TEMPERATURE DISTRIBUTION IN THE VICINITY OF VERTICAL WALL ON OPENING FIRE PLUME EJECTED FROM HORIZONTAL OPENING

Abstract

 Fire plume ejected from an opening tend to have a central axis of air current that rises closer to the wall surface as the cross-sectional shape of the opening (hereinafter , horizontal opening) becomes more horizontal. Fire plume ejected from such openings increase the potential risk of fire spreading to upper floors. Furthermore, fire plume from an opening may become longer due to increased thermal decomposition of combustible materials inside the compartment and the effect of pyrolysis gas burning outside the building.
 Currently in building design practice in Japan, the method proposed by Yokoi is generally used when investigating measures for preventing the spread of fire to the upper floors due to fire plumes from openings in buildings. However, the opening conditions that Yokoi examined covered aspect ratios n = 2W/H (W: width of opening; H: height of opening) of up to around 6.4, whereas the openings in modern buildings may have openings with aspect ratios greater than 6.4. Furthermore, although the amount of pyrolysis gas emitted from the opening is expected to increase with increased amounts of flammable material brought into the building, the Yokoi method is unable to take into account such changes in the amount of pyrolysis gas.
 The focus of this research was therefore placed on the shape of the plumes of hot air under various flammable material conditions for openings with a horizontal shape. A series of experiments using a full-size compartment focusing on the shape of the temperature distribution in order to obtain knowledge related to the shape of the temperature distribution were conducted.
 In the experiment, we aimed to determine the temperature distribution above horizontal openings with aspect ratios of n = 5~20. The experimental apparatus consisted of a combustion compartment and a facade for modeling a room on fire. The dimensions of the combustion compartment were 4000[mm] wide × 4000[mm] deep × 1700[mm] high. The shape of the opening was fixed with opening widths of 2[m] and 3.7[m], and the opening aspect ratio was set in the range n = 5~20 in six sets of conditions for the opening width of 2[m] and three sets of conditions for the opening width of 3.7[m]. Three different fuels were used for the heat source: methanol, ethanol, and heptane.
 The following was found from this study.
 · Temperature attenuated with height Z above the opening to essentially the -1 power, the same as the gradient of the temperature distribution of the rectangular heat source.
 · The temperature distribution near the wall above the opening, nondimensionalized by taking T^* for the vertical axis and Q^*_(H-Zn)^-2/3z_(H-Zn)^* for the horizontal axis, exhibited a correlation with the temperature distribution of the rectangular heat source in free space when using the amount of heat Q_ef generated by pyrolysis gas.
 · Q_ef,max may underestimate the amount of heat generated by the pyrolysis gas. When Q_ef,crit was used, under the conditions where ethanol and heptane were used, the calculated and experimental values tended to match well.