The first dive to a depth of a thousand feet was made in 1962 by Hannes Keller, an ebullient twenty-eight-year-old Swiss mathematician who wore half-rimmed glasses and drank a bottle of Coca-Cola each morning for breakfast. With that dive Keller broke a record he had set himself one year earlier, when he briefly descended to 728 feet. How he performed these dives without killing himself was a closely guarded secret. At the time, it was widely believed that no human being could safely dive to depths beyond three hundred feet. That was because, beginning at a depth of one hundred feet, a diver breathing fresh air starts to lose his mind.

This condition, nitrogen narcosis, is also known as the Martini Effect, because the diver feels as if he has drunk a martini on an empty stomach—the calculation is one martini for every additional fifty feet of depth. But an even greater danger to the diver is the bends, a manifestation of decompression sickness that occurs when nitrogen gas saturates the blood and tissues. The problem is not in the descent, but the ascent. As the diver returns to the surface, the nitrogen bubbles increase in size, lodging in the joints, arteries, organs, and sometimes the brain or spine, where they can cause pain and potentially death. The deeper a diver descends, the more slowly he must ascend in order to avoid the bends.

In 1956 a Royal Navy boatswain had successfully dived to six hundred feet, breathing a mixture of helium and oxygen to avoid nitrogen narcosis, but he took twelve hours to resurface. Keller, by comparison, returned to the surface after his first record dive in less than an hour. He boasted of using “secret” mixtures of gases for his underwater breathing apparatus, with different mixtures designed for different depths, but wouldn’t disclose exact figures. After an editor from Life, who had accompanied Keller on his 728-foot dive, wrote an article about their accomplishment, the US Navy took interest. So did the Shell Oil Company.

The Navy gave Keller $22,000 to finance the thousand-foot dive. Shell provided an experimental offshore drilling ship called the Eureka and a decompression chamber; at the time Shell had already begun to drill offshore, but only to a depth of 250 feet. Keller chose as his diving partner another journalist, Peter Small, the thirty-five-year-old editor of Triton magazine (now Diver) and a founder of the British Sub-Acqua Club. The dive took place in Southern California, off Santa Catalina Island; Keller and Small planned to be the first men to set foot on the Continental Shelf. Observers aboard the Eureka included several officers from the US Navy’s experimental diving program; a group from Shell Oil; two young safety divers; and Mary Small, Peter’s twenty-three-year-old wife. The Smalls had been married less than three months earlier.

Shortly before noon on December 3, the men entered a diving chamber called the Atlantis, which Keller had designed and built. It was seven feet high and four and a half feet in diameter, with a bottom hatch through which the divers could exit. The Atlantis was connected to the Eureka by various cables, one of which allowed the observers to watch the divers on closed-circuit television. It took sixteen minutes for the Atlantis to descend one thousand feet, including breaks for the divers to check equipment and switch air mixtures. At the bottom, five feet above the seabed, Keller left through the hatch. He was armed with two flags, Swiss and American, which he planned to plant on the ocean floor.

But as soon as he exited into the dark water, the fabric of the flags became entangled with his breathing hoses. He couldn’t see. It took him two minutes to free himself of the flags, at which point he returned to the diving chamber, exhausted and dizzy. In his confusion Keller didn’t realize that one of his swim fins had become stuck in the hatch, preventing it from closing properly. When he figured out that his special mixture of gas was leaking, and that there was not enough to sustain them for the ascent, he switched to regular air, and the two men instantly passed out.

The crew aboard the Eureka pulled the diving chamber to a depth of two hundred feet, and the two safety divers went to investigate. They found that the chamber was losing pressure, but were unable to seal it. When one of the divers, a UCLA undergraduate and friend of Small’s named Chris Whittaker, resurfaced, his face was bloody. He appeared dazed. Against the advice of the support crew Whittaker and his partner made a second dive to retrieve Small. The other diver cut away the fin, allowing the hatch to seal, but Whittaker did not return. His body was never found.

Once sealed, the Atlantis was pulled to the surface. Both Keller and Small recovered consciousness. For six hours they remained within the chamber while the air pressure was gradually decreased. Keller, apart from experiencing oxygen hallucinations for thirty minutes, reported few ill effects. Small slept fitfully. After several hours Keller noticed that Small had stopped breathing. His mouth was foaming. The chamber was opened, and Small was rushed to a Navy hospital ship, but it was too late. A coroner determined that the cause of death was decompression sickness. Small’s tissues and organs were riddled with gas bubbles.

Nevertheless Keller had managed to validate his theory. Life ran a follow-up article that included an interview with Kenneth MacLeish, the editor who had accompanied Keller on the earlier dive. “The concept was brilliant; perhaps its implementation was not,” said MacLeish, in a rather gruesome understatement. He continued:

Keller will go on with his work and every serious diver and student of the sea must be glad of that. His method will help open up the seas to the free diver, unencumbered, unenclosed, able to reach out and touch…and the human animal will extend still further his unique ability to go where he is not designed to go.

MacLeish was more prophetic than he knew. When executives at Micoperi, an Italian company that specializes in marine construction, read about Keller’s achievement, they urged Shell to provide him with additional funding. The two companies worked together to build new facilities for Keller to continue his experiments, forming a joint-venture company called Sub Sea Oil Services. During the next twenty years, Shell’s divers would descend as deep as 1,900 feet. The free diver would revolutionize the oil industry, allowing human beings to extract oil in many places where they were not designed to go.1

Mary Small, widowed at twenty-three, would take no solace in this. When she was interviewed by a reporter right after the Catalina tragedy, she called her husband’s death “just one of those diving accidents.” But nine weeks later she committed suicide. She was found at her London home, photographs of her husband strewn on the floor around her, in a room filled with gas.

Today it is an economic and even geopolitical necessity for oil companies, in order to maintain pipelines and offshore rigs, to send divers routinely to depths of a thousand feet, and keep them at that level of compression for as long as a month at a time. The divers who do this work are almost entirely male, and tend to be between the ages of twenty-five and forty. Were they any younger, they would not have enough experience or seniority to perform such demanding tasks. Any older, and their bodies could not be trusted to withstand the trauma. The term for these extended-length descents is “saturation diving,” which refers to the fact that the diver’s tissues have absorbed the maximum amount of inert gas possible.

The industry is currently in the midst of an expansion that originated in 2005, after Hurricanes Katrina and Rita together destroyed more than one hundred drilling platforms in the Gulf of Mexico and compromised another fifty; the storms also damaged nearly two hundred pipelines, contributing to four hundred incidents of pollution. Remotely operated vehicles could only assess and repair some of the damage, so much of the work had to be done by divers. Wages increased accordingly, and since then, as the oil industry has drilled in increasingly deep waters, demand for divers has continued to grow.

Not everybody is cut out for the job. A diver cannot be claustrophobic or antisocial, because he must spend much of his time in a tiny sealed capsule with several other divers. He must be well-disciplined and perceptive, for he is likely to encounter a variety of unexpected hazards on the job. Many divers are military veterans, or have worked as roofers or mechanics. “The best are those who have a great deal of confidence in themselves and their abilities,” one former diver, Phil Newsum, told me. “You have to be willing to adapt to any situation. Philosophically, when you go out on a dive job, you’re expecting something is going to go wrong.”

Often, because of the depth, the job is performed in the dark, with only a headlamp to light the way. Divers have told me stories of sudden encounters with manta rays, bull sharks, and wolf eels, which can grow eight feet long and have baleful, recessed eyes, a shovel-shaped snout, and a wide, snaggletoothed mouth. One diver sent me a video, filmed from a camera in the diver’s helmet, of an enormous turtle that was playing a game of trying to bite off the diver’s feet and hands every few minutes. The diver finally sent the animal swimming away by pressing a power drill to its head. Someone else sent me a photograph of a diver riding a speckled whale shark, as if on a rodeo bronco.

Newsum, who is now the director of an industry group called the Association of Diving Contractors International ( ADCI ), estimates that only three of every fifteen people who graduate from commercial diving school are able to withstand the rigor of the profession for a full career. Many are enticed by the high salaries, but few can endure the job’s physical and psychological toll. Those who stick it out tend to do so out of a passion for the job’s eccentricities.

The life of a commercial diver is somewhat less stable than that of a traveling salesman or mercenary soldier. He does not make his own schedule and has little control over his own fate, which is one reason why divers between jobs have a reputation for, as Newsum puts it, “living hard.” The diver never knows when his next job will come, but as soon as he gets called for an assignment, he must head directly to the nearest port or helicopter pad. A successful diver will work offshore about 160 days a year, cumulatively. A job might last a day, or two months. Work is most consistent, at least in the Gulf of Mexico, in the warmer months, from late March through November, but hurricane season falls within that period. Hurricanes are a mixed blessing—they disrupt ongoing jobs, but they create new ones.

Divers work not for oil companies but for private contractors, which range from smaller, independent operations to larger, publicly traded companies like Cal Dive, Helix Energy Solutions, and Oceaneering. These larger contractors have their own training processes for saturation divers that are often more rigorous than what is mandated by federal law. There is a general touchiness in the industry about safety, especially since the BP Deepwater Horizon tragedy. Shell or ExxonMobil is unlikely to hire a contractor with a reputation for carelessness.

Most offshore divers aspire to work saturation jobs (“Sat is where it’s at,” says Newsum), but after graduating diving school and passing an extensive physical, a diver must begin as a “tender,” or apprentice diver. A tender will serve on the support staff for deeper divers, and work at depths as shallow as four feet of water. Often a tender will assist on jobs involving oil pipelines, which tend to be buried four to six feet below the mud line in order to avoid contact with ships or marine life. A tender might be called upon to bury a repaired pipe, using hand jets to displace the bottom so that the pipe will sink belowground. Or he might excavate a pipe, in preparation for a more experienced diver to repair it. An apprentice makes about $40,000 a year.

The deeper you dive, the more you get paid. In his second or third year an apprentice may be promoted, or “broken out,” to a full-time diver. His salary will increase to between $60,000 and $75,000. He will start as an “air diver,” diving as deep as 120 feet while breathing regular air. Jobs at this depth might include retrieving tools from the worksite, or cutting and retrieving the polypropylene cord that runs between the surface vessel and the underwater worksite. Next the diver will be assigned to more complex jobs below a hundred feet, for which he must breathe mixed gas in order to avoid suffering the effects of nitrogen narcosis while working with heavy machinery. A full-time mixed-gas diver can earn more than $100,000 a year. He will perform jobs at ever greater depths, with higher degrees of technical difficulty, until his diving supervisor deems him ready to graduate to saturation diving. Sat divers can make $200,000 a year. Sat’s where it’s at.

A saturation diving complex looks like a small space station. It comes in different sizes, accommodating six to twenty-four divers. A typical complex, which sits on the deck of a ship or an oil rig, has four main components. The first is the living chamber, which resembles a train’s sleeper car, or the berth of a submarine, and has double-decker cots with fire-retardant mattresses and a sitting area with a television screen. (Larger systems have two or even four separate living pods.) A camera—often referred to as “big brother”—peers through a porthole, observing the divers. Other portholes, covered with plexiglass, allow the marooned divers to glimpse the outside world.

By crawling through a short tube from the living chamber you reach the transfer lock, a small capsule that contains a toilet, a small sink, and a showerhead. At the top of this chamber is a hatch that leads to the diving bell, which can take the shape of an amphora, an orb, or a squat cylinder. The diving bell is encased within an exoskeleton of pipes, which are responsible for lifting it to and from the complex. Another portal leads to the hyperbaric rescue chamber, the equivalent of a lifeboat, which has enough breathing mixture to last the crew for three days. On newer, more technologically sophisticated ships, the saturation complex is built into the body of the vessel, below-decks. On these models the diving bell drops into the water through an opening in the bottom of the ship, called a moon pool.

Once the divers are sealed inside the saturation complex, the air pressure is increased until it matches the pressure at the job’s working depth—this generally takes about a day. The breathing mixture inside the complex is also adjusted accordingly—the deeper the job, the more helium will be added to the breathing mixture. (Helium, besides allowing divers to avoid the risk of nitrogen narcosis, is easier to breathe under pressure because of its low density; it is also more quickly flushed from the organs and tissues than heavier gases.) This causes the divers to sound like Donald Duck, or children who have inhaled helium from balloons at a birthday party. But a diver inside the system doesn’t always realize that he sounds like Donald Duck, because the other members of the crew also sound like Donald Duck.

This condition is known as “helium ear.” The diver must often be reminded to enunciate his words when he speaks through the intercom to the supervisors and life support technicians who monitor him from outside the complex. Saturation systems often come equipped with a Helium Speech Unscrambler, a device that slows down the speed of the divers’ voices. One company that manufactures these devices boasts of their ability to correct a diver’s “raw helium speech to normal intelligible voice levels.”

Food is delivered to the crew through the medical lock, a small passageway that serves as the vessel’s mouth. The med-lock is clamped on either end. Before the divers retrieve their meal, it must be “blown down” to the same pressure as the rest of the complex. Changes in pressure affect one’s sense of smell, so meals tend to taste bland. Some types of food, particularly those with air bubbles, do not withstand compression. Carbonated beverages turn flat. Rice Krispies collapse. Pancakes wrinkle up. Certain materials break down as well; Styrofoam, for instance, will shrink, or implode.

All jobs at a depth of three hundred feet or deeper are required by law to use a saturation system, but it often makes financial sense to use one at shallower depths for more involved jobs. A diver using mixed gas cannot remain deep for a long period of time, for these dives require many hours of decompression and recovery. Saturation divers, on the other hand, can work full eight-hour shifts, and must only undergo decompression once, when it is time to leave the complex. Saturation gas diving can be cheaper, even at lesser depths, for the helium gas that divers inhale, which is expensive, is not wasted but recycled. In a saturation system, exhaled gas is captured by a reclaim system, which sends it through an apparatus that “scrubs” the gas, remixes it with a fresh helium and oxygen mixture, and returns it to the breathing tank. So both the air and the divers are recycled.

Saturation diving also allows work to continue unceasingly until the job is finished. Divers tend to work in pairs, as most diving bells hold two people—a crew of three pairs of men can work without interruption in consecutive eight-hour shifts, making possible twenty-four hours of continuous work. The bell functions like an elevator with two stops—the underwater work site and the saturation complex. Divers can look out of a porthole and watch the light dim as they sink; often by the time the divers reach their working depth—it can take an hour—the water is pitch black. The bell has external lighting panels that function like headlights; these are used to illuminate the working area, which might be an old platform that needs to be dismantled, or a busted wellhead.

The bell is connected to the saturation complex by a large cord that contains within it smaller tubes, which in turn contain breathing gases, electricity, and fiber-optic lines for communication. The divers’ lives depend on this cord, which is called the “umbilical.” Smaller umbilical cords connect the divers’ breathing suits to the bell. There is a video camera in each diver’s helmet, and a microphone that allows the diver to communicate with his supervisor. (Supervisors tend to be former saturation divers who have aged out of the job.) Because the water at these depths is close to, or even below, freezing, a tube pumps warm water, collected from the surface of the ocean, into the diving suit. This turns the suit into a personal hot tub. There is an oft-repeated cautionary tale, likely apocryphal, about a diver whose air hose vacuumed up a jellyfish from the ocean surface and pumped it down into his suit, the angry jellyfish getting trapped in the crack of his ass.

When the job is finished, the divers can’t simply leave the complex. They must first decompress. The formula is one day of decompression for every hundred feet of depth, plus an extra day, which means that a crew saturated at a depth of a thousand feet must wait eleven days before they can leave. (Divers rarely work below a thousand feet, the point at which they become susceptible to high-pressure nervous syndrome, which can result in nausea, vomiting, tremors, and neurological damage.) During the decompression period, the pressure in the saturation complex is reduced gradually, with many rests along the way, so that the body doesn’t undergo shock. The breathing mixture is changed as well, until, by the final day, the divers are breathing normal air. Upon exiting the saturation complex, they are given a full physical examination and kept under observation for twenty-four hours. They must wait seventy-two hours before they can board an airplane.

If a saturation crew is already in the Gulf, their contractor will look to attach them to another job if possible. It’s always cheaper for an oil company to hire a crew that is already at sea rather than fly a new crew out from the mainland. So with any luck, the crew may be resealed inside a saturation chamber within days.

Commercial diving remains a dangerous job, but not for the reasons that haunted early experimenters like Hannes Keller. Whether saturation diving has long-term repercussions for human health remains a subject of cantankerous debate. Some scientific studies have shown moderate impairment in spatial memory, vigilance, and reaction time among those who have worked as saturation divers for more than three and a half years. One such study was cited by the government of Norway in 2000, when it decided to award several million dollars in workers’ compensation payments to sat divers who had worked in the North Sea oil industry between 1965 and 1990.2 More than a decade later, there is still no scientific consensus on the residual health effects of saturation diving.

The work itself, however, is extremely dangerous. A CDC report in 1998 estimated that the occupational fatality rate for commercial divers was forty times the national average for all workers, at an annual rate of 180 deaths per 100,000 employed divers. These numbers have declined slightly in the last decade, in which, according to the US Coast Guard, nineteen commercial divers have died offshore. An additional twenty-four workers died diving inshore, which involves work in lakes, rivers, or coastal harbors, and relies primarily on scuba diving. That comes out to an annual fatality rate of approximately one per every thousand divers, or twenty-eight times the national average.

This makes commercial diving the third-most-dangerous occupation, behind fishing and logging. Very few of those deaths can be attributed directly to decompression-related illnesses. Instead divers are threatened by the same hazards that confront all occupations that require the use of heavy machinery, only a diver’s risk is multiplied by the dangers of performing the work underwater, with limited vision, while encased in a diving suit.

Most divers have horror stories. Paul Spark, who is currently a supervisor on a dive support vessel in the North Sea, worked as a diver for twenty-nine years. During his very first dive, in 1977, to repair a blow-out preventer 410 feet below the surface, his diving bell flooded with water, almost drowning him and his partner. Later he was very nearly crushed by a thousand-pound blind flange, a plate used to seal the end of a pipe; a “rather large wolffish” bit his foot, drawing blood; and while performing salvage work on the Kursk, the nuclear-powered Russian submarine that sank in the Barents Sea in 2000, drowning all 118 aboard, there was a loud explosion. Spark had been using a high-pressure water jet to bore holes in the submarine’s pressure hull when it occurred. He was unharmed, and returned, dazed, to his diving vessel. He never found out what caused the explosion.

The list of commercial divers who died internationally in 2012 includes Brad Sprout, a twenty-nine-year-old employee of Global Diving and Salvage, who was killed in the Gulf of Mexico when he dove to remove a net that had been caught in the ship’s gears. Paul De Waal, twenty-seven, died while cleaning the hull of a cruise ship, the Norwegian Star. Pierre Rossouw, twenty-nine, an employee of Underwater Engineering, died of a broken neck in a crane accident. Jarrod Hampton, twenty-two, died on his second day at work for Paspaley Pearls, while diving for wild oyster shells off the coast of northwestern Australia. Felix Dzul, thirty-six, died while diving off the Yucatan Peninsula for sea cucumbers.

While most casualties occur during mixed-gas diving, there are exceptions. On September 25, a saturation diver named Chris Lemons was inspecting a drilling template—a large metal device that guides the drill—in the North Sea’s Huntington oilfield, 115 miles east of Aberdeen, Scotland. The structure was three hundred feet beneath the surface. Lemons’s diving bell had descended from a ship called the DSV Bibby Topaz. While Lemons and his diving partner were conducting tests on the template, the Bibby Topaz’s global positioning system malfunctioned and the ship began to float away with the current, dragging the diving bell with it. Lemons and his partner were pulled off the template by their umbilical cords. The other diver swam back to the diving bell, but Lemons’s cord snagged on the template, and tore off. Five minutes later, the Bibby Topaz had drifted nearly eight hundred feet away, abandoning Lemons alone on the drilling template, without air supply or warm water. He had access to an emergency oxygen supply, but there was only enough in the tank to last him fifteen minutes.

In order to conserve his oxygen, Lemons sat in the middle of the structure and tried, despite the frigid temperatures, to remain as still as possible. When his air supply ran out, he fainted. Another fifteen minutes passed before a rescue diver found Lemons and pulled him into the diving bell. Miraculously, although Lemons hadn’t taken a breath in more than fifteen minutes, he revived. The coldness of the water seemed to have been the crucial factor. By instinct all mammals, when submerged in cold water, suspend or limit nonessential operations in order to conserve energy for survival; this is called the diving reflex. The heart beats slowly, blood vessels constrict, metabolism decreases, digestion stops. Like a computer with failing battery life, the body shuts itself down to preserve what is left of its charge. If Lemons had not lost his hot water tube, it’s doubtful that he would have survived.

During the last five years, a diver’s median wage has increased 50 percent. “Because there are more sophisticated, remotely operated vehicles, everyone wants to believe that diving is being phased out,” Phil Newsum, the director of ADCI , told me. “But there are still many things that need to be done in water by an individual, and that won’t end anytime soon.”

I asked Newsum if he has any regrets about his life work. “You have to pay a price,” he said. “But a lot of folks will spend their entire life looking for one thing that they love, and I’ve found it. Everybody in this industry takes a good deal of pride in that. Whenever I meet new people, they want to know about my job. Nobody ever asks a doctor or lawyer or an IT guy about their job.

“It’s true you get an adrenaline rush—that’s probably what attracted most of us to the industry. But I don’t consider myself a thrill-seeker. My real attraction is to the deep. I’m intrigued by the unknown.” This puts him in the same category as both Hannes Keller and Peter Small, though not, perhaps, Shell Oil.