His knees slid between the rough flue pipes and ached. As he turned to crawl back to the manhole, he heard a noise above him, a metallic rattle, as though someone wearing a tool belt was crawling along the outside of the boiler. Before he could move all the way to the rear, he heard the manhole cover toll shut and the sound of the three-inch nut being hurried onto the single bolt that held the cover in place. When he got to the closed hole, he stared at the iron in disbelief, giving the head of the bolt a playful tap with his hammer as if to prove that it was real. The manhole cover was an oval plate that pressed against the inside of the boiler shell, held in place by a large bolt that ran through it to an exterior arch bar that pressed against the rim of the hole. The bolt was held fast by its nut, which was screwed against the arch bar.

Paul thought that someone must have made an innocent mistake. He banged on the boiler shell with a hammer to signal to whoever had shut him up. In response, hands and feet scuffled down to the forward end. Then nothing. It occurred to him that he had not been shut up by mistake, and he lay back on the rank of pipes, trying to think, trembling slightly when he realized that his first problem would be oxygen. Turning off his light to conserve the battery, he felt his tool belt and found four chisels, a heavy screwdriver, a twelve-inch crescent wrench, a small wire brush, and a foot-long scraping tool. He closed his eyes. The location of all the boiler fixtures appeared in his mind like a diagram: the water-supply pipe, the blow-off pipe, the water-level gauge. Sitting up, he felt along the arched top of the boiler for the opening to the spring-loaded safety valve, sliding his hand along the gritty steel until his fingers entered a cavity above his head. Turning on his light, he saw the three-inch-wide bronze valve seat. He drove the scraper against it, jamming it open. That would allow a thread of air to flow in, if he could find another opening. He scurried to the face of the boiler and pulled out his long-nose chisel, shining his light around until he found where two pipe nipples entered the side of the shell, probably coming from a water-level indicator. With the chisel he beat out the nipples in ten minutes, hearing a muffled racket as some device fell from the exterior and hit the floor of the boiler room. Putting his eye to the holes, he saw no light, so he pressed his mouth to the higher one and breathed. He found fresh air.