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Experiments were carried out to study the effect of spacing between wall and thin fuels on upward flame spread. The front flame height, back flame height, pyrolysis height, burnout length, and pyrolysis spread rate were measured by video image analysis with spacings of 2 mm, 7 mm, 13 mm, 19 mm, and 25 mm. Experiments were performed on uniform PMMA (polymethyl-methacrylate) samples with 200 mm height, 50 mm width, and 1 mm thickness. The results are as follows: (1) As the spacing increased, the front flame height, back flame height, pyrolysis height, and burnout length showed the same trajectory, first increased and then decreased. The maximum trajectory was observed at a spacing of 6.5% of the wall height. (2) At an infinite length of PMMA, the pyrolysis zone and pyrolysis spread rate would reach an asymptotic steady state, and the pyrolysis and burnout spread rates will be asymptotically equal. (3) Of particular interest is the maximum mass-loss rate for a wall spacing/sample height ratio (0.065) due to enhanced the radiation fluxes. In this study, the effects of spacing between wall and fuels on upward flame spread was investigated for the first time using 1 mm thick PMMA sheets, including two-face burning case.

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The present paper studies the moisture effect on upward flame spread over cotton fabric by performing experiments using 0.245 mm thick, 180 cm tall and 10 cm wide sample sheets with moisture content ranging from 0% to 18%. As the moisture content increases, the flame height, pyrolysis height, burnout height, pyrolysis length and spread rate show the same trend, first increasing and then decreasing. The maximum value is observed in the case of the 2% moisture content samples. Furthermore, at an infinite length of fabric fuel, the upward flame propagation would reach an asymptotic steady state with constant pyrolysis length and spread rate. Finally, a higher moisture content corresponds to a lower flame temperature. For upward flame spread, the moisture content has the negative effects of increasing the thermal inertia parameters and reducing the flame temperature and heat feedback; simultaneously, the positive effect is that the moisture can enlarge the flame size and the effective preheating length. The combined effects of positive and negative effects result in the non-monotonous trend in the pyrolysis spread rate.