On April 6th, 1994, diving legend, Sheck Exley,
was attempting to break the diving depth record in the Zacatón sinkhole,
when something went horrifyingly wrong. This is his story. [intro music] Today's video is sponsored by Babbel,
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with the link in the description below. On June 29th, 1968, Sheck and Edward Exley pulled into the parking lot of one of their
favorite swimming spots. It was another of Florida's many hot summer days, and Wakulla Springs, located about
14 miles south of Tallahassee, was always a good place to get some relief. The Exley brothers weren't just your average
teenagers looking to cool off with a swim though. At only 19, Sheck was starting to become known
around dive shops in the area as a bit of a phenom. The local dive community even talked about him
like he was some sort of myth, with claims that he could extend the life
of an air tank longer than any human on Earth, or that he could leisurely descend to depths
that the average diver would pass out at. Hearing divers talk about Sheck was like listening
to a fisherman telling the story of his biggest catch, only each time he tells it, the fight gets
a little tougher and the fish gets a little bigger. And the two brothers trips to Wakulla Springs
probably played a bit of a role in building his reputation at such a young age. There are signs in the parking lot of Wakulla Springs
that warn that scuba diving is strictly prohibited. So this is where the brothers would come
to free dive instead and test their limits. During their swims, the brothers would take turns seeing
how deep they could get on a single breath hold before the need for air forced them
to rocket back to the surface. That day though, Sheck had a new piece
of equipment he was excited to test out. He bought a depth gauge that was worn on the wrist, and now these competitions with his brother
would have official measurements. After they eased into the warm water of Wakulla Springs, Sheck and Edward swam out to the deeper areas. One of them would then dive down
with the depth gauge and then return to the surface before
handing the gauge off to the other. Sheck always let Edward go first, and each time
his brother returned to the surface, Sheck would take the gauge
and go just a little bit deeper. When Edward logged 42 feet, Sheck came back
with a reading of 50 feet. But, determined to finally get the better
of his older brother, Edward took several deep, fast breaths before filling his lungs to capacity
and slipping under the water. At the surface, Sheck watched as Edward descended and knew immediately when he passed
his previous mark. Sheck estimated that Edward went further than
either of them had ever been without scuba gear, and Sheck was ready to congratulate him
when he broke the surface. But then when Edward turned to torpedo
himself back to the surface, Sheck watched as he suddenly went limp
and slowly dropped to the bottom. Sheck immediately descended to try to reach his brother, but Edward was unconscious, and he kept
falling deeper and deeper. So despite his best efforts, there was no way Sheck was going to be able
to reach him without scuba equipment. So instead, he swam as fast as he could
to the beach, hurried out of the water, and then ran to his car to grab
an air tank he had in his trunk. But then as he was doing this,
his body gave out on him. He collapsed from exhaustion after so many attempts
to reach Edward on a single breath hold. Thankfully, there was a fellow swimmer nearby who grabbed Sheck's dive gear
and entered the water to rescue him. The man descended and found Edward's limp body
on the bottom of Wakulla Springs, but there was still a chance he could be saved,
even if it was small. After the diver pulled Edward to the surface
and got him onto the beach, Sheck started CPR in front of a gathering crowd. By then, Edward had already been at the bottom
far longer than most could survive, but miraculously, Sheck managed
to get him breathing again. At that point, an ambulance was on scene
and rushed him to the nearest hospital, where he was placed on life support. Tragically though, he was taken off of it later that night when it became clear that he had no brain activity. This was beyond devastating for Sheck. And so from that moment, he dedicated his life
to establishing diving safety standards and protocols as a way to deal with his grief
and ensure that neither his parents nor the parents of any other diver would ever
have to suffer that kind of pain again. Over the next 26 years,
this pursuit became an obsession, as did a more specialized type of diving. The first time Sheck entered an underwater cave,
it was like love at first sight. At the time, it was a very new activity, and cave diving was without a whole lot
of training or safety standards. So from then on as well, Sheck became
one of the foremost experts in the community. So much so that he literally wrote
the book on cave diving. In 1979, he published his book,
Basic Cave Diving: A Blueprint for Survival, which is still considered the how-to manual for the sport. The book focuses primarily on safety and emergencies, but beyond the book, he also became
one of the most practiced, maybe even the most practiced cave divers ever. By 23, he had already logged more than 100 cave dives, and that number exploded to more than
4,000 by his mid 40s. But as much as Sheck loved adding to that total, it was extreme depth that brought out
the ultimate competitor in him. And luckily for him, he seemed to have some
rather unique abilities to withstand depth. The deeper a diver goes, the more risk grows. For starters, there's the crushing pressure
of water at depth. As a diver descends, the weight
of the water above increases. Go deep enough and the pressure of the water
will squeeze anything not built to withstand those forces like an empty water bottle. The dangers aren't just external though. Internally, depth has a variety of impacts
on the human body. If you're a regular viewer of the channel, you've likely
heard this explanation many times before, but bear with me because it's relevant
to Sheck's insane abilities. Conditions like nitrogen narcosis
and decompression sickness, or the bends, can set in fast and with little warning. As you go deeper, nitrogen in the bloodstream can build up too fast for the bodyto keep up with absorbing it. This then has a narcotic effect on the body
and can cause a person to feel intoxicated, hence the name nitrogen narcosis. It's often described as similar to being drunk,
with a lot of the same impairments. Severe nitrogen narcosis, though, can bring on
hallucinations, dizziness, and unconsciousness. All of which are obviously extremely hazardous
hundreds of feet in the water. To combat this, divers will use different
gas mixtures the deeper they go with less nitrogen than regular air. Weirdly though, Sheck seemed to be
almost immune to narcosis. While serving as a member of the support team for two divers trying to break the
air-only depth record in 1970, Sheck made it to 465 feet or 142 meters, before he experienced any effects of narcosis. Sadly, the two divers he was assisting
did not share that same resistance to narcosis and died during the attempt. Sheck was also the first person
to ever dive below 800 feet or 240 meters in technical scuba diving, which is a feat that has only been attempted
by 20 people in history as of 2021. And on top of his near immunity to narcosis, Sheck never once experienced a case
of decompression sickness. Decompression sickness, or the bends, occurs when all that nitrogen that was absorbed
into soft tissue on descent, floods its way back into the bloodstream
too quickly and creates bubbles. Most cases of the bends are not serious,
but it can cause death if it's severe enough. The best way to avoid this is by
making something known as a decompression stop during the ascent. The number and duration of these stops is
determined by how deep a diver goes and how long they stay at that depth, since these variables determine how much
nitrogen gets absorbed by the body. By stopping at specific depths and remaining there
for a set amount of time, the nitrogen is released slowly and doesn't form
large bubbles that can be a problem. As you might imagine, any diver with a resistance
to these conditions has a serious advantage. So by 1994, Sheck had all three of the
deepest dives of all time. A few years prior, Sheck had even
broken his own record by diving 881 feet or 269 meters. But he knew he could go further still;
he just needed somewhere to do it. It was around this time when his good friend
and diving partner, Jim Bowden, told him about a place he believed had
the deepest known sinkhole in the world. The cave that Jim was talking about is called Zacatón, and it's technically not a cave at all. It's a sinkhole called a cenote, which is a
cousin of the blue hole. Both blue holes and cenotes are created
as bedrock errodes and collapses over time to expose groundwater. The only difference between the two is that
blue holes are located near the ocean, and cenotes are found inland. They're often referred to as caves since that's what
they were before their ceilings fell in. When Sheck saw Zacatón for himself in 1993,
his enthusiasm exploded. The otherwise stoic and mild-mannered math teacher was like a kid the moment he resurfaced
from his first dive there. Almost right away, Sheck and Jim began
planning and preparing for a dive that would take them to 1,000 feet
or 305 meters and beyond. They spent the next year discussing
and examining every single little detail; everything had to be perfect. Calculations had to be made to determine
the type, blend, and the amount of gas the dive would require. Practice dive after practice dive
would also need to be done to ensure both men were not only
physically but mentally prepared to operate safely at a thousand feet or more. The result of their work was a solid
and specific plan. They got their support team set with divers,
Ann Kristovich and Marcus Gary, joining Sheck's wife, Mary Ellen, and Jim's wife, Karen. They wouldn't enter directly through Zacatón
since it was surrounded by tall rock faces on all sides. Instead, they would enter from a nearby spring and then swim through a 600-foot (183 m) tunnel
that connects the two. Before the dive, two weighted guide ropes
were set up in the cenote that both men would use to descend and ascend. When they were ready, Jim would descend first, and
Sheck would follow him after 10 seconds so they wouldn't collide since
they would be dropping fairly quickly. Unlike ascending, the descent could be executed
as quickly as a diver chooses, so they planned to drop to the bottom at a rate of
100 feet or 33 meters per minute. This meant the entire trip would take
about 10 to 12 minutes. Such a fast descent would help reduce the amount
of decompression time they'd need on the way up, since Sheck planned to just touch the bottom
and then immediately begin ascending. This is because at the depth they were aiming for, spending even one minute there, translated to hours
of additional decompression stops. During the descent as well, they'd need to switch tanks
and regulators on the fly once they reach specific depths. Incredibly, they planned to use six different
mixtures of nitrogen, oxygen, and helium across over 30 tanks. To avoid narcosis and make decompression as fast
as possible, this needed to be precise. But since no one had ever been to a thousand feet
or beyond, it was uncharted territory. Because of this, Sheck worked with a physiologist
to dial in the proper gas mixtures. And even though the plan called for Sheck to begin
ascent immediately the moment he touched bottom, and with tanks staggered along their guide ropes with gas mixtures intended to
shorten decompression stops, the return trip to the surface would still take about
10 hours and require 50 stops to complete. While they ascended, members of the support team
would descend to specific depths to wait for Sheck and Jim and assist as needed. Finally, after everything was planned to perfection,
they set a dive date of April 6th, 1994-- just six days after Sheck's 45th birthday. This was also when Sheck would be
on spring break from teaching. But throughout the year of planning, despite the
incredible physical shape he was in, Sheck spent a lot of time thinking about
his future in diving. He was another year older, and the invincibility
of his 20s and 30s was fading, which was something he found out abruptly. While diving a freshwater sinkhole in South Africa
called Bushman's Hole in 1993, Sheck had the first real underwater scare of his career. He was attempting to reach 863 feet or 263 meters when the helium in his tanks started to turn on him. This is because divers at extreme depths
are at risk of another condition. In addition to nitrogen narcosis,
they also have to worry about a condition called High-Pressure Nervous Syndrome
or HPNS. Like narcosis and decompression sickness,
HPNS is reversible but comes on suddenly with
potentially debilitating symptoms. It can set in anywhere below 500 feet
or 150 meters while breathing helium. The effects are also highly individual and based on variables
like how much helium is in a diver's mix, how deep they dive, and the rate of descent. During the 1960s, HPNS was first documented
by a US Navy physiologist who called the effects "helium tremors" since
violent shaking is one of the most common symptoms. HPNS can also cause extreme sleepiness,
changes in heart rate and rhythm, and decreased mental functioning. Sheck's descent into Bushman's Hole was also
performed at a rate of 100 feet per minute. And Sheck began to tremble around 700 feet
(213 m). Then his vision suddenly turned into countless tiny circles, each with black dots in the center,
and his skin became intensely itchy before transitioning into a stinging feeling. With all of that going on,
he continued his descent to 863 feet (263 m), at which point, his tremors were too bad to continue. He managed to begin his ascent
and stopped at 750 feet (229 m) to allow his body to adjust, but it was no use. The only thing that would averse his HPNS
was to keep going higher. Finally, he was able to get the symptoms to stop,
but the experience scared him. Even before then, he never viewed himself as immortal, and he was well aware of the potential dangers
that exist deep underwater. But those moments in Bushman's Hole
caused Sheck to start questioning whether it was time to step away from the
extreme depth record-chasing. It was something he had thought about
constantly since then, and when he came to a decision,
he announced to the diving community that his upcoming dive at Zacatón
would be his last extreme depth dive. Crossing the 1,000-foot or 305-meter threshold
was the perfect note to go out on. When April 6th arrived, Sheck, Jim,
and the support team made the drive to Zacatón
to make their final preparations. After learning about Sheck's world record attempt
and that it would be his last extreme dive, several sports publications and
a small TV news channel were on the scene to report on the attempt. When everything was ready to go,
Sheck and Jim entered the water and made it through the tunnel that
connected the spring to the sinkhole. As they surfaced inside Zacatón,
they couldn't help but notice the growing crowd of farmers and
locals on the surrounding cliffs. There's not a whole lot to see during
a cave dive for those on land, but people who live nearby weren't gonna miss
a world record attempt anyway. Sheck and Jim were appreciative of the interest
but didn't let the presence of the crowd distract them. As they bobbed up and down at the surface, both men
closed their eyes and started to meditate. They played the entire dive out in their mind's eye where they slowed their breathing
to just a few breaths per minute. Then, as if they could sense each other's readiness, they opened their eyes at the same time,
and Sheck nodded to his partner. At 9:45 am that morning, Jim disappeared
under the water with Sheck right behind him. On the descent, they were on compressed air
to 300 feet or 91 meters. At that point, they switched to a gas called HeliAir,
a term Sheck coined, which is just helium mixed with regular air. At 600 feet or 183 meters, they switched again,
this time to trimix, which is a combination of nitrogen, oxygen, and helium. If you're wondering how they were able to switch back
and forth between so many gases, it's because they were strapped with
200 pounds of gas tanks, which also conveniently helped their rapid descent. When Jim started to slow his descent
at the 750-foot mark, this is when the first problem began. Jim began involuntarily trembling. He didn't know it at the time, but his rate of descent
was much faster than planned, which meant he had been breathing too much helium
far deeper than he should have. As the trembling grew, Jim had no doubt
that HPNS was setting in, and it was only gonna get worse the deeper he went. But then when he looked over towards Sheck's rope, Jim saw she's light descending past him
toward the bottom. This meant that he had to keep descending. Then at 900 feet or 274 meters,
Jim checked his air gauges and was stunned by how much trimix
he had already consumed. There's always some variance with gas calculations, but they usually aren't big enough to impact
the dive or the diver. This was a pretty big discrepancy though. With one tank of trimix already finished, the
second tank was only showing 1000 PSI, meaning he was already about two-thirds
of the way through his supply. But even worse, if the pressure dropped below 500 PSI, gas would stop flowing through his regulator. He needed to ascend right away. So, at 925 feet, Jim inflated his buoyancy device
or BCD. Jim's wrist computer then set his first
decompression stop at 450 feet. By the time he reached that mark, the last of his
mix was gone, and so was his HeliAir supply. Fortunately, there was a tank of decompression
gas waiting there for him. As if things couldn't get any worse, when he
opened the valve on that tank, gas shot through the regulator, causing it
to fly out of his mouth. Thinking quickly, he switched the regulator connected
to the compressed air tanks on his back while he tried to fix the regulator as it flailed in the water
from the force of the gas leaving the tank. After messing with it for a while,
he just couldn't get the regulator fixed so he was left with only one option. He had to put the tank under his arm
and continue to ascend as he opened and closed the valve
when he needed to breathe. It was an agonizing process in an
already challenging environment. And making matters worse was that Jim
would need to make several decompression stops before he reached the next tank at 300 feet. When he finally got there, he ditched the tank
with the faulty regulator for a new tank with one that worked. Finally, he was able to breathe a sigh of relief
and turned his attention back towards Sheck. On the surface, the support team kept a close eye
on the bubbles rising from the water. About 2 minutes after Sheck and Jim
went under, the bubbles disappeared, which indicated they were beyond a ledge
that jutted out at around 250 feet. Based on the plan and the extensive calculations done, once the bubble stopped rising to the surface,
they should reappear within 12 to 18 minutes. And right on time, one set of bubbles broke
the surface above Jim's rope, but not Sheck's. Knowing that Sheck would be diving deeper than Jim,
the team expected to see Jim's bubbles first, and then a delay before bubbles
would reappear above Sheck's rope. But as time ticked by without any sign of Sheck,
the team grew concerned. One of the support divers, Ann, went back
to the spring, grabbed her tanks, and began making her way through the tunnel to
meet up with Jim and find out what was going on. Back in the water, on Jim's journey
from 250 feet to 170, he looked over at Sheck's rope and expected
to see it taut and moving, but it was just slack and still. He looked down and saw nothing but blackness;
there were no lights and no bubbles. Realizing what this might mean, he had
a brief moment of panic, but he managed to convince himself that Sheck
was just further behind than expected. When he reached his next decompression stop though, he saw Ann was waiting there for him,
and he could sense her worry. While they waited together for Jim's
decompression stop to end, they fixed their eyes on Sheck's rope,
just hoping to see any sign of life. On the cliffs surrounding the sinkhole, Sheck's wife, Mary Ellen, hadn't realized
anything was out of the ordinary until she noticed the others were gone. Then she walked to the spring where
she found Jim's wife, Karen, and the other support diver, Marcus,
looking distraught. Karen then approached Mary Ellen and gave her
the news that Sheck might be in trouble, but she was barely finished to the sentence before Mary Ellen was in the water and
on her way through the tunnel. When she made it to Ann and Jim,
she scrawled a message on her whiteboard, telling them that she was gonna go
look for Sheck at 250 feet. She then reached the ledge at that depth and expected to see Sheck's light
at the very least by that point, but there was nothing but the same
blackness below her that Jim saw. She dropped off the ledge and descended a bit further but without the right gas to continue,
she had to turn around. After Mary Ellen entered the water, Karen followed behind her and remained
at 100 feet to meet her. When Mary Ellen got back up to her,
Karen could see that she was in tears. Mary Ellen tried to continue ascending,
but Karen grabbed her wrist to see how far she descended while trying to find Sheck. She saw that Mary Ellen had to decompress
for 30 minutes before it was safe to surface. Karen then held Mary Ellen in her arms,
and they remained like that for the entire stop. On the banks of the spring, one of the photographers
noticed bubbles rising in the water and lifted his camera to his face. As he shot photos of Karen and Mary Ellen
surfacing and exiting the water, he noticed that they were both sobbing
when they pulled their masks off. He then put his camera back down as
Mary Ellen let out a scream of pure grief that would haunt anyone who heard it. Long after the others had returned to the surface, Jim was still in the midst of a decompression process
that still had hours remaining. During this, one of the support team divers met Jim
at his decompression stop around 60 feet and confirmed what Jim already knew;
Sheck was gone. To that point, Jim held on to the slim hope that Sheck
was just behind schedule and still working his way up. But with that confirmation, the hope was gone. Jim wanted to be anywhere other than being suspended
at decreasing depth for hours, but going to the surface before his decompression stops
were complete was dangerous. He had no choice but to remain underwater with his
own thoughts for as long as it would take. Finally, after almost 10 hours, Jim emerged
from the water alone. The shock among everyone surrounding Zacatón
became almost tangible as word spread. It was a scenario that was always a possibility, but no one really thought there would be
a dive that Sheck wouldn't return from. For a few days, no one even really knew what to do, but eventually, the support team and some locals
had to return to Zacatón to retrieve the equipment. When one of the team went to pull Sheck's rope up,
it was too heavy since there were still unused bottles
tied to it for Sheck's ascent. So as a team, they worked to pull up
more than a thousand feet of rope with a considerable amount of weight tied to it. Then as it broke to the surface, they realized
that at the end of it was Sheck's body. What exactly happened to Sheck that day
will never fully be known, but there are a couple of theories. Maybe the most likely is that Sheck
had another HPNS event. The physiologist who assisted Sheck theorized that
he likely didn't die as a direct result of HPNS, but if the tremors were violent enough, it's possible
that he lost his regulator and drowned. Another possibility is that despite Sheck's thoroughness, the gas mixtures could have just been wrong. Too much nitrogen can cause narcosis, too much
helium can fry the nervous system, and too much oxygen at too deep
a depth can become toxic. The consequences are just as dire
if any of the gases are too low as well. If anything was far off enough, it could have
caused any number of conditions with the potential to incapacitate him. How Sheck became tangled in the rope
wasn't clear either, but the way that he was attached to it
looked far more intentional than accidental. There's some speculation that Sheck
knew he was going to die and that he tied the rope to himself
so his body could be recovered without putting anyone else in danger. A week after being retrieved from Zacatón, Sheck was celebrated by his family, friends,
and the entire diving community that was grateful for the work he did
to make their shared passion safer. He was then buried next to his brother,
Edward, in Jacksonville, Florida. In a cruel twist given the circumstances,
when Jim left the water on that fateful day, he did so as the new world record holder for the
deepest dive on a self-contained breathing apparatus, beating the record Sheck both set and
was attempting to break when he died. Today, only five people on Earth have ever
been to a thousand feet underwater, but none would've accomplished the feat if not for Sheck
and his contributions to cave diving. The current depth record is 1,090 feet
or 332 meters set in 2014. Hello everyone, and welcome to Scary Interesting. If you made it this far, thank you so much for watching, and once again, a huge thank you
to Babbel for sponsoring this video. Make sure to check them out using the link
in the description for 60% off a subscription, and hopefully, I will see you in the next one.
