in the water with me and everyone on the ship. I was very happy.
His incident has caused a number of changes in the diving community. Now they use emergency tanks that carry 40 minutes of air, not five. Now the buds are decorated with fairy lights so they can be seen more easily under the water.
Changes in his own life are not so dramatic.
"I still have to change diapers," he jokes. But he discovers that he thinks of death differently. "I do not see him as something to be afraid of anymore. This is more about what you leave behind. "
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