Harrison Okene was sitting on the toilet – surely the worst place to be as disaster strikes – when a freak wave hit the tugboat he was working on, and turned it upside down. Now he was on the floor, and the toilet was above him.

“I was trying to open the door to get out, when the toilet fell and hit me on the head,” he says. He just had time to see blood pour from the wound before the lights went off. “Everywhere was dark.” The bathroom began to fill with water. “It didn’t take long,” he says. “One minute, two minutes” – and he felt the boat touch the seabed. Thirty metres (100ft) below the surface, it came to rest.

Okene himself doesn’t use the word “disaster” to describe the events of 26 May 2013, and the extraordinary days that followed. He has come to view the experience very differently. He had always loved water, and as a child dreamed of a house by the sea. He loves it even more now.

Okene was going about his usual morning routine when “the incident”, as he calls it, took place. He was 29 and working as a cook on Jascon-4, a tugboat that was assisting an oil tanker about 20 miles off the coast of Nigeria. There had been storms, a swollen sea. The tug had been helping to stabilise the tanker. Okene had got up and said his prayers, as he did every morning, and headed to the galley to turn on the hotplates for breakfast. He hadn’t yet dressed, and was wearing only his boxers. He was due to go on leave in three days; he was thinking about this as he headed for the bathroom, and the wave hit.

Water began to fill the cubicle. Okene panicked as he struggled to open the door. When he finally emerged into the watery darkness, he had no idea which way he was facing. The propellers were up, the wheelhouse was down. Port and starboard no longer held much meaning. In the alley to the watertight door – an exit hatch – he met two, or possibly three of his colleagues. As the water level inside the boat rose, they battled with the hatch.

“I did not have the patience to wait,” Okene says. In a move that surely must run counter to every instinct, he turned away from the exit, and swam further inside.

Okene’s story of survival is partly about his faith and fortune. But it is also a story of quick decision-making and extraordinary enterprise. Because as he swam away from the closed exit, the force of the water swept him into another toilet, this one attached to the second engineer’s cabin. The door had shut as he was swept in and the water level rose, but the bathroom did not fill completely.

The crew routinely kept all the cabin doors shut, because of the threat of pirates. “The air couldn’t go out of the boat completely. Some had to be trapped inside,” Okene says. He kept his head in the small pocket of air below the ceiling – which was, in reality, the floor – clinging to the base of the washbasin.

Shut away in the dark he heard “so many shouts, shouts, shouts” – his colleagues “calling and crying”.

At this point, Okene still regarded the exit hatch as his best route to freedom. In an effort to leave the bathroom, he broke the handle of the door. “But I told myself, instead of panicking, you have to think of a way out.” From this moment on, he fostered in himself a kind of hyper-composure.

Okene says he has always been practical. He was “among the youngest” of 13 children and his mother regarded him as a helper. He used to carry the vegetables with her to sell at the market in Warri, where they lived. Now, practicality was how he would persuade himself that he was “in charge of the situation”. Spotting a vent, he broke it, and used a piece of the vent’s steel to prise open the door and free himself. As he worked, “one after another”, the shouts of his colleagues fell silent. “I couldn’t hear them any more.” He assumed they had escaped.

When Okene opened the door and entered the second engineer’s cabin, he saw two lifejackets, each with a torch. He put one torch in his mouth, the other in his boxers, and swam back to the watertight door again to try to escape. Outside the second engineer’s cabin, the corridors were full of water, there was no air pocket, and he did not have enough breath to work away at the exit door for long.

Again and again over the following minutes and hours, he returned, swimming between the safety of his air pocket and the watertight door. The first time, he almost missed his way back to the safety of the second engineer’s bathroom – there were so many doors: the engine room, chiller, mess room. “If you got stuck in any room, you were lost. It was totally dark, I was confused. If you don’t act fast, you can lose your life there,” he says. Later, he learned that one of his colleagues had entered the mess room and drowned.

Again, Okene focused on practicalities. Searching through bags, he found a tin of sardines, a can of cola and some loose coveralls. He tore the covers into strips, and tied the strips together into a rope. He secured one end of it to the door of the cabin. Now, when he got tired at the watertight hatch, “I could use the rope to guide myself back.”

The water was very cold, so next Okene ripped the wooden panels from the ceiling and tied them together into a little raft. Now he could sit up there in his tiny air pocket, and figure his way out of the wreck and the door that would not budge.

In total darkness and silence, Okene found himself in a strange moment, in a place beyond all maps of human survival. It was as if he had passed into a parallel world with only a faltering sense of time and little to cut through the sensory deprivation, other than the muffled hum of vessels moving through the ocean nearly 30 metres above him. Now Okene understood that he must not leave his base. To open the watertight door seemed impossible. “So I had to keep my mind away from that. ‘Let me just stay put,’ I thought.”

He had consumed so much salt water on his forays that his throat throbbed and his tongue peeled. He ate the sardines and drank the cola, while crayfish made a supper of his body. He could feel them biting his legs, torso and arms, making new wounds. And all the time, the water level was rising. Okene thought of his mother, and of his wife. “How is she feeling? How will the world treat her? I had access to nothing. Everything was thoughts and memories before my eyes.” He prayed, and sang – “so many church songs. ‘Father we cannot see you, but we can see your wonders,’” he sings again now, down the phone.

“I tried to kill the fear in front of me. Because one thing that can kill you fast is fear. That panic that comes at you, it kills you before your real death comes. Because the moment you start panicking, you use too much oxygen.”

When a different sound – closer to him – disturbed the silence, Okene had no idea that a diver had come to put a marker buoy on the vessel to warn other traffic of the wreck’s location. He hammered in hope on the side of the boat, “trying to get a signal to the person outside”.

He has no idea how many hours or days afterwards he became aware of a tiny disturbance in the darkness – “a reflection of light like a bubble”. He left his raft to try to find the source of the light, failed, returned, filled his lungs with what little oxygen was left, and looked again. This time he saw the diver, swimming on a long umbilical.

Video from the camera on the diver’s helmet shows the moment that the diver saw Okene’s pale palm floating in the water before him. The diver relays to base that he has found another body. And then Okene’s hand grabs his.

First, Okene was taken to the divers’ bell, and from there to a recompression chamber where he would spend a further three days; he would have died if he had returned straight to the surface. He could not believe it when the rescue team told him that he had been underwater for nearly three days. He had no sense of having passed even a single night.

Incredibly, when Okene’s vital signs were measured, he says: “Everything was normal. My temperature, blood pressure. I thought, that’s not normal.”

Released from the recompression chamber, he shunned advice to go to hospital. He was desperate to get home. But over the next few weeks, media teams gathered at his front door, and the nights were besieged by dreams. As he slept, he “felt the bed sinking. I would pick up my wife, carry her, and try to open the door to get out,” he says.

They went to the Gambia for a break. A hotel on the seafront might sound like the worst place to recover, but for Okene, the ocean had always been “a very peaceful place”. He swam, in the pool, in the sea, and when he got back to Nigeria, he says, “I was OK.”

But in many ways, the hardest part now began. Okene had to reconfigure his understanding of his place in the world, his life. He saw a psychologist, “but she was not saying anything that made sense to me”. He felt himself adrift.

Again, an accident provided a turning point.

***

The year after the Jascon-4 sank, Okene was driving to work with a friend when his car went off a bridge and into the water in the city of Port Harcourt. “When I opened my eyes, my four tyres were up.” He swam out of the car, only to realise that his friend was still in the passenger seat. He swam back to bring him out. Neither had sustained injuries, so they went to the police station, where they were told the car had to be removed from the water.

“So I went down into the water again to put the rope around the car and bring the car out. After that I told myself: ‘What are you afraid of? How can you be scared? You have seen so much. If you have come through this, I think you should not be afraid of anything.’”

Okene wanted to train as a diver, but his older brother, worried for his wellbeing, counselled against it. In 2015, Okene and his wife separated. “I was alone. I didn’t have children, I didn’t have a wife. Not a good job. I was frustrated. Just alone with my dog. I was depressed, but nobody knew,” he says.

Okene sounds more scared of this experience than of his time underwater. He felt he would die if he didn’t act. “If I had sat down and said: ‘I’m not going to the ocean again’, I would not be here today.” He enrolled on a three-month diving course, and told his brother when he had completed it.

“I have faced a lot of my fears in my life, and I decided to face this once and for all,” he says. “I know it should be my fear, but I don’t need to be scared of water. Because I need to embrace my fear once and for all and be strong. Our happiness, our joy, our future – they are all in our hands. I had to reprogramme my thinking. I balanced my mind,” he says

Eight years on, Okene, now 39, works as a diver, installing, constructing and making repairs to oil and gas facilities; he is on his dive vessel as we speak. “The maximum depth I can go to now is 50m,” he says. He has a partner, and three children. His experience underwater, and his survival “have changed my life in so many ways. The way I think, the way I see life. And, yes, improved my life actually,” he says. “I know there is a God, and there is a God beside me. I know he has a great purpose for me. I always feel so comfortable and guide myself. I try not to offend anybody and I try to trust life, because when humans are close to death, that is when they understand … We are all one.” Meaning comes from “the lives you touch”.

Okene has a house by a lake now, but it is not quite where he wants to be. “If I have the money, I am going to buy a house beside the ocean.”