Experimental study on downward flame spread characteristics under the influence of parallel curtain wall

In this paper, experimental methods and theoretical analysis are employed to investigate effects of parallel curtain wall on downward flame spread characteristics of insulation materials on building facade. As the curtain wall spacing (D) rises, the front surface of facade flame becomes more irregular. For small spacing, the flame stretching phenomenon is obvious and periodical change of the flame height is observed. The average flame height (Hf) first drops and then rises as the spacing increases. The variation of Hf is significant as D ≤ 11.5 cm while indistinctive change is observed for D > 11.5 cm. The average maximum flame temperature first rises and then drops as D increases. There is a power function relationship between internal surface temperature of the curtain wall and D. The total heat feedback from the curtain wall to the facade decreases exponentially with the rising of D. A formula is proposed to predict the radiant heat feedback from the curtain wall, which is more dominant than the convective heat feedback. As D rises, the radiant heat feedback decreases, while the ratio of convective heat feedback to the total first rises and then drops. With the increasing of D, the average flame spread rate first rises and then drops, which is attributed to the competition of negative effect and positive effect of the curtain wall.