KATHMANDU, Nepal — On a frozen lip of rock near the summit of Mount Everest, the climber Adrian Ballinger watched as his teams’ oxygen regulators failed, one after another.

Several of them hissed, swiftly expelling oxygen from cylinders carried by the hundreds of climbers who scale the world’s highest mountain every year. Others shot plumes into the sky “like fireworks,” Ballinger said.

Panic spread among the 25 climbers. Of the group’s few dozen regulators, which sit atop cylinders and control the flow of oxygen, nine failed in less than an hour during their expedition last spring, he said.

“This was by far my most dangerous day on the mountain,” said Ballinger, who has been leading Everest expeditions for over a decade.