Numerical Investigation of the Thermal Exposure of Façade During BS 8414 Test Series: Influence of Wind and Fire Source.

Evaluation of a specific facade system's fire performance can be undertaken using large-scale testing, following the local regulations. The fire test protocol detailed in BS 8414 series is representative of an external fire source, or a fully developed (post-flashover) fire in a room, venting through an opening such as a window that exposes the façade to the effects of external flames. This test can be performed indoors or outdoors, with a wind or air velocity of less than 2 m/s. However, wind can have significant effects on the external flame shape, and thus on the thermal exposure of the tested façade. According to the testing conditions given in BS 8414 series, the test uses a wood crib as a fire source with Heat Release Rate between 2.5 MW and 3.5 MW (3.0 ± 0.5 MW). In this paper, a numerical model of the BS 8414 facility is validated based on experiments for an incombustible façade system. Then, the influence of the wood crib contribution on the heat exposure is investigated numerically, using three different values of the wood crib HRR. It was thus shown that the uncertainty allowed for wood crib HRR in BS 8414 with a peak rate of (3.0 ± 0.5) MW and up to 4 MW had no significant influence on the temperature results achieved for the calibration system, but had an impact on the heat flux imparted to the walls for the lower HRR value. The effect of an external wind with three different directions is addressed in terms of variation of the thermal exposure on the façade. A strong impact was observed in terms of patterns of fire exposure and flame height. [ABSTRACT FROM AUTHOR]