Experimental and Numerical Investigation of Smoke Transportation Characteristics and Flame Self-Extinction in Sealed Underground Deep Vertical Space

Underground deep vertical spaces are a new form of architectural structure for the efficient use of land resources. However, their slender geometry can intensify smoke transport and thermal hazards during fires. Sealing is a potential emergency strategy, but its influence on smoke dynamics and flame extinction in deep shafts remains insufficiently quantified. This study investigates smoke transportation characteristics and flame self-extinction in a sealed deep vertical space using 1:26 reduced-scale experiments combined with CFD simulations. Across the tested conditions, sealing consistently increased the characteristic upper-shaft centerline temperature rise, with enhancements ranging from 43.2% to 374.9%. The vertical centerline temperature above the fire exhibits a segmented decay behavior: in the plume-rise region it follows a power-law trend, while the decay coefficient deviates from the ideal-plume expectation, consistent with the thermal shielding effect associated with the confined upper hot-gas layer. Under sealed conditions, a distinct “ghosting” flame behavior and eventual self-extinction were observed. The combined flame, thermal, and simulated flow-field evidence is consistent with an oxygen-limited interpretation, although this mechanism was not directly verified by gas-species measurements. Based on the reduced-scale dataset, the self-extinction time was normalized by the characteristic oxygen-consumption timescale to2, yielding texttO2=2.074h1 m−0.394Q1 kW−0.071, which provides a quantitative description of flame self-extinction under the tested sealed conditions.