Liu Xin followed him up a hill on the north side of the valley, his confusion growing all the while. First, this was the safest direction, separated from the main seam by more than a kilometer. Second, Aygul had led him nearly to the top of the hill, but the curtain ring was far, far beneath them. What was there to go wrong here? When they reached the top, Liu Xin was about to gasp out a question when Aygul pointed in a different direction, to a place even farther off. Liu Xin laughed in relief—there was no disaster. The mine was directly ahead of where Aygul pointed, and between that hill and the one beneath their feet was an even slope that led to a meadow at the bottom. That was Aygul’s target. The mine and the meadow seemed peaceful at this distance, but after a longer look Liu Xin saw something strange about the meadow: in one circular spot, the grass appeared darker than the surrounding area, a difference only noticeable upon careful observation. He felt his heart seize, then he and Aygul raced down the hill to that patch of darker green.

When they got there, Liu Xin examined the round patch of grass, which had wilted to the ground as if it had been scalded. He put his hand on it and felt heat emanating from the ground. In the center of the circle a puff of steam rose in the light of the rising sun….

After a morning of emergency drilling and the dispatch of another thousand-odd ground rats, Liu Xin confirmed the nightmarish fact: the main seam had caught fire. The scope of the fire was unknown for the time being, since the ground rats had a maximum below-ground speed of around ten meters per hour. However, with the fire so much deeper than the test seam, the fact that its heat was radiating above ground meant it had been burning for quite some time. It was a big fire.

The strange thing was that the thousand meters of earth and stone between the main seam and the test seam was whole and unbroken. The ground fire had ignited on either side of the thousand-meter buffer zone, leading someone to suggest that it was unrelated to the experiment. But that was no more than self-delusion; even the person who had said it didn’t really believe the two weren’t in some way connected. Deeper exploration cleared up the matter late that night.

Eight narrow coal belts extended from the test seam. Only half a meter at their narrowest point, they were hard to detect. Five of them were bisected by the fire curtain, but the other three led downward and just skirted the curtain’s bottom edge. Two of these terminated, but the last one led directly to the main seam a kilometer away. All of them were actually ground fissures that had been filled up by coal; their connection to the surface provided them with an excellent supply of oxygen. The one linking the test seam and the main seam thus acted as a fuse.