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“At first we didn’t think it was that serious,” Joon-hyuk said. But then the boat lurched further onto its side and the waters rose. “We heard the helicopters outside and told each other that the rescuers were coming.”

Joon-hyuk and his friends helped a young girl, not even 10 years old, don a lifejacket and hoisted her upward through a door, where rescuers were waiting. (Joon-hyuk believes she eventually made it back to shore.)

But Joon-hyuk and the other students were unable to reach the opening themselves, and began looking for another way out. The problem: by then, all other escape routes were blocked by water.

So Joon-hyuk and several other students took the plunge. In the murky water, there was no clear route to safety, so he felt his way around. Eventually he sensed an opening, swam through it and emerged into the open water. About 20 seconds after he surfaced, he was rescued.

“I wasn’t thinking about anything,” he said. “The only thing I was thinking about was coming back out of the water.”