Experimental study of welding region effects on upward flame spread over textile membranes

Abstract

Textile membranes are used widely as a main architectural material in membrane structure buildings. However, very few studies have been conducted to investigate the flame spread characteristics of textile membranes, especially in the case of upward flame spread. In this paper, the effects of welding region on upward flame spread were investigated experimentally using sample sheets of textile membranes 60 cm tall and 6 cm wide with and without welding region. The corresponding observations are as follows: the width of flame with welding region is narrower than that without welding region; flame height, pyrolysis height, preheating length, flame length, and pyrolysis spread rate decrease significantly in the presence of a welding region, while ignition time increases; flame temperature decreases in the presence of a welding region, and temperature along the welding region is higher than that near the edge. The welding region effects are as follows: in presence of a welding region, the thickness of welding region increases and, accordingly, ignition time shows an increase, leading to relatively low pyrolysis gas generated per unit time and relatively less heat released; in addition, a relatively larger pyrolysis gas concentration gradient over the width for welding membranes results in a relatively stronger air entrainment occurring at the sample sides, taking away part of the heat flux and narrowing the flame width. Thus, the presence of a welding region has negative effects of increasing ignition time and reducing preheating length on upward flame spread over textile membranes, eventually decreasing the pyrolysis spread rate.