The Microgravity Smoldering Combustion (MSC) experiment is a study of the smolder characteristics of porous combustible materials in a microgravity environment. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder for the purpose of control and prevention, both in normal- and microgravity. Recently, one opposed forced flow test using air as oxidizer and one forward forced flow test with air as oxidizer, were conducted aboard the NASA Space Shuttle (STS-105 mission). In this work we are reporting the opposed flow smolder results, since it is in this smolder mode that previous microgravity tests were conducted. A comparison of the tests conducted in normal- and microgravity indicates that there is a critical oxidizer mass flux to attain a self-propagating smolder reaction, and that this critical mass flux is significantly smaller in microgravity than in normal gravity. This finding has important implications from the point of view of fire safety in a space-based environment, since smolder can be initiated at lower oxygen concentrations or mass flows than in normal gravity.
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