Experimental investigation on the rising characteristics of the fire-induced buoyant plume in stairwells

A set of burning experiments were conducted in a 1/3 scale stairwell to investigate the rising characteristics of fire-induced buoyant plumes in stairwells. Results show that the time for the front of a buoyant plume to reach a given height from a fire source is inversely proportional to the 1/3 power of the heat release rate and proportional to the 1.203 and 2.129 power of the height in the stairwell with top vent open and closed, respectively. The relations between dimensionless rise-time of fire plume front and dimensionless rise-height in stairwells are proposed to predict rise time of fire plume fronts. The vertical distribution of temperature in the stairwell with top vent open at steady state was investigated and results show that the attenuation coefficient is inversely proportional to the mass flow rate in the stairwell. Discharge coefficient of the stairwell was calculated based on the air velocity at the openings of the stairwell and the temperature distribution in the stairwell. The average value of discharge coefficients is 0.23, indicating larger resistance to influence the rising of fire plume in the stairwell due to the block of the stairwell treads.