A computational study on effect of horizontal openings on fire dynamics within informal dwellings

Fires in informal settlements are a major risk facing big cities within developing countries, not only concerning life safety but also because they exert social and economic pressures on these communities. An international research project, namely IRIS-Fire [1], was launched in order to develop fundamental understanding of the technical issues regarding fire spread within the informal settlements of the Western Cape, South Africa. Experiments conducted within the project, have shown that fire spread between dwellings mainly occurs through direct flame impingement from the openings of the burning dwellings to adjacent structures, as shown in Fig. 1 (a). Therefore, it is hypothesised that finding a way to decrease the intensity of the flames impinging on adjacent structures from the burning dwelling post flashover, and increasing the time to flashover within the dwelling, could decrease fire spread within settlements.
This paper, therefore, is proposing –computationally- a new design intervention for the dwellings’ roofs by adding horizontal openings to relieve the smoke accumulation before flashover, thus prolonging the time to flashover and releasing some of the burning gases (flaming) from the roof openings after flashover. This is hypothesised to reduce the size and intensity of the flames thus reducing spread between dwellings and can in principle decrease the critical distance. This paper will explicitly examine; time to flashover; heat flux from the openings; and the average flame length (and temperature) whilst varying the fuel load and size of the horizontal openings in the roof. To facilitate the study and the future comparisons with literature, an ISO-9705 room sized dwelling has been conceptualised, with one window and door on one of the long sides of the compartment as shown in Fig.1 (b). In this computational work the fuel loads were as follows: 270 MJ/m2, 410 MJ/m2, 550 MJ/m2 and 690 MJ/m2, which were represented by wood cribs distributed on the floor area. Twenty different cases were investigated using the four assumed fuel loads and four horizontal openings with total sizes of 0.04, 0.16, 0.32 and 0.64 m2, as shown in Fig. 1.(c).