Rescue teams at Tham Luang have taken up a new challenge of feeding a 5-kilometre air tube into the partially flooded cave complex to pump fresh air in after oxygen levels fell to 15%, posing a health threat to the 12 young footballers and their coach.
The oxygen issue raises new concerns for the group who are currently being nursed by a medical team after being located by divers on Monday night.
It is believed that the large number of rescue workers in the cave has contributed to the reduction of oxygen.
At yesterday's press conference, Naval Special Warfare Command chief Rear Admiral Apakorn Yukongkaew said laying the air pipe to provide more oxygen, coupled with communications cables, also carries significant risks.
In early hours of yesterday morning, Petty Officer 1st Class Saman Kunan, a Navy Seal, reportedly died from a lack of oxygen, according to Chieng Rai provincial deputy governor Phatsakon Bunyalak.
Petty Officer 1st Class Saman was part of the team trying to install the air pipe, according to Chiang Rai provincial deputy governor Phatsakon.
Rear Adm Apakorn allayed concerns about the group's health, saying the young football team is under close medical supervision.
Rear Adm Apakorn said it is 12-hour journey for the divers who have to snake along the 1.7km distance between the forward command centre at Chamber 3 and Nern Nom Sao Slope where the boys are. The passage is narrow with bends and flooded with murky water.
"This is an unprecedented situation but we have to accomplish the mission and adjust our plans as circumstances change," he said, adding that navigating the flooded cavern is still the only way to reach the group.
With more rain looming this weekend, rescue teams continue to work around-the-clock to drain water from the partially flooded cave hoping to lower the water level to the point where the 13 can be extracted without risks.
Army commander Chalermchai Sitthisad said yesterday whether or not the evacuation will go ahead depends on a number of factors – from the readiness of the rescue teams to the readiness of the boys to dive.
Interior Minister Gen Anupong Paojinda said yesterday a drilling mission to reach the group from above is expected to begin this morning.
However, he said they would wait for the assessment from a British team, which was expected to arrive late last night.
"The prime minister has agreed to [the idea of drilling], and we have the equipment to proceed. But let's see the assessment first. If the team says it's best to remain in the cave, they stay.
"But if they say the water is dangerously high, a decision will be made," added Gen Anupong.
Meanwhile, tech billionaire Elon Musk was sending specialist engineers to Thailand to help aid the rescue.
Musk, founder of the Boring Company, as well as CEO of Tesla and SpaceX, tweeted that: "SpaceX & Boring Co engineers headed to Thailand tomorrow to see if we can be helpful to govt. There are probably many complexities that are hard to appreciate without being there in person."