Tragedy at Extreme Depths: Sheck Exley’s Fatal Dive in Zacaton Sinkhole

Incident Location	Diver Full Name
Mexico, Zacaton Sinkhole	Sheck Exley

On April 6th, 1994, Sheck Exley, a cave diver and explorer, went into the Zacaton sinkhole in for a dive into the unknown at extreme depths.

Sheck Exley, an American citizen, was born on April 1st, 1949. He was just 16 years old when he decided to give diving a try in 1965. After making his first cave diving adventure in 1965, he gave cave diving his sole attention throughout his lifetime. Sheck’s passion for cave diving drove him to find a paying job that would help him finance his diving career.

Prominence in Cave Diving

Just eight years after he started his diving career, during springtime in 1973, Sheck joined the 8-day mission to the Hydrolab underwater habitat in the Bahamas, where he worked as an aquanaut. Sheck continued with his passion for diving and exploration of caves until he became prominent in this field.

Contributions to Cave Diving

Sheck was an exceptional diver with a heart of gold. Part of his commitment to diving was shown when he started publishing books on the subject of cave diving. He authored two outstanding books for the community of divers: “Basic Cave Diving: A Blueprint for Survival” and “Caverns Measureless to Man.” Sheck also became one of the Chairmen of the American Speleological Society, specifically the Cave Diving Section.

Safety Innovations

Sheck saw the need for safety rules and procedures to be put in place during dives, and he contributed significantly to the development of such protocols. One of the procedures he introduced was “The Octopus,” a diving regulator used as a backup in case of a failure during a dive. The Octopus has become a major piece of equipment in scuba diving, both in cave and open water diving. Sheck’s contributions have made a lasting impact on diving safety.

Diving Achievements

Sheck was known for meticulously planning his dives. He was the first technical scuba diver to dive below 800 ft (240 m) and had a remarkable record of more than 4,000 dives without experiencing decompression sickness. He also had great narcosis resistance, which is uncommon among divers. Sheck’s experience and expertise made him a respected figure in the diving community.

The Dive into Zacaton Sinkhole

On April 6th, 1994, Sheck Exley embarked on an adventure called the “El Protector de Buceo Profundo” project at the Zacaton sinkhole in Mexico. Together with his diving buddy Jim Bowden, they entered the sinkhole, which has a depth of about 1,112 ft (339 m), making it one of the deepest sinkholes in Mexico.

He always planned his dives carefully. The multistage decompression used for these dives in open water most of the time takes about 13 hours and 30 minutes. Despite all this, Sheck never experienced any classic cases of decompression sickness in his diving adventures.

Besides, Sheck had great narcosis resistance; he wasn’t easily affected by it. It’s an unusual thing, though! Very few divers have been able to survive the depth of 400 ft (120 m) in an open water dive. Sheck was one of those few. On the 6th of April, 1994, Sheck Exley went into the Zacaton sinkhole in Mexico. At that time, Sheck had acquired 29 years of cave diving experience and had made more than 4,000 dives.

Sheck left for an adventure called “El Protector de Buceo Profundo” project at Zacaton sinkhole, together with a diving buddy, Jim Bowden. This sinkhole has a depth of about 1,112 ft (339 m), which ranks it as one of the deepest sinkholes in Mexico.

The depth of this sinkhole was measured with the aid of an autonomous robot. Sheck and Jim set out into the sinkhole independently, but they were using the same techniques. They decided to use independent dive descent lines to prevent being in contact with potential interference during the very fast descent. Each of their dives would be conducted separately, but the maximum depth of this dive was unknown.

So, they started a new dive line and swam along a 600 ft (183 m) passageway to the sinkhole. As they completed their equipment check, they agreed that they were finally ready, and they signaled this with a nod to themselves. At this point, they got separated to follow their respective descent lines through the water body.

Jim dived for a few seconds before Sheck joined him. They were about 25-30 ft (8-9 m) separated from each other, but they were connected with the guidelines, visually keeping track of these guidelines. They had to be careful in their descent because any mistake while diving down could lead to a catastrophic incident.

After they had descended for a while, Jim looked over to Sheck, who in turn nodded in affirmation. This prompted Jim to submerge, and he paused for a minute at about 10 ft (3 m) before going for a free fall. While diving, Jim and Sheck needed to follow a careful breathing pattern; they took conscious, slow, deep breaths so that they could optimize the trade-off between excess gas consumption and hypoventilation. These excesses can lead to carbon dioxide buildup.

While diving in this kind of condition, you must be very careful because any alteration in the pattern of your breathing, especially if it is a change in the rate of breathing, will alter the calculation of air you previously made. Both divers planned their descent to be 10 to 12 minutes.

Descent and Gas Management

But for the sake of decompression and to be able to optimally manage gas, it is preferable to take a rapid descent. Jim had planned a descent rate of 100 ft (30 m) per minute to 300 ft (91 m), then to 600 ft (183 m). However, when his descent got to around 750 to 800 ft (229 to 243 m), he planned on slowing down because this is the depth he had previously experienced High-Pressure Nervous Syndrome when diving in the Bushman’s hole (South Africa).

Both Jim and Sheck were breathing from their air cylinders till they reached a depth of 290 ft (92 m). Upon reaching this depth, Sheck waited a moment to stage his air cylinder. He fixed the cylinder to the line at 290 ft (92 m). Jim, on the other hand, made use of a small pony cylinder as his back-mounted cylinder for his air supply. Both of them later switched to Trimix (10.5% oxygen and 50% helium, and the rest was nitrogen). This trimix is a travel mix used mainly for deep depth dives because they were proceeding from a depth of 290 to 580 ft (89-179 m). Both of them had well-planned gas mixes for a safe dive.

The Encounter at 800 ft

The dive was going according to plan, but as Jim crossed the 800 ft (244 m) mark, he saw a light shining in front of him. He could see Sheck’s light far away. In the meantime, Sheck continued into the distance, and he was going at a faster rate than before. Usually, this rate of descent is so fast that it could lead to High-Pressure Nervous Syndrome. At 700 ft (213 m), his body couldn’t take it anymore and it started going into fits. His vision was obstructed by hundreds of small concentric circles with sparkling dots, and he started experiencing itching and stinging all over his body.

This was High-Pressure Nervous Syndrome brought about by several rapid compressions. The extreme pressure of his descent has affected his brain function, and this caused his neural circuits to run wild. At 750 ft (229 m), Sheck stopped considering his options, which was to abort the descent or continue further down. He decided to continue his descent, but at a slower rate.

Exploring the Unknown Depths

When the bottom of the cave bottomed out at around 860 ft (250 m), Sheck’s body started shaking uncontrollably, but he ignored it. But, even without seeing clearly due to the High-Pressure Nervous Syndrome effect, he noticed he was on a lunar landscape, which was covered with small rocks and covered with nearly 1 ft (0.3 m) of black sediment. He had gone deep into the water where no one had ever been.

He couldn’t stay down there for a long period because he would have to decompress for a longer time if he did, which would last for extra hours. So, he inflated his buoyancy device and started rising, and when he was halfway there, till he got to the surface, the syndrome subsided. Meanwhile, Jim was at 900 ft (274 m) before he was shocked when he realized that he had used more air than he planned.

Challenges and Tragedy

Going at this rate, he could encounter a failure from his regulator, which would be a huge issue for him. So, he inflated his buoyancy control device which halted his descent at 920 ft (280 m) and switched from his main tank to his backup tank at 450 ft (137 m). Now both of his air tanks were empty, so he had to make use of the staged air he left while he was on the descent.

This is usually done by divers when descending so that they can use it while coming up to the water surface. However, something horrible happened to him. When he turned on his new air tank, the regulator broke off with force. He panicked! He managed to reattach the regulator, but his mind was not at rest because it was no longer secured. He had to open and close the valve with each breath.

He had around 8 minutes of stops between 350 ft (106 m) till he got to where the next stage bottle was. Then he switched to the staged air with a functioning regulator and breathed a sigh of relief. At 250 ft (76 m), Jim switched to another air tank. At this point, he noticed that something was wrong with Sheck. He saw that the line Sheck used for his descent and his stage bottles were unused.

Discovery and Grief

His heart sank, but he consoled himself with the fact that Sheck had gone far below and would resurface soon. While consoling himself, he also questioned why Sheck would dive so deep into such a dangerous sinkhole. So he began to dive upward for decompression which would take up to nine hours. Kristovich, who was their support diver, was on the surface of the water watching the bubbles coming from the two divers.

About 18 minutes into the dive, Kristovich discovered that it was the bubbles coming from Jim alone. She could see that Sheck’s bubbles had stopped. As a result of this, she exchanged glances with Jim’s wife, Karen, and she dived to meet him at the 47-minute mark. She was relieved to see him but was shocked when she saw Sheck’s equipment still untouched.

However, Mary Ellen (Sheck’s wife) was watching from the cliff with no idea of the grave situation that had happened. Mary went to meet Jim’s wife, Karen, and they assessed the situation. Then she took an extra stage bottle and dived to meet her husband. She met with Jim and Kristovich, and her fears were becoming a reality.

Heartbreaking Loss

She quickly wrote on a dive slate that she was diving to 250 ft (75 m) in search of her husband’s bubbles, thinking that a ledge could have obstructed them from seeing the bubbles, but sadly, there were no bubbles when she got there. Jim’s wife had also worn her gear and caught up with Mary at 150 ft (30 m) as she was coming back up. She was crying, and her mask was messed up.

But Jim took hold of her gauge and saw that it read 278 ft (85 m). He had to hold her down for decompression for more than 40 minutes. That period was a very sad and lonely period for them. Jim later learned that Sheck was lost when he got to the 60 ft (20 m) stop. The remaining decompression period was a long and painful period for him. He never thought Sheck wouldn’t make it out alive.

The Tragic Outcome

At the age of 45, Sheck breathed his last breath during an adventure into one of the world’s deepest sinkholes; the Zacaton Sinkhole. This dive made Jim the first successful diver to break the 900 ft (274 m) barrier on the self-contained scuba air. His record depth of 925 ft (280 m) overshadowed Sheck’s old 881 ft (271 m) record.

Jim returned to the surface with pain in his shoulder and was immediately treated with oxygen, corticosteroids, and hydration. On the 7th of April, 1994, Kristovich and other support divers who were at the surface during the dive, all went back to the sinkhole to recover equipment from both guidelines. They discovered that Sheck’s equipment was very heavy, together with the steel tanks.

The recovery team decided to use a pulley from the surface to draw out that equipment. After two days, during the process of recovery, the body of Sheck came to the surface. When his body came to the surface, the lines were found tied around his arms together with the valve of the mounted bottles at his side.

Though the back-mounted bottles, valves, mounting plate, and his Buoyancy Compensator (BC) were not wrapped up together. His mask and other diving equipment were in place, but his regulator wasn’t in his mouth. His BC was intact, having gas in it, and his inflator was still working. The wrist-mounted dive computer showed a maximum depth of 904 ft (274 m), which means the travails that led to his death started nine minutes into the dive.

When the gases in his cylinder were analyzed, it showed that he had an accurate mix. When the autopsy was conducted, there was nothing that could be explained as the cause of the accident. This could have been a result of the effect of immediate decompression and the fact that it was the third day that they were trying to conduct the postmortem analysis. They had difficulties with confidently making a postmortem analysis of Sheck’s body.

Before your next dive, consider insurance – it’s like having a dive buddy for unexpected challenges. Dive safe, dive covered. Explore options here

FAQ