THRESHOLD LOG 09-F6

Designation: Ventilation Plenum V-9

Apparent timestamp: 04:03 / 17:51 / 04:03

Entry method: Access hatch from adjacent service corridor

Environmental Baseline

Diffused fluorescent panels, 3500K, intensity 90 lux with irregular 1.8-second dimming cycles.

Ambient temperature 19.1°C. Humidity 71%.

Air pressure 0.8% below external baseline. Continuous low-velocity airflow from overhead grilles registers as still air on exposed skin.

Background sound consists of distant fan noise delayed by 2.7 seconds relative to visible grille movement.

Spatial Observations

Plenum measures 14.3 m long by 3.8 m wide by 2.1 m high. Measured length after full traversal: 11.6 m.

Floor: galvanized metal grating over dark void. Grating sections measure 1.2 m × 0.6 m. Counted sections total 47. Calculated coverage requires 38.

Walls: unfinished concrete with horizontal conduit runs at 0.9 m and 1.7 m heights. Conduit junctions repeat every 2.4 m.

Ceiling: dense array of rectangular supply grilles. Grille faces point downward. Airflow direction reverses when observed from opposite ends of the plenum.

Access hatches appear on both long walls at 4.1 m intervals. Hatch dimensions are uniform (0.7 m × 0.9 m). All hatches open into identical short corridors of 1.8 m length that terminate in blank concrete.

Anomalies

Air temperature at floor level is 3.4°C higher than at ceiling level. Temperature gradient inverts when facing the opposite direction.

Fan noise lag increases by 0.4 seconds every 30 seconds of continuous presence, then resets.

Grating sections produce no sound under footfall. Footfalls register 1.1 seconds later from a location 3 m behind the walker.

Attempting to measure plenum height with a laser rangefinder returns alternating values of 2.1 m and 3.6 m on successive pulses. Physical tape measure remains consistent at 2.1 m.

Elapsed time on recording device is 28 minutes. External chronometer shows 9 minutes elapsed.

Hatches close autonomously after 90 seconds if left open. Closing produces no mechanical sound.

Entity Notes

None recorded.

Exit / Continuity Status

Exit achieved through original access hatch after 31 minutes subjective.

Hatch position relative to internal landmarks shifted 2.3 m along the wall during the final approach.

Residual effect: residual delay of 0.6 seconds between visual and auditory events persists for 14 minutes after exit.

Recording device battery drain is 1.7× expected rate.