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Self induced buoyant blow off in upward flame spread on thin solid fuels

Johnston, Michael C., T'ien, James S., Muff, Derek E., Zhao, Xiaoyang, Olson, Sandra L., Ferkul, Paul V.
Fire safety journal 2015 v.71 pp. 279-286
air, cotton, fabrics, fiberglass, fuels
Upward flame spread experiments were conducted on long thin composite fabric fuels made of 75% cotton and 25% fiberglass of various widths between 2 and 8.8cm and lengths greater than 1.5m. Symmetric ignition at the bottom edge of the fuel resulted in two sided upward flame growth initially. As flame grew to a critical length (15–30cm depending on sample width) fluctuation or instability of the flame base was observed. For samples 5cm or less in width, this instability lead to flame blow off on one side of the sample (can be either side in repeated tests). The remaining flame on the other side would quickly shrink in length and spread all the way to the end of the sample with a constant limiting length and steady spread rate. Flame blow off from the increased buoyancy induced air velocity (at the flame base) with increasing flame length is proposed as the mechanism for this interesting phenomenon. Experimental details and the proposed explanation, including sample width effect, are offered in the paper.