Thai rescue teams arrange water pumping system at the entrance to a flooded cave complex where 12 boys and their soccer coach were trapped since June 23 in Mae Sai, Chiang Rai province, northern Thailand. Photo courtesy of Royal Thai Navy

Like most of the world, I watched with hope and fascination as selfless Thai military divers and expert volunteer cave divers from around the world saved 12 boys and their soccer coach from certain horrific death 2.5 miles inside a flooded Thailand cave. The Daily Report’s Jonathan Ringel asked me, an avid cave diver, if I’d offer some observations on the rescue. 

First, this rescue was every bit as sensational and miraculous as the media have portrayed it. The Tham Luang cave passage that trapped these boys when it flooded comprised nearly two miles of dry cave interrupted by several underwater passages, or “sumps.” The rescuers had to dive through each of these, including with children who can’t swim.

Most of my cave diving experience has been in northern Florida, which boasts some of the most challenging cave diving in the world. Under the best of circumstances, cave diving poses significant risks far beyond recreational scuba diving, including light failure, lost guideline, disorientation, drysuit failure (wetsuits are rarely suitable for cave diving because of the cold water and long durations), hypothermia and loss of breathing gas. To these dangers, present in every submerged cave, the Tham Luang rescue added far more.

Restriction

To reach and extract the boys, divers had to squeeze though a narrow passage, or “restriction.” Many caves have restrictions. But few cave divers will attempt a restriction so narrow that it requires a diver to completely remove his or her breathing gas tanks and push them through with hoses trailing behind, as the rescuers had to do with boys’ air supply. (Some cave divers “sidemount” their tanks under their arms to reduce bulk on their backs to access cave passages designated “sidemount only.”)

Variable Water Flow

The flow in some caves, like Twin Cave in Jackson County, Florida, is relatively low. In others, like the cave under Weeki Wachee Springs (of mermaid show fame), the flow is so strong that authorities closed it to nearly all cave diving in 2001. Because of seasonal monsoon rains, Tham Luang’s flow varies treacherously between these two extremes.

Horizontal Penetration

The rescuers’ challenge was not the depth of the water; a recreational scuba diver on holiday in the Caribbean would routinely dive to depths greater than this cave’s. But a recreational diver can surface at any time, making an out-of-air death extremely unlikely as long as the diver follows his or her training. In the underwater portion of the Tham Luang rescue, the divers were over half a mile from the normally oxygenated air on the exit side of the sump, and then as much as two miles from ambient light in the dry sections. By comparison, many highly experienced cave divers have never ventured more than a half-mile from a cave entrance.

Visibility

In Florida caves, the water is usually gin-clear. That is, unless a careless diver stirs up silt, which can instantly reduce the visibility to roughly that of chocolate milk. In Tham Luang, however, the sudden and variable flow of rainwater could plunge the visibility of the entire underwater passage to zero through no fault of the divers. In these blackout conditions, the rescuers had to maintain constant physical contact with their guideline and exit the half-mile sump entirely by feel, all while also holding the boy they were rescuing.  

The greatest risk to these boys—who don’t know how to swim, let alone engage in the most dangerous form of scuba diving—was panic during their underwater extraction. Cave divers’ training and years of experience reduce the risk of panic in these hostile environments. A panicked diver in any environment is a great risk to himself and his rescuer. A panicked diver will frequently spit out his mouthpiece and tear out his rescuer’s. In a cave, panic almost always equals drowning.

Robert Highsmith.

Aware of this risk, the rescuers wisely used full-face masks on the boys. Unlike traditional gear that requires a diver to hold a breathing gas regulator in his or her mouth and keep a dive mask with a single strap on his or her face, full-face masks securely seal the wearer’s face from forehead to chin. They are much harder to dislodge, can enable voice communication among divers, and will continue to supply respirable gas even to an unconscious or thrashing diver. The Georgia Aquarium volunteer dive team, on which I served for four years, uses full-face masks for certain maintenance operations because of this additional margin of safety.  

As a final observation, most media have repeatedly referred to the divers’ “oxygen tanks.” It would greatly surprise me to learn that any of these rescue dives used pure oxygen. For cave dives in water depths less than 100 feet, plain old compressed air—which is only 21 percent oxygen—is usually the breathing gas of choice.  

In sum, these rescuers, most of whom were volunteers with a life-long passion for an extremely challenging but rewarding activity, subjected themselves to cave conditions far, far more dangerous than they would have normally chosen in order to save these 13 lives. Indeed, a retired Thai military diver sacrificed his life while staging additional breathing gas along the underwater exit route. We owe them all a great debt.

Robert Highsmith, a partner in Holland & Knight, is certified by the International Association of Nitrox and Technical Divers to dive to depths of 330 feet using helium-based hypoxic breathing gas, and full-cave certified in the use of the Inspiration Vision closed-circuit rebreather by Technical Diving International.