White-orange fire churned beneath the floor grates of Sector 3. Heat bent the air above the observation rail.
A red sign hung over the entrance.
[SECTOR 03: HIGH-TEMPERATURE EXHAUST AND GAS SCRUBBING]
[DANGER: INCINERATOR EXHAUST. DO NOT CROSS THE FLOOR.]
[USE OVERHEAD SERVICE DUCT B-4.]
Austin studied the duct twenty-five feet above them. “That’s our route. Filtered air, insulated walls, and a straight path to the exit.”
The access ladder was locked by a rusted pin. He freed it with a bottle jack, then waited while Xiaoyao checked the rungs and Pug sniffed the open hatch.
Inside, the duct was barely wide enough for Pug’s shoulders. Austin went first with a temperature gauge. Xiaoyao followed with the tool bag and a coil of safety line. Pug came last, grumbling as his saddlebags scraped the metal.
For the first twenty meters, cool air moved over them. Then the fans slowed.
The temperature gauge climbed twelve degrees.
Austin raised a fist. “Stop. Airflow problem.”
A metal ticking sound ran along the duct. The fire below grew louder, and the insulated floor warmed under Xiaoyao’s knees.
He pointed to an intake grille behind them. Compact gray lint covered its mesh. “There.”
Austin brushed the grille once. Dust broke loose, but the mesh underneath remained packed solid. “Return filter’s blocked with three inches of lint. The fan can’t pull enough air through the duct.”
“Can we go back?” Xiaoyao asked.
“Not before the next inspection panel. The duct narrows behind you.”
The gauge climbed again. Sweat ran into Xiaoyao’s eyes. The metal around them began to ping as it expanded.
Austin opened the nearest service pouch. “We clear it here. Xiaoyao, hold the vacuum hose against the grille. Don’t let the dust cloud into the fan. Pug, keep your heads back.”
The little hand pump had been meant for sample bags, not a century of compacted lint. Xiaoyao sealed its hose against the grille with both palms while Austin worked a stiff brush across the mesh. Dust filled the hose. The bag swelled, wrinkled, and began to leak at the seam.
“Bag’s split,” Xiaoyao said.
“Keep the seal. I’ll patch it.”
Austin wrapped cloth tape around the seam while Xiaoyao held the hose steady. The fan changed pitch. Hot air pushed back through the grille, stinging his wrists.
He wanted to let go. Instead, he pressed harder.
The last strip of mesh came clear. The fan coughed, spun up, and pulled a clean current through the duct. The temperature stopped rising.
Austin checked the gauge. “Good seal. You kept it from getting worse.”
They moved on before the metal could heat again.
Fifty meters later, a warped support had pulled an insulation panel away from the ceiling. Orange light showed through the gap. The temperature beneath it was already too high for unprotected skin.
Austin wedged his back against one wall and lifted the panel with both hands. “I can hold it. I can’t fasten it from here.”
Xiaoyao crawled beside him, staying below the hot gap. He fitted a new clamp by touch, turned the screw with his fingertips, then used the small spanner when the angle grew too tight.
“One more quarter turn,” Austin said.
The clamp bit. Austin lowered the panel, and the orange line vanished.
They rested for thirty seconds in the moving air. Pug laid his middle head on Xiaoyao’s boot and panted. Nobody made a joke about the heat.
At the exit, the fan shuddered again. The sudden pressure change blew the grille inward before Austin could release its fasteners. Xiaoyao caught the edge with his safety line while Austin held the frame. Together they lowered it instead of letting it fall into the fire below.
Then they climbed out onto the cool exit platform.
The crossing had taken thirty-eight minutes. Austin’s sleeves were soaked. Xiaoyao’s palms were raw from the hose, and a gray stripe of dust crossed his face.
A terminal lit beside the door.
Austin wrapped two strips of clean cloth around Xiaoyao’s palms. “That was maintenance work, not a shortcut. You did well.”
Xiaoyao flexed his fingers. “The fire never touched us.”
“It didn’t have to. Heat, bad airflow, and loose metal were enough.” Austin looked back at the duct. “This is why you don’t ignore a rising gauge.”
Then the heat Austin had absorbed during the crossing gathered in his dantian. A deep golden hum shook the platform.