Toxicity was not an evil spirit. It was a concentration of reactive chemical molecules in parts per million.
Inside the steel hull of Steam-Crawler Zero-One, Giles Croft adjusted the brass needle valve on the cabin make-up pipe hub.
Beside the jump seat, a high-pressure steel metal tube charged to two thousand pounds of pressure released a gentle, nonstop hiss of dry air into the air-flow duct. Overhead, a recirculating electric blower drew the cabin air through two heavy tube-shaped canisters filled with granular soda-lime and acid-washed activated coconut charcoal.
Giles tapped the glass dial of the cabin barometer.
The needle stood steady at one point one two sea-weights.
“Twelve percent above surrounding cave pressure,” Giles announced, writing the reading in his expedition journal. “The outward pressure differential is holding true.”
Before leaving the staging portal of Karak-Dum, Giles had conducted a thorough air-purge test.
He held a chemical smoke pencil along the seams of the two-inch thick quartz viewing ports and the outer edge of the double-gasketed airlock doors. The thin stream of white silver-steel tetrachloride vapor drifted smoothly outward. It curled away toward the door frame before being swept away by the positive inside draft.
