There are few jobs more dangerous than deep sea saturation diving, where divers ascend to depths as great as 985 feet (300 meters) to repair subsea structures. On these often month-long dives, divers live in pressurized chambers to keep them from getting decompression sickness. However, at those great depths, sometimes things go awry. Here are 10 deep sea diving accidents that will shiver your timbers.

Related: Top 10 Deadliest Industrial Accidents That Were Avoidable

10 Byford Dolphin Accident

The Byford Dolphin accident is one of the most major deep-sea accidents to have happened. This incident took place in 1983 on the Byford Dolphin, a drilling rig that was operated in the North Sea.

It happened like this. On a normal day at work, two divers climbed into the rig’s diving bell, a transportation chamber to take them down to depth before heading down to the chamber system far below the surface. At first, all seemed to go well, with the divers taking turns resting and heading out to work on the rig.

One fatal day during their time underwater, however, two divers were resting in their decompression chamber while another two divers made their way to the chambers in the diving bell. Everything was going as planned as the two tenders—the “drivers”—secured the bell to the chambers. The two divers on board would soon proceed to their own compression chamber. However, as the tenders were preparing to depart, they failed to seal off the diving bell properly from the chambers before beginning their ascent.

What ensued was that the chambers were suddenly decompressed from nine atmospheres to one atmosphere, and the air rushed out of the chambers. Tragically, three of the divers inside the chambers at the time were killed in a horrible way—through explosive decompression. Essentially, the nitrogen bubbles in their blood expanded, causing them to boil from the inside out. The fourth was sucked out of a very narrow opening, ejecting his internal organs. One of the divers in the bell was also killed in the accident.^[1]

9 Wildrake Accident

The Wildrake accident took place in August 1979 on an oil rig in the North Sea. During this dive, two commercial divers—Americans Richard Walker and Victor Guiel—climbed into a diving bell aboard the MS Wildrake, a support vessel on the oil rig.

Unfortunately, the diving bell became separated from the lift wire that was used to lower it and pull it up while the bell was at a depth of 525 feet (160 meters). That meant that there was no electricity or heat supplied to the diving bell.

The oil rigging company did its best to rescue the two divers who were inside the diving bell, but their attempts would take nearly twenty-four hours. In that time, the fate of the two divers in the bell was sealed—by the time the rig managed to pull the diving bell back to the surface, the pair of divers had passed away due to hypothermia.^[2]

8 DOF Subsea Accident

Not all diving accidents have occurred in the North Sea. One nasty deep sea diving accident that occurred took place in 2017 off the northeastern shore of Australia and was run by a company called DOF Subsea Australia.

In this particular accident, DOF Subsea Australia sent several divers down between 778 and 885 feet (237 and 270 meters) to work on an underwater pipeline. This was actually one of the deepest saturation dives in Australian waters, which meant that it was a pretty big deal.

Unfortunately, it seems that the company didn’t see this dive as a big deal. They failed to give their divers the proper gases needed to work at those depths. When the divers returned to the surface, they began complaining of hallucinations, tremors, and cognitive issues, stating that they’d even noticed these symptoms setting in while they were on the ocean floor.

Upon further investigation, it turned out that the divers were suffering from high-pressure nervous syndrome, which takes place due to divers breathing helium at deep depths. While the symptoms were reversible and the divers didn’t suffer any permanent health issues, DOF Subsea Australia was court-ordered to pay for their negligence.^[3]

7 Drill Master Accident

The Drill Master accident occurred in 1974 in Norway and was a tragedy that wound up costing two commercial divers their lives. In this particular accident, the two divers in question, Per Skipnes and Robert John Smyth, were getting ready to work on a rig called the Drill Master.

While inside the diving bell at a depth of 321 feet (98 meters), the drop weight on the bell malfunctioned and was released. This caused the diving bell to go shooting up to the surface.

Now, it would have been bad enough if that was all that happened. However, the bottom door of the diving bell was open at the time. This meant that when the rig shot up to the surface, the pressure in it changed rapidly, and both divers wound up dying due to decompression sickness and drowning.^[4]

6 Star Canopus Accident

The Star Canopus accident took place in Scotland in 1978 and was part of a routine dive alongside the Beryl Alpha platform out in the North Sea. On this particular dive, two divers named Lothar Ward and Gerard Prangley climbed into the diving bell to head down for a routine dive.

Unfortunately, the drop wire, life support, and guide wires were all severed by a loose anchor. Instead of slowly lowering the diving bell to depth, the bell plunged down to a depth of more than 328 feet (100 meters).

A rescue mission was launched, and more than thirteen hours later, the two divers were finally recovered. Tragically, by that time, they had both passed away due to drowning and hypothermia.^[5]

5 Stena Seaspread Accident

The Stena Seaspread accident took place in the North Sea in 1981. During this accident, two divers named Phil Robinson and Jim Tucker were more than a hundred meters below the ocean surface in a diving bell, having just completed work on the oil rig.

Although all seemed to have gone well, what the team didn’t know was that strong tides had damaged the umbilical cords to the bell, which meant that the diving bell was no longer receiving air or pressure.

Of course, as soon as the surface team realized what had happened, they set about launching a rescue operation. They began pulling the diving bell up to the surface. However, they realized that the bell had lost pressure and that the divers were at risk of decompression sickness.

The rescue team, thinking fast, lowered a second dive bell to the divers’ depth, and rescue divers helped move the two men from the broken bell into the new one. The rescue was a success, and all parties involved made it back to the surface unharmed.^[6]

4 Venture One Accident

Part of another seemingly routine dive, the Venture One diving accident, took place in 1977 in the North Sea. In this particular accident, two divers named Dave Hammond and Craig Hoffman were set to lower a blowout preventer to 525 feet (160 meters) for the Venture One drilling rig.

As part of the operation, the divers had to cut several loose wires on the blowout preventer. Hoffman waited in a chamber in the diving bell while Hammond went out to work on the rig. It was while Hammond was working on the rig that a strange electrical sound was heard over the communications radio.

Hammond rushed back to the diving bell to check on his dive partner, only to find him floating unconscious outside the diving bell. Hammond pulled Hoffman back into the bell, and after doing his best to resuscitate him, it was finally declared that Hoffman had died.

Both men were brought to the surface, and an investigation showed that Hoffman had died by drowning. It’s thought that he fell out of the diving bell with his mask off, inhaled water, and died.^[7]

3 Waage Drill II Accident

The Waage Drill II accident took place in 1975 when two divers named Robert Edwin and Peter Holmes were working in the North Sea off the coast of Scotland.

On this dive, the two divers headed down to 394 feet (120 meters) to do a short dive, untangling some rope along the rig. After completing the job, the two divers headed back to the diving bell to decompress.

As they were sealing off the bell, however, they noticed a gas leak. Despite their best efforts, they weren’t able to put a stop to the leak and were forced to move into a deeper chamber attached to the bell. This is where things really started to go awry.

Their supervisor, who was outside the chamber, began feeding helium into it to seal it off from the gas leak. However, because the gauge inside the chamber wasn’t working, he didn’t realize he’d overcompensated and sent too much helium into the chamber.

This caused the inside pressure to drop to a depth of 650 feet (200 meters) and the temperature to rise to a whopping 120°F (48.9°C). The two men inside the chamber were unable to breathe properly at this temperature and, after a few hours, died of hyperthermia.^[8]

2 Bibby Topaz Accident

The Bibby Topaz is a more recent diving accident that occurred in 2012. In this awful accident, a diver named Chris Lemmons was working on a subsea drilling structure with the support of a vessel named the Bibby Topaz.

However, while Chris was underwater, the Bibby Topaz’s positioning system malfunctioned, and it drifted 625 feet (190 meters) off course. The good news is that Chris managed to get out of the underwater structure safely, where he could await rescue. However, in the process, he snagged his umbilical support cord. This cord is what provided him with air, hot water, and communications.

That left the terrified diver trapped on the seafloor in total darkness. The good news is that back on the surface, the Bibby Topaz managed to regain their position and immediately realized what had happened. After just 40 minutes on the seafloor, they managed to pull Chris back to his diving bell and get him the medical help he needed. Chris thankfully survived the ordeal, and since then, the Bibby Topaz has made efforts to improve safety for its divers.^[9]

1 Johnson Sea Link Accident

The Johnson Sea Link accident took place in 1973. What happened is that a submersible named the Johnson Sea Link was sent down off the coast of Key West to help sink an artificial reef in the area.

There were two divers aboard the vessel, Edwin Link and Albert Stover, as well as the pilot of the submersible, who were meant to check out conditions on the reef below.

However, while under the water, the submersible got trapped in the wreckage of the very destroyer it was supposed to be monitoring.

Rescue efforts were launched immediately, and the submersible was eventually recovered. While the pilot of the ship made it to the surface alive, both divers had passed away due to carbon dioxide poisoning.^[10]

Cave diving is insane. That may be the shortest and most subjective opening sentence in history, but it is also supported by a mountain of evidence. A gruesome, water-logged, decaying, lightless mountain of evidence, scattered and wedged into thousands of cramped, jagged chambers beneath the Earth.

Combining the isolation and desolation of cave exploring with the powerlessness and (often literal) madness that can come with scuba diving, cave diving is quite obviously a tremendous challenge. Only the bravest and most skilled adventurers attempt this most extreme of extreme sports, and even then, their success is far from guaranteed.

The list gathers ten stories from cave divers who unfortunately found themselves in the creepiest of circumstances. Whether it’s close calls with death, brushes with the paranormal, or just plain tragedy, here are ten of the creepiest tales of cave diving.

Related: 10 Fascinating Cave Finds That Will Blow Your Mind

10 The Rescue

The Tham Luang rescue is likely the most famous cave rescue operation in history. Involving thousands of rescue workers, lasting 18 days, and drawing worldwide media attention, the story of one Thai children’s soccer team trapped in a flooded cave became a tense cultural phenomenon. However, the children were not alone in their crisis, and their would-be rescue divers suffered some of the worst injuries and trauma of the whole incident.

On June 23, 2018, twelve children and their young assistant coach began exploring the Tham Luang Nang Non cave system, and soon after, a sudden torrent of rain partially flooded the cave and trapped them inside. Starting the next day, international teams of rescue divers searched the newly-underwater cave for over two weeks.

All told, over 90 divers helped rescue the boys, and their mission was a success; all thirteen were rescued alive. However, two rescue divers died due to the operation—one during the dive and one a year later from a dive-related blood infection.

9 Rummu Prison

Luckily, the creepiness of Rummu Quarry doesn’t involve any death—at least, not directly. While on the surface, the site is a simple quarry and popular tourist destination, underneath its surface lies a sad, bleak history.

The quarry was formed when the limestone mine that forms its base fell into disrepair and began flooding. While it was still a mine, any limestone pulled from its rock walls came from the ceaseless, merciless hard labor of Soviet prisoners, specifically those sentenced to the Rummu prison work camp.

Though scenic at its surface, the quarry’s base still holds the remnants of the prison, including bunkers, walls, and rusting barbed wire to symbolize its cruelty.

8 Modesto Varischetti

Admittedly, the story of Italian miner Modesto Varischetti may be more peculiar than creepy. However, there is still plenty of creeps to be had when you consider what he went through.

In 1907, Varischetti was working in a gold mine in Bonnievale, Australia, when a severe thunderstorm quickly flooded major sections of the mine. He managed to find an air pocket during the deluge and sat there in the cold, silent darkness, awaiting rescue. 

Varischetti heard no sign of rescue for five long days when a rescuer in old-timey ocean-diving gear finally managed to reach him and bring him food. Even then, it took another four days for rescuers to extract Varischetti from the flooded mine.

As strange as it is, one of the miners who aided in Varischetti’s rescue was none other than future U.S. President Herbert Hoover.

7 A Missile Silo

Developed in 1959, the Titan I was the U.S.’s first intercontinental ballistic missile. The missiles were housed in underground complexes across the Western U.S., but by the late ’60s, the missiles’ obsolescence had rendered the complexes useless. 

The sites were gutted for scrap parts and largely left abandoned. After one site flooded, the silo near Royal City, WA, a private company gained permission to host dives through the site, and they are as creepy as they are majestic.

In one section, the tour company’s official synopsis of the dive reads, “You’d never know you were about to enter a 160-foot-tall chamber that housed a ballistic nuclear missile!” That should tell you all you need to know about the type of people who volunteer for this (manmade) cave dive. Divers can even find themselves “mere inches from where the massive Titan I ICBM which once stood at the ready,” which may creep you out for several reasons.

6 Ben’s Vortex

On August 18, 2010, Ben McDaniel disappeared after diving into Vortex Spring in Florida. After two dive shop employees saw McDaniel dive into the spring early in the evening, he was never seen again.

Though McDaniel’s disappearance could easily have been a simple, if tragic, case of diving error or misfortune, many are unconvinced. During the investigation, several odd pieces of evidence came to light, which led many to question the events of McDaniels’ last night—even suspecting foul play.

For a few examples, there is McDaniels’ odd behavior before his last dive; the recovered air tanks belonging to McDaniels that were found to be inconsistent with his dive plans; McDaniel’s own personal and financial troubles leading up to the disappearance; the suspicious death of the spring’s owner the following year; and the repeated police refusals to release important evidence to the case.

5 We Have to Go Back

Pluragrotta is a popular cave diving spot in Norway due to its beauty, extreme depth, and excellent underwater visibility. In 2014, it also became famous as the site of an awful diving accident, and subsequently, an amazing recovery mission.

In February, five Finnish divers attempted a long, deep dive through the caves. Only three were successful, and even they all experienced crippling decompression sickness. Divers were then banned from the cave, and an international team of rescuers searched the cave for the two bodies. After they deemed the mission too dangerous, the three original survivors took matters into their own hands.

With a large support crew but no official clearance, the survivors undertook a daring mission back into the cave’s depths to recover their friends’ bodies. They succeeded and alerted authorities of the bodies, prepared to accept their punishment for violating the cave ban. Instead, they faced no charges, with one of them even earning a medal from the Finnish president.

The documentary “Diving into the Unknown” chronicles the whole story, which is more dramatic and harrowing than any Hollywood blockbuster.

4 The Birth Canal

The story of the death of John Edward Jones has become notorious for its heartbreaking and protracted nature. It has even been referred to as “the worst death of all time.”

On November 24, 2009, Jones and his friends began spelunking in Nutty Putty Cave when Jones decided to attempt passage through a section known as the Birth Canal. The passage is frighteningly narrow and descends vertically, meaning Jones had to wiggle his way down it headfirst. Unfortunately, the mere act of breathing made Jones’s torso too wide for the passage, and he became stuck.

The details of rescuers’ attempts to free Jones are a grim slog of dashed hopes and slow suffering. At one point, Jones was even partially raised out of the Canal by a rope and pulley system, but the machine failed and plunged him right back to his original predicament. After more than 24 hours trapped upside down and compressed, Jones eventually lost his ability to breathe and died. Shortly before his death, rescuers managed to lower a radio down to Jones, who could speak to his wife one last time.

3 Mossdale

There’s no way to write a list like this and not include the 1967 Mossdale disaster. Located in Yorkshire Dales, England, the Mossdale Caverns were a popular hiking and cave exploration destination. We say were because the 1967 deaths of six cave explorers forced the local government to prohibit any future exploration.

The cave was a notoriously hard slog through varying terrain and water levels that led four of the original ten explorers to cut their adventure short, exiting the cave to safety. Sadly, the remaining six never joined their friends, as rapid rainfall flooded sections of the cave and prevented their escape. Rescue efforts over the next two days located the six bodies, confirming their deaths and cementing the Mossdale disaster as the deadliest cave incident in British history.

2 It Was All on Tape

The cave diving death of Dave Shaw is a multilayered tragedy. Warning: the attached video shows Shaw’s personal camera footage from the moments leading up to his death, and they are unpleasant.

The tragedy began with the 1994 death of Deon Dreyer. A decade later, while on a dive at the same site, Shaw found Dreyer’s missing body. In a class act, Shaw contacted Dreyer’s parents and promised them that he would return to the site and recover their son’s body for them. 

Shaw mounted the return dive as promised and reached Dreyer’s body again. Unfortunately, though, Shaw then began suffering from nitrogen narcosis, which prevented him from breathing and thinking normally.

Dave Shaw died next to the body of Deon Dreyer. The tragedy then continued as Shaw’s support diver, Don Shirley, nearly died trying to save Shaw as well.

1 The Iceberg Shifted

Jill Heinerth is somewhat of a legend in the cave diving community. She has filmed dive documentaries for multiple major channels, has authored an impressive library of dive-related books, and—as you would expect—has dived in a staggering amount of caves across the world. It should carry a great deal of weight to hear that she cited one diving trip in particular as containing several of the scariest moments in her life.

The trip Heinerth referred to was her dive into a newly-formed, moving iceberg. The object was, as she puts it, “an iceberg the size of Jamaica” that was “the largest moving object on our planet.”

Alongside two fellow divers/documentarians, Heinerth entered the submerged chambers of rock and ice inside the iceberg and saw sights that no human had ever seen before. They also almost died. Repeatedly. One of her peers almost froze to death; all three were trapped in a cave whose entrance had suddenly slammed shut. They were whipped around by currents, trapped in an unexpected chamber of ice, became slaves to another current, and became trapped again.

On top of that, the entire iceberg proved unstable. As Heinerth writes, “There was our iceberg—the cave that we had just been inside of, breaking into pieces, heaving up in the sea and sending these giant waves towards our boat. The whole square mile of ice we’d just been inside of was breaking apart and dissolving into the sea. I was just standing there, gobsmacked on the ship’s rail. I realized that if we had been in the water, we’d be dead.”