Flammability limit of thin flame retardant materials in microgravity environments

The flammability limits of thin flame retardant materials in an opposed flow under microgravity condition have been discussed by scale analysis. The predicted trends of flammability were verified by parabolic flight experiments. As the samples, meta- and pars-aramid fabrics (NOMEX and Kevlar), polyimide film (Kapton) and polycarbonate (PC) were investigated. In order to predict the limiting curve accurately, blow-off tests in high forced flow were conducted and the results were used to obtain proper pre-exponential factor, A, and activation energy, E, for blow-off phenomena. The blow-off tests revealed that the material with high pyrolysis temperature, such as Kevlar and Kapton, had its minimum limiting oxygen concentration (MLOC) at higher opposed velocity region. For such materials, it was predicted that the limiting oxygen concentration in microgravity environments was higher than that in normal gravity, and the prediction was consistent with the result of parabolic flight experiment. For NOMEX and PC, the limiting oxygen concentration increased monotonically with increase of opposed flow velocity. The developed model predicted that such materials could have their MLOC in microgravity environments. Actually, the MLOCs of NOMEX and PC were observed under microgravity condition and they were 2% and 0.5% lower than their limiting oxygen concentrations in normal gravity (LOC1g), respectively. The developed model with blow-off test data could predict the difference between the MLOC and LOC1g quantitatively, and it was found that the model was a good tool to discuss the flammability of the flame retardant materials in microgravity environments. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.