Yan entered the service passage to reach the main valve. Heat pressed at his face, though the hall behind him was still cool enough to breathe in. The gauge beside the door ticked in uneven bursts. Its needle jumped past the red line, dipped, and jumped again.
Assistant Fen came after him with a wrench. Qinghe reached the entrance from the herb lane and caught Fen’s sleeve.
“Back to the hall,” she said. “Clear the public side. Yan, what is blocking the valve?”
“A crate under the handle. I can move it, but I need the wrench and the path kept open.”
Qinghe looked past him. The crate of clinic herbs stood against the passage wall, its wrapping already warm. The service route was too narrow for people to pass while Yan worked.
“Fen, take the public aisle. Tell Zhao to stop the demonstration and move the clerks out.” Qinghe released her sleeve. “I’ll hold this doorway.”
Fen took two steps, then glanced at the needle. “Zhao says the pressure is stable.”
“It’s above the marked line,” Yan said. “You saw it.”
Fen looked at the service mark on the gauge mount. “I saw it. I’ll clear the hall.”
She ran back. Qinghe stayed at the threshold with one hand on the warm herb crate, keeping it from rocking as the floor trembled. Yan moved farther into the passage. He could hear Zhao speaking over the crowd, describing the medicine’s color and yield as if the furnace were behaving exactly as planned.
A cart wheel scraped behind him. Bai Jiu came in from the public gate with a small local delivery box for the infirmary, its paper label still tied to the handle. He saw the workers moving and set it down well away from the hot passage.
“What’s happening?”
“The batch may rupture,” Yan said. “Take the apprentices toward the side arch. Don’t bring anything back through here.”
Bai glanced at the delivery. “The infirmary needs those jars.”
“They can wait.”
Bai pulled the box clear of the doorway and turned toward the apprentices. Two had stopped to watch the furnace through the hall’s open interior door. The glow behind the glass had gone from red to a hard orange. He stood between them and the passage.
“You heard him,” Bai said. “Move.”
One boy frowned. “My coat’s on the bench.”
“Then it will be there later. If the roof comes down, you won’t need it.” Bai pointed to the side arch. “Go with Qinghe.”
The boy started, then the younger apprentice beside him grabbed his sleeve and pulled him along. Qinghe formed a line at the threshold, sending people through one at a time so they would not collide at the narrow turn. Bai counted them aloud. Fen appeared at the far side of the hall, waving the workers away from the demonstration table.
“Stay to the wall,” Qinghe called. “Leave the tools and trays. Keep the arch clear.”
A clerk tried to turn back for a ledger. Bai caught the loose edge of his robe.
“You can write a new page,” he said. “You can’t replace your lungs.”
The clerk scowled, but he followed the line. Qinghe marked names against the inspection slate as they passed. She did not shout unless someone tried to break from the line. The passage remained hot, but the door stayed clear enough for Fen to bring the longer wrench.
Yan found the valve handle beneath a low crate wedged against the wall. He pressed his left shoulder into it and pushed. The crate shifted a few inches, then caught against the metal conduit. His right arm stayed tucked close under his sleeve. The healing upper-arm cut pulled when the crate dragged, but the bandage held. The old bruise answered with a dull ache.
He set his feet wider and pushed again with his legs and shoulder. The crate rolled enough for him to reach the valve wheel. He tested it with his left hand and pulled back at once. The metal was too hot to grasp barehanded.
A wet sack hung from a hook. Yan wrapped it around the wheel and tugged once. The cloth began to steam. He folded a second layer over the handle and tried again, careful not to press the hot fabric against his palm. The wheel moved a fraction. Something inside the valve clicked and locked.
The gauge ticked faster. Yan released the wheel and stepped away. The scorch line across the vessel seam had lengthened. It was no longer a thin mark; a black edge curled from the metal where the heat had eaten through the surface.
Fen returned with the long wrench. “Qinghe says keep the route open.”
“Then stay on the outer side.” Yan made room for her. “If it slips, don’t brace against the wall.”
Fen wrapped her hands in spare cloth and fitted the wrench over the wheel. They pulled together. The teeth slipped with a sharp crack, and Fen was thrown sideways into the wall. She landed on one knee, unharmed, but the wrench bent at the end.
Yan caught the handle before it hit the floor. Fen shook out her arms. “It moved.”
“Not enough.” He looked at the bent teeth. “The wheel is slipping inside the valve.”
“We can try the shorter wrench.”
“No. We’ve already seen what happens when it catches.”
A tremor ran through the passage. Dust sifted from the overhead pipe. Yan checked the route behind him. Qinghe was still directing clerks through the side arch; Bai’s count carried from the yard.
Fen reached for the bent wrench. “If I can get a better angle—”
The vessel gave a low groan that vibrated through Yan’s soles. He put a hand out to stop her.
“I’m done with the valve. We’re leaving.”
Fen opened her mouth, but a second sound rolled through the passage, deeper than the first. A fresh crack spread from the scorch line. Yan took the wrench and backed toward the doorway with her. He did not make another attempt.
Smoke began to push under the hall door. At the threshold, Qinghe turned the last clerks toward the side arch. Yan handed her the bent tool.
“The teeth slipped. It won’t turn.”
“Is Fen hurt?”
“No,” Fen answered for herself. She flexed her fingers. “The wall caught me.”
Qinghe looked at her hands, then at the growing smoke. “Stay with the group.”
Steward Lu remained beside the demonstration table with the inspection tablet. He called names while clerks answered from the outer yard. Yan could see the side arch was clear, yet people still hesitated near the center aisle, waiting to hear whether the demonstration was over.
Bai came back to the doorway only long enough to guide an apprentice who had frozen by the wall. The small delivery box remained where he had set it, away from the hot passage.
“Keep going,” Qinghe called. “No one comes back for a bag or a tool.”
The vessel shuddered again. Steward Lu checked the names on his tablet against the people outside, and Qinghe counted them again from the arch. Several assistants were still crossing the central aisle. Yan held the bent wrench at his side. The passage had cleared, but the hall had not. He heard the casing crack once more and backed toward the side arch as the next group began to move.