Citation

Tu R, Ma X, Zeng Y, Zhou X, He L, Fang T, Fang J. Build. Environ. 2019; 164: 106339.

Copyright

(Copyright © 2019, Elsevier Publishing)

DOI

10.1016/j.buildenv.2019.106339

PMID

unavailable

Abstract

Downward flame spread over polymer materials is one of the typical hazardous scenarios in building fires, and also an important feature for fire safety research. This work was motivated to study the coupling effects of ambient pressure and orientation on downward fire propagation with a widely used thermal insulation polymer, flexible polyurethane (FPU). Comparative experiments were conducted under 3 different pressures (75 kPa, 80 kPa and 100 kPa) and 4 angles of inclination (0°, 30°, 60°, 90°) respectively, to investigate the variation of fire characteristics including flame tilt, length, spread velocity, burning rate, and related heat transfer mechanisms. The results showed non-monotonic tendencies of these parameters with enlarged inclination angle, and more complicated relationships by coupling pressure effect. Flame tilt was found be determined by the asymmetric entrainment induced, and also a key factor controlling heat preheating mechanism. Variation of spread velocity and consequent burning rate and flame length were discussed theoretically based on different preheating heat fluxes including convection, radiation and conduction from fire and solid phase. Particularly, a semi-quantitative correlation for coupling effects of pressure and inclination on flame spread velocity was proposed, which could help to improve the understanding of fire evaluation under low pressures.

Language: en

Keywords

Flame spread velocity; Flexible polyurethane; Heat transfer mechanism; Inclination; Low air pressure