Risky Thailand cave rescue relied on talent, luck—and on sticking to the rules

By Chris Peterman

Last week, the world was riveted by the successful rescue of a youth soccer team as they and their coach were pulled out of a flooded cave in Thailand. The team had been stranded on a narrow rock shelf in the dark for two weeks, the way out blocked by turbid stormwater. The rescue involved far more than a few divers putting on gear and heading into the cave—it required a tremendous amount of technical skill and posed extreme danger.

But why, exactly, was it so dangerous? And what would it feel like to dive in those kinds of conditions?

I’m a professional diver with 16 years of dive experience, including safety diving and cave diving, and I have trained numerous scuba instructors. I also work full-time in a safety diving role, so answering the first question from a technical perspective is easy enough. The short answer is that all cave diving is dangerous (we'll dig into why below).

But to answer the second question, I decided to open my logbook and go back to a dive from many years ago—well before I was diving professionally. As a few select passages below highlight, this was a dive where things almost went fatally wrong.

The author during a much later (post-certification!) cave dive, with properly rigged cave diving gear.
Enlarge / The author during a much later (post-certification!) cave dive, with properly rigged cave diving gear.

Into the dark

My first experiences in cave diving were incredible. Once I slid under the surface and into a cave, I entered an alien world filled with incredible rock formations, strange sounds, and a darkness so complete as to defy imagination. My dive buddy and I had made several scuba dives in fully flooded caves and were truly enjoying our new-found sport. There was just one problem: while we were both experienced divers, with hundreds of logged dives under our belts, neither of us was actually certified to dive in a cave. And in a cave, things can go wrong—quickly.

Cave diving has five rules. These sum up the hard-won wisdom of the cave-diving community, as conducted through the analysis of cave-diving accidents and fatalities. Though the exact wording of each will differ from instructor to instructor, the rules are:

  • Be well-trained and do not dive beyond your certification level
  • Never use more than one third of your breathing gas to enter the cave—reserve one third for exiting and one third for emergencies
  • Maintain a physical guideline back to the cave entrance at all times
  • Never dive below the appropriate depth for your breathing gas mixture
  • Carry at least three lights per person—one main and two back-ups

Since these rules were introduced in the late 1970s (first as only three rules, later expanding to five), fatalities per number of dives have dropped among the cave-diving community. Today, the largest segment of fatalities in underwater caves comes not from certified cave divers but from divers not specifically trained by a professional cave instructor to be in that environment.

The first of these rules is therefore simple, and one that I broke badly: never dive beyond your certification level.

This rule alone would have made the rescue a challenge. The boys trapped in the Thai cave had no diving—and in some cases no swimming—experience when they had to dive into the waters blocking their passage to the surface of their dark prison. Their first experience underwater in a cave was probably terrifying, with very low visibility, buffeting from high rates of water flow, strange booming and rumbling sounds from their expelled breathing gas moving across the ceiling, and the glowing orbs of their rescuers' lights.

Get in line

On one dive soon after starting to cave dive, we were 100 feet (about 30 meters) into the cave and about 100 feet underwater—well beyond where natural light penetrated in that particular cave but not terribly far from the entrance. Suddenly, I noticed my buddy’s light beginning to move erratically. I was on one side of a restriction, a part of the cave that narrows such that only one diver can fit through at a time; my buddy was on the other side. I turned around and poked my head through to see what was going on.

One of the major technical challenges in the Thai cave was to get the boys through a 15-inch-wide (about 38cm) restriction in the cave that exited the water on an incline. The rescue divers reportedly stationed themselves in front of and behind each boy during the underwater portion of the rescue, which is standard practice in an emergency situation. Unfortunately, due to the small size of the restriction, the divers had to remove their tanks and push them ahead or drag them behind while also tending the victim and the victim’s scuba tank.

A narrow area in a karstic limestone cave similar to the one in Thailand. If you look at that and think "I want to go to there!" then you might be a cave diver.
Enlarge / A narrow area in a karstic limestone cave similar to the one in Thailand. If you look at that and think "I want to go to there!" then you might be a cave diver.

This would have been extremely claustrophobic for all involved (seriously—grab a tape measure, reel it out to 15 inches, and imagine squeezing yourself through an irregular hole about that wide at its widest point). For a while, all the boys would be able to see would be rock right in front of their faces while feeling rock scraping along their bodies on all sides. During their time in the restriction, the rescue divers would also lose some ability to check on the victim.

Breathe in, breathe out

After poking my head out of the restriction, I saw my buddy signaling that he was out of breathing gas. In that instant, the cave turned from a fun place to seek new things into a claustrophobic and confusing labyrinth. I rushed to my buddy and found that he had already switched to a tiny tank of breathing gas used for such emergencies (a so-called “pony bottle”). But the pony bottle, too, was reading low—we had forgotten to fill it before starting our dive. We spent a few moments assuring each other that everything was OK, then decided to return to the cave entrance. It was then that I noticed I was running low on air as well.

Another rule of cave diving is to use only one-third of your entire gas supply on the way into a cave—leaving another third to exit and the final third for handling emergencies. Unsurprisingly, this is called “The Rule of Thirds.” This approach also leaves enough gas to help a diver who has experienced an equipment failure breathe off a dive buddy’s gas tanks, making it back to the cave entrance even from the furthest point in the dive.

In Thailand, one of the first things needed after the soccer team was discovered was to deal with the logistics of supporting all of the dives required to effect a rescue. This would mean having support divers cache breathing gas tanks ahead of the main rescue divers so they would have enough breathing gas to make it to the boys’ perch in the cave and back out. Every time a dive was completed, the support divers would have to clear the used tanks and place new ones for the next set of dives, dragging tanks in and out of the cave repeatedly. Even these support dives were fraught with danger, as evidenced by the loss of one of the support divers who ran out of breathing gas on his way out of the cave after placing tanks for the main rescue divers.

Page 2

Lights from a dive partner during a cave dive. Even nearby light sources can be disorienting.
Enlarge / Lights from a dive partner during a cave dive. Even nearby light sources can be disorienting.

My buddy and I started toward the exit but realized that our scuba gear configurations were hampering us by not being “clean”—that is, not tightly packed against our bodies. We were also using handheld flashlights, which kept half of our hands from dealing with other problems. Dealing with the configuration of our gear stole precious seconds from time we needed to get out of the cave. On top of it all, my buddy had a leak in his drysuit (a type of suit worn over dry clothing in diving to keep the diver warm). This caused cold water to enter the suit, robbing him of body heat and adding to an already stressful situation.

Lights are also covered by the rules of cave diving. While the actual rule says to have at least three sources of light at all times, the basic principle can be extended to all cave-diving gear. One must have appropriate and redundant equipment, including breathing gas tanks, lights, scuba regulators, and anything else necessary to stay alive under a ceiling of rock with no way out but the path you came in on.

The Thai soccer team would have been chilled even before entering the water to escape the cave. Once in the water, even with wetsuits, the boys would have been downright cold. The water likely was in the low 70 degrees Fahrenheit range (or low 20s in Celsius), which can cause uncontrollable shivering within 30 minutes for someone without thermal protection. Adding to the stress of the cold was the fact that the boys were using non-standard cave-diving gear in the form of full face masks, which would make their own breathing sound vaguely Darth Vader-esque.

They also used a single breathing gas tank instead of the usual two, reducing the margin of error and violating the redundancy rule—though the decision to shave that margin likely contributed to a successful rescue in the end. Single tanks are used in cave diving, usually for "stage tanks," to increase the range of a cave-diving team or as part of a cave-diving gear configuration called "sidemount diving." But it's fairly rare for a single tank to be used alone as a primary breathing gas source. The main reasons for this are that it reduces safety margins by introducing single points of failure at the tank valve and scuba regulator—one failure and the entire system becomes compromised. Plus, a single tank simply holds less breathing gas than double tanks.

Hansel and Gretel

We had been diving in the cave with no guideline to lead us back to the surface. We had memorized the layout of the cave while diving and had used those memories to find our way around, since there wasn’t a map available for this cave. At the time, we thought this was enough to ensure our safety. We headed back toward the expected entrance, only to find a solid wall of rock. We looked to our sides and saw only more rock. Behind us was the tunnel we had just come through, leading deeper into the cave. For the first time in my diving life, I was truly scared underwater. The primal part of my brain started to scream that this was a good time to start panicking.

The five rules address my "I'm lost and I think I'm going to die in this cave" situation as well. When diving in caves, it is imperative to have a continuous physical guideline that extends from where you are to a spot outside the entrance to the cave. These strings and ropes (known as "cave lines") can be permanently installed, carried by the divers, or a combination of the two. Customized markers called "arrows" and "cookies" are used to mark lines so divers can find their way to safety using touch alone. The use of cave lines is drilled over and over again into students during cave training.

Another shot from a dive in a karstic limestone cave, similar to the one in Thailand. Visual navigation is difficult and confusing—physical guidelines are mandatory.
Enlarge / Another shot from a dive in a karstic limestone cave, similar to the one in Thailand. Visual navigation is difficult and confusing—physical guidelines are mandatory.

The two British cave divers who were initially sent into the flooded sections of the Thai cave to find the boys were trailing cave line. This line would have served as a literal lifeline, not only to the divers but also to the soccer players after they were found. It would also allow for medical personnel and supplies to traverse the cave in murky water with very low visibility. However, if a diver were to lose the line, the situtation could quickly become fatal. For the boys, this line would have been the only thing they could put their hands on to reassure themselves that they were indeed headed to the surface during the rescue.

Whether from losing the line, getting water in their masks, or letting their imaginations create monsters in the murky water, panic would have been the greatest enemy to both victims and rescuers. I've dealt with panicking divers many times, and their only thought is to fight anything that they consider a threat, even if that "threat" is someone helping them. Many diving fatalities come about because victims cause their own death—and that of would-be rescuers—through blind panic.

For the boys, who were being subjected to an alien environment with the sound of their exhaled gas booming and rumbling along the ceiling and their rescuers only visible as flashing blobs of light, panic could easily have overwhelmed them. This explains why, as the BBC reported, "The Thai government says the boys and the coach were given anti-anxiety medication to relax—but several sources have told the BBC that they were in fact heavily sedated, and only semi-conscious during the journey—to ensure they would not panic."

Into the light

After what felt like an eternity, we caught the very pale glow of natural light above us. However, in this cave there was also what’s known as a "false chimney"—a place large enough for light to enter but too small for a person to get through. I knew that at least one other diver had died trying to get to the surface by following this cave's false chimney. I had no idea where it was in the cave, however, or if that was what we were seeing. With both of our gas supplies running low, we headed toward the light. As we swam up, we saw that the light was stronger but also seemed to be coming from the side, which added confusion and doubt. Suddenly we saw the most wonderful thing we could imagine: the glow of natural light through the entrance. The total time from the first “out of air” signal until surfacing was less than 10 minutes—but it felt like (and could have easily become) an eternity.

The situation I was in so many years ago happened quickly and was over in a matter of minutes. Even so, it completely changed the way I dive and helped push me into my current career.

For the boys on the soccer team, it took five hours to exit the cave, with at least two of those hours spent in the water. I cannot imagine the levels of stress imposed on both the boys and their rescuers during this time. The divers had to balance the safety embodied by the rules of cave diving with the practical necessities required by this unique operation, and I am truly amazed at the success of the rescue. It took nearly 100 divers working alongside thousands of other rescue personnel to run lines into the cave, to get tanks filled, checked, and staged at forward locations and to make sure that all the necessary equipment was set up and ready to go for the main rescue divers. It took divers going into less-than-optimal conditions following that one guideline in the darkness to bring everyone out.

The cave itself seemed to make a point as the rescue was ending—right after the main rescue and soccer teams were safely out, the pumps keeping the water at bay began to fail and the rising water level chased the support divers as they raced to remove the tanks they had painstakingly kept ready for the rescue team. Had the rescuers made any decisions other than the ones they did, the story would not have had such a successful outcome.

Chris Peterman is a Scuba Instructor Trainer, Full Cave Diver, and Safety Diver. He moved from working in IT full time to working full time in a safety diver role six years ago. He lives in Houston with his wife and daughter and still gets the chance to "fun dive" and teach scuba classes outside of work from time to time.