The investigation of flame length and flow field structure in the underground vertical channel with different opening areas

•The flame length of pool fire in underground vertical channel has been studied.•The rocking and forking flame can be found since vortex exists in the vertical channel.•The flame length in underground vertical channel is lower than that in open space.•A correlation of flame length in vertical channel has been obtained under different opening areas and distances. This study presents a quantitative analysis and interpretation about the effects of natural air flow, opening size and fire location on flame length in the underground vertical channel like car elevator or staircase. The gas burner of 0.1 × 0.1 m with five heat release rates (HRR) is used and eight locations are considered in 1/7 scale model. The air flow structure inside the vertical channel is investigated by CFD simulation. Hydraulic diameter and a characteristic length is proposed to calculate the flame length. A specific correlation between the flame length and dimensionless HRR is established to estimate the degree of fire disasters in the vertical channel with different opening size and locations.