The boys’ coach, Ekkapol Chantawong, wrote to the parents as a group, promising to take care of them as best as he could. The parents had written to him earlier, assuring him that they did not blame him for the situation.
“Thank you all for the support,” the coach wrote. “I deeply apologize to the parents.”
He also wrote to his own family members — an aunt and his grandmother — asking them not to worry too much about him. “Aunty, can you please tell granny to prepare vegetable juice and pork snacks?” he wrote. “I’ll eat them when I get out. Love you all.”
— Muktita Suhartono, at the Tham Luang Cave
Why a 15 percent oxygen level has rescuers worried
On Friday, a Thai Navy SEAL commander said the oxygen level in the boys’ cavern was about 15 percent and falling. That is a concern because levels below 16 percent can cause oxygen depletion, a condition known as hypoxia.
Under normal conditions, the air people breathe consists of about 21 percent oxygen, 78 percent nitrogen and one percent argon and other gases, including carbon dioxide. When the mix changes, humans can feel a range of health effects, subtle and otherwise.
The U.S. Federal Aviation Administration reports that hypoxia may cause headaches, nausea, drowsiness, rapid breathing, slurred speech and “diminished thinking capacity,” among other problems. It can also result in incapacitation or, in extreme cases, death.
Hypoxia can be a concern in high-altitude regions, or when a plane loses air pressure.
The air in caves tends to be good, and cavers would typically worry about high concentrations of carbon monoxide, not low concentrations of oxygen, said Dinko Novosel, the president of the European Cave Rescue Association.
But Mr. Novosel said an oxygen concentration of 15 percent or less in the Tham Luang Cave network would be “really problematic” for anyone trapped inside. It would allow them to survive, but make even basic activities difficult, he said.