Thai soldiers lay electric cables deep into the Tham Luang cave on June 26 during the initial rescue effort to locate the missing children’s football team and their coach LILLIAN SUWANRUMPHA/AFP/Getty Images

Thana Slanvetpan usually spends his days inspecting oil wells and gas pipelines. But when a call for help came in from rescuers searching for a football team of 12 boys and a coach lost in a cave in Northern Thailand, he sprang into action.

Slanvetpan is a senior engineer at PTT Exploration and Production (PTTEP), and one of hundreds of people from all over the world who travelled to the Tham Luang cave complex during the nine-day search, offering assistance, prayers, or technology.


On Monday, two British divers reached the team, but the challenge is far from over. Technology – both old and new – helped find Thailand’s lost boys, and now it could be crucial in getting them out safely.

The dangers involved in rescuing the group were put into sharp relief on Friday, July 6 when Petty Officer Saman Gunan lost consciousness on his way out of the Tham Luang cave complex, where he had been delivering air tanks. Gunan, 38, and formerly of the Thai navy, ran out of oxygen on his dive back to the surface and could not be revived. For the dozens of people involved in the ongoing rescue mission, conditions aren’t likely to get any easier.

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Drones and robots

“We didn’t know what the conditions at the site would be like,” says Slanvetpan, who has been leading a 30-strong team of PTTEP engineers assisting in the search on-site. “So we tried to bring all the technology that we thought could be useful.”

This included three aerial drones, equipped with 30x optical zoom lenses, and thermal cameras. These are routinely used for carrying out high-risk inspections of potential drilling sites, but found a new role during the search – first in creating a 3D aerial map of the area, and then in spotting potential access points into the cave from above.


Multipurpose plant inspection octocopters, or MPIO, have been deployed to search for potential access points into the cave from above PTTEP

“The benefit of the drone is that it simplifies the search,” says Slanvetpan. “They probably have 100 potential access channels into the cave. Instead of having the ground force climb up and check every location, you just need the drone.”

PTTEP also brought two underwater vehicles – one remotely operated by a human, and the other a prototype for an autonomous underwater drone that is currently in the research stage. They are equipped with sonar scanners that can create an underwater map of the cave, which could be useful to the divers working in muddy waters with very poor visibility.

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However, after consulting with the SEAL team that has been exploring the cave complex, it was decided that the situation was too challenging for these vehicles to be deployed. “The terrain is much more difficult than what we’ve tested it on before,” says Slanvetpan.


Dark water and obstacles

Perhaps the biggest problem posed by cave rescues is communication. “Regular radio devices fail in this complex environment of dark water and obstacles,” says Uzi Hanuni, CEO of telecoms equipment supplier Maxtech Networks.

To help, the Israeli company flew one of its engineers out to Thailand last Monday, along with 17 radios equipped with mesh technology. These devices, built in the UK by Entel, have software developed by Maxtech that enables them to broadcast and be used as a relay simultaneously. This means that they can communicate over a range of up to two miles, without direct line of sight, or the need for any physical infrastructure such as radio towers to bounce signals off.

Rescue workers inspect pumping machines at the entrance of Tham Luang Nang Non cave on July 2 Linh Pham/Getty Images

The virtual networks are designed for first responders in the aftermath of a natural disaster, or firefighters battling flames in remote forests, but they found a use here in the mountainous terrain.

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“It’s automatic and highly dynamic,” says Hanuni. “You don’t need to pre-program the radios, you just go inside with them, wherever you want and they work automatically.”

Meanwhile, the British diving team who made first contact with the trapped party turned to a much older technology to get messages to the surface.

HeyPhones were developed almost 20 years ago by and for the British caving community. They are bulky, do-it-yourself radio systems that use ultra-low frequency waves to communicate through hundreds of metres of solid rock.

Volunteers from the Derbyshire Cave Rescue Organisation spent last Tuesday testing and packing three of the devices, which were sped to Heathrow under police escort and then flown to Thailand to be used in the search.

Now that the boys have been found, the Thai authorities have been working on establishing a more robust line of communication. Throughout Wednesday, divers were attempting to thread a fibre-optic cable through the cave’s narrow chambers to enable direct contact with the surface.

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But that’s only part of the puzzle.

Homemade radios

Although the group has been located, they are still in peril. The entrance to the cave remains flooded, and reports suggest that none of them are strong swimmers.

According to most reports, there are two options. The first is to try and teach the group how to dive and then attempt a risky swim to the surface. This would require specialist equipment – video footage from the cave has shown the boys already practicing with diving masks.

The other choice is waiting until the waters recede enough to clear a path. But that could take several months, and it’s only the start of the rainy season. In the last few hours, authorities have managed to drain part of the cave with pumps and pipes, reducing the water level by 40 per cent in a segment of the cave system . But there’s still a risk that the chamber where the group are stuck could flood.

There is one other rescue possibility – drilling. But, because the group are stuck in a relatively small space, between 800 and 1,000 metres below the surface, attempts to rescue them by drilling down would be very difficult without an extremely accurate measure of their location. “You’ve only got to miss them by a metre, and you’ve missed them by miles,” says Gary Mitchell, assistant chairman of the British Cave Rescue Council (BCRC).

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A rescue worker checks scuba tanks at a makeshift camp in Khun Nam Nang Non Forest Park in Thailand as divers prepare to install underwater lights on July 2 Linh Pham/Getty Images

Back in the UK, the BCRC – whose members John Volanthen and Richard Stanton were the first divers to make contact with the missing party – are trying to find a way to pinpoint the group’s location from the surface.

Another piece of homemade gear offers a potential solution, but it’s risky. The Pease system is a radiolocation kit that has been shown to be accurate through up to 300 metres of solid rock. Named after its inventor, cave radio enthusiast Brian Pease, it is assembled from off the shelf components, and could be quickly built in Thailand rather than being shipped over.

In theory, trained divers could swim such a system to the chamber where the group are stuck, where it could act as a beacon to guide a drilling team to their location. But that’s not so simple.

“We’re not saying it couldn’t work, but it would require a significant transmission and power source,” says Mitchell. “Normally in a small cave, it’s something like a 9-volt battery, but in this situation you’re talking about swimming a car or truck battery through the water.” Battery acid, electricity and water don’t mix well. “It’s risky, and it’s not something we’re prepared to ask the divers to do,” says Mitchell.

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For Slanvetpan, the most likely solution will be to lower the water level in the cave. As well as drones and robots, PTEPP have also been providing pumps, pipes, and engineering advice to help the rescue teams drain water from the area: up to 120 million litres of it in 75 hours.


“This is the equipment we use day in and day out,” he says – and it’s been a mixture of old and new technologies that have been instrumental in the rescue effort.

Drones and autonomous underwater vehicles may have captured the headlines, but radio kits made at home by tinkerers have been equally important in finding the lost football team.

It will take a similar combination to get them out safely. “Everyone is so delighted to see them alive, and to see them in good condition,” says Slanvetpan. “We can hardly wait to see them walking out from the cave – really, really soon.”