Limiting Conditions for Flammability of Polymers

Limiting oxygen index (LOI) is commonly used to evaluate flammability of polymers. The accepted test standards are ASTM G 125 and D 2863. The data provided by these standards, however, may not correlate closely with many real-life fire scenarios. Two of the most common issues are the direction of flame propagation recommended by the standard method and the test environment temperature. The standard test methods recommend testing samples at room temperature and in a downward flame propagation mode. Modifications of these two parameters could render most polymers flammable; however, these same polymers would, under standard testing conditions set forth by ASTM G 125 and D 2863, be considered nonflammable. In this study, standard and modified LOI tests were conducted on 16 polymers to determine the magnitude of these effects. The results indicate that the LOI data commonly presented in the literature should be used with caution. Potential applications for next-generation flight vehicles, such as the Crew Exploration Vehicle (CEV), include optimization of materials selection from a flammability standpoint. In addition, the method would generate data useful under various spacecraft oxygen and temperature conditions, and allow quantitative flammability correlations between normal gravity and microgravity or partial gravity conditions.