THRESHOLD COMPLEX EXPLORATION LOG

Designation / Log ID: 27-X24

Apparent Date/Time: 30 August 2026 / 02:14 (local) — secondary stamp reads 16:03 07 July 1954

Entry Method: Access hatch labeled “C-19 CT PLENUM”. Hatch opens upward. Threshold height measures 0.0 m on entry and 0.11 m on exit.

Environmental Baseline

Lighting: overhead vapor-proof fixtures, color temperature measured at 3800 K. Intensity constant at 92 lux.

Ambient temperature: 14.2 °C. Humidity: 81 %.

Background sound: continuous fan drone at 53 Hz. Amplitude 41 dB.

Air movement: downward draft of 1.1 m/s from ceiling registers. Barometric pressure 1008.7 hPa on entry; 1014.3 hPa after 18 m of travel.

Spatial Observations

Chamber estimated 31 m long by 11 m wide by 7.4 m high. Laser measurement returns 19 m long by 15.6 m wide by 6.1 m high.

Floor: grated steel over concrete sump. Grate temperature 3.8 °C below ambient.

Walls: concrete with residual mineral staining. Stain patterns remain fixed after three passes.

Ceiling: exposed fan housings and drift eliminators. Fan inventory returns 6 discrete units. Visual count remains fixed at 6 after five passes.

Repeating motif: every 3.7 m a water-level sight glass is mounted at 1.6 m height. Sight glass faces measure 0.18 m by 0.45 m. Water column height is identical across all units.

Anomalies

Visual inventory of active cooling fans returns 6. Physical inventory returns 6. Fan blade clearance measures 0.4 m while housing depth measures 1.2 m.

Floor remains level under spirit level. Measured water surface in the basin slopes 2.3° toward the south wall. Slope reverses after 5 minutes of continuous observation without change in physical orientation.

Basin water temperature measures 4.1 °C while ambient air remains 14.2 °C. No frost forms on any surface.

Fan rotational speed at primary unit measures 0 RPM while motor current is fully engaged. Motor housing temperature measures 52.7 °C regardless of ambient.

Sound of water droplet impact arrives 2.1 seconds before corresponding vibration is detected at the grate. Delay increases by 0.35 s for every additional 3.5 m of distance from the north wall.

Humidity at mid-chamber remains 81 % while condensation forms on the sight glass faces after 6 minutes of observation. Condensation evaporates without measurable change in local humidity.

Entity Notes

None observed.

At the 13 m mark a localized pressure drop of 4.2 hPa occurs across a 2.4 m radius. Drop persists for 14 seconds then collapses. No visible source or airflow change accompanies the event.

Exit / Continuity Status

Exit achieved by retracing path to the access hatch. Hatch released with moderate resistance.

Exterior time on exit: 03:01 local. Elapsed interior time: 47 minutes. Wristwatch confirms same interval.

Residual effects: residual fan drone audible for 13 minutes after exit. Temporary inability to resolve water column height beyond 1.8 m lasting 9 minutes. No other reported sequelae.