Experimental investigations of width effects and flame splitting phenomenon in upward flame spread over advertising canvas

Abstract

A series of comparative laboratory experiments were conducted to study the width effects and flame splitting phenomenon in upward flame spread. The test samples were 2.0 mm thick and 45 cm tall advertising canvas sheets with widths of 4.0–10.0 cm. The essential parameters including flame structure, flame height, flame spread rate and surface temperature were obtained by high definition video cameras and a thermal infrared imager. The major conclusions are summarized as follows: An unexpected but interesting phenomenon i.e. flame splitting, is observed in upward flame spread process, which is caused by multiple-step pyrolysis processes of the fuels. After flame splitting, the downstream flame propagates steadily to the end of the sample, while the upstream flame travels for a period time and then extinguishes. The temperature profile reveals four stages, including preheating stage, two pyrolysis stages and burnout stage, which demonstrates that the advertising canvas undergoes multiple-step pyrolysis processes in flame spreading. The maximum flame height before the flame splitting occurs, the flame heights for downstream and upstream flame after the flame splitting occurs and flame spread rate show an increase with sample width. The empirical models for flame height and flame spread rate taking sample width effects into account are established. These results in this paper are beneficial to scholars in better understanding the flame spread and fire growth of advertising canvas.