The Venting Grates and the Thermal Draft

Crouched in the pitch-black storage alcove with the ledger clutched tight against her chest, Lyra froze as the draft around her ankles suddenly shifted. Instead of the cold, stagnant damp of the subterranean tunnels, a heavy, furnace-warm gust swept upward from the floor grates, carrying a dry, mineral-laden grit and the sharp, chemical reek of scorched oil. The sudden temperature spike made the damp leather of the pressure-release ledger warp slightly in her fingers, highlighting the dangerously rapid escalation of pressure taking place in the conduits just beyond the stone wall.

As the heated air continued to waft up from the floor grates in her alcove, Lyra watched in the dim gloom as a fine layer of dust on the flagstones began to part under a steady trickle of warm, oily vapor. The creeping mist left a thin, viscous film of dark silt settling slowly over the toes of her boots, signaling that the pressure-release channel directly beneath her feet was actively venting. With the masonry groaning under the thermal strain, the margins for a controlled manual intervention were shrinking by the second.