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!”

We were still processing what she said when a broad surge of water erupted from a tunnel not far away. It quickly swamped the entire work zone. The murky water reached our knees, and then was waist-high. It reflected the light of our headlamps to shine indistinct patterns on the rocky ceiling. Wooden beams stained black with coal dust floated by, and miners’ helmets and lunch boxes…. When the water reached my chin, I instinctively held my breath. Then I was entirely underwater, and all I could see was a murky brown where my headlamp shone, and air bubbles that sometimes floated up.

“Mine floods have many causes. Whether it’s groundwater, or if the mine has dug into a surface water source, it’s far more life-threatening than a flood above ground,” the teacher said over the sound of the water.

The holographic water vanished and our surroundings returned to normal. Then I noticed an odd-looking object, like a big metal toad puffing out its stomach. It was huge and heavy. I pointed it out to the teacher.

“That’s an anti-explosion switch. Since methane is a highly flammable gas, the switch suppresses the electric sparks that ordinary switches create. That’s related to what we’ll see next, the most terrifying mining danger of all …”