How did a man trapped in the depths of the sea survive for three days in conditions that surely should have killed him?

Turns out that an air bubble was Harrison Okene's savior.

The Nigerian man had been lost at sea after his tugboat, the AHT Jascon-4, suddenly capsized and sank 100 feet below the surface of the ocean. Okene, a cook, was trapped in a four-foot bathroom with no way to signal for help, no food, no water—nothing, for three long days.

His miraculous survival was filmed six months ago by rescuing divers who had come to collect bodies and instead saw Okene's desperate, outreached hand seeking help. This week, the video has gone viral, bringing international attention to the power of an air bubble.

So how'd that bubble last so long?

Eric Hexdall, a nurse and clinical director of diving medicine at the Duke Center for Hyperbaric Medicine and Environmental Physiology, estimates that in an area of about 13.5 cubic meters—roughly the size of the air bubble Okene was trapped in—a person has about 56 hours before carbon dioxide toxicity sets in.

"If you're trapped in something like that, your carbon dioxide levels will build to a toxic level before you use up the oxygen," Hexdall said, emphasizing that carbon dioxide would be the first problem Okene would have faced, before running out of oxygen.

In addition to Okene creating more trapped carbon dioxide in the course of normal breathing, there is more carbon dioxide under water than on land.

Hexdall said that there are stages of deep sea carbon dioxide toxicity.

"At 50,000 parts per million [of carbon dioxide particles], you see measurable signs of toxicity," Hexdall said, referring to a "buzz" or "high" a person would experience. "At 70,000 parts per million, you lose consciousness pretty rapidly."

Hexdall estimates that Okene began to experience the first symptoms of carbon dioxide toxicity after about 56 hours.

"It wouldn't have necessarily poisoned him," Hexdall said. "It would have taken about 79 hours for him to be unconscious from carbon dioxide."

Okene was rescued after 60 hours of being trapped—right in the window for survival.

Threat of Air Pressure

Okene also managed to elude the threat of high air pressure, which can be deadly under water.

Under increased air pressure, human blood becomes saturated with nitrogen—Okene's nitrogen levels during his ordeal were much higher than ours on the Earth's surface.

Diving deep can bring on "nitrogen narcosis"—when under more than 80 feet of water, a swimmer can become dazed from the overwhelming levels of nitrogen.

Then there's the problem of decompressing to surface air pressure after rescue.

"He can't come back to the surface immediately," said Petar Denoble, vice president of research at the Divers Alert Network. "If he did, he would die."

To get Okene and the divers who saved him back to normal pressure levels, the group had to enter a diving bell, also known as a transfer capsule.

According to Denoble, this vessel would have been "at the same pressure as the bottom of the ocean," allowing for the group to be transported to the surface while maintaining the pressure of the original location.

From the diving bell, Hexdall said Okene and the rescue team probably "[crawled] through a tunnel where it is warm and dry," entering a decompression chamber. This chamber allows people to gradually adjust to normal pressure levels.

Regardless of the science, Hexdall said Okene was lucky to have survived his ordeal: "I don't know what it was—it was divine providence."