“Child,” one doctor said, looking straight into his eyes. “Your lungs have been seriously harmed. You’ll have to be hospitalized for at least a week. We’ll notify your parents.”

“Wait!” Seya shouted, his hands fumbling with the rebreather. “Did miners a hundred years ago wear these?”

“Shut your mouth and go to the hospital,” the teacher said. “Why can’t you ever just follow the rules?”

“We’re human, just like our ancestors. Why …”

Seya was shoved into the car before he could finish. “This is the first time the museum has had this kind of accident,” a doctor said severely, pointing at the teacher and adding, before getting into the hovercar, “This falls on you!” The hovercar left as silently as it had come.

We continued our tour. The chastened teacher said, “Every kind of work in the mine was fraught with danger, and required enormous physical energy. For example, these iron supports had to be retrieved after extraction in this zone was completed, in a process called support removal.”

We saw a miner with an iron hammer striking an iron pin in one of the supports, buckling it in two. Then he carried it off. Me and a boy tried to pick up another support that was lying on the ground, but it was ridiculously heavy. “Support removal was a dangerous job, since the roof overhead could collapse at any time …”

Above our heads came scraping sounds, and I looked up and saw, in the light of the mining lanterns, a fissure open up in the rock where the support had just been removed. Before I had time to react, it fell in, and huge chunks of holographic stone fell through me to the ground with a loud crash. Everything vanished in a cloud of dust.

“This accident is called a cave-in,” the teacher’s voice sounded beside me. “Be careful. Harmful stones don’t always come from up above.”

Before she even finished, a section of rock wall next to us toppled over, falling a fair distance in a single piece, as if a giant hand from the ground had pushed it over, before finally breaking up and raining down as individual stones. We were buried under holographic rocks with a crash, and our headlamps went out. Through the darkness and screams, I heard the teacher’s voice again.

“That was a methane outburst. Methane is a gas that builds to immense pressure when sealed in a coal seam. What we saw just now was what happens when the rock walls of the work zone can’t hold back that pressure and are blown out.”

The lights came back on, and we all exhaled. Then I heard a strange sound, at times as loud as galloping horses, sometimes soft and deep, like giants whispering.

“Look out, children! A flood is coming!”