Fu-Yu Hshieh

Evaluation of polyimide foam as a fire barrier for spacecraft cushion materials

Polyimide foam is an intrinsically flame resistant foam material. This study uses the NASA upward flame propagation test and the cone calorimeter test to evaluate the application of polyimide foam as a fire barrier for spacecraft cushion materials. The flame propagation test results demonstrate that a thin-layer of polyimide foam (3-mm thick) could totally stop the flame spread on the underneath polyurethane foam in an environment containing 30% oxygen. The cone calorimeter test results show that polyimide foam increased the minimum heat flux for ignition of a cushion sample from 27 to 48kW/m2. This suggests that application of polyimide foam can significantly reduce the ignition risk. It was also found that polyimide foam significantly reduced the peak heat release rate, mass burning rate, and the generation of carbon monoxide and smoke in the flaming combustion. For polyimide foam-covered polyurethane, smoldering combustion was insignificant at 25 and 35kW/m 2 incident heat fluxes; it became more important when the incident heat flux reached 45 kW/m2. The smoldering combustion of polyurethane foam and polyimide foam-covered polyurethane could not be self-sustaining if the external heat source was removed.

Closed-cup Flash Points and Flammability Properties of Selected Chemical Compounds

The closed-cup flash points of nine organic compounds and 38 organosilicon compounds are measured using a Setaflash closed-cup tester. This study demonstrates that Setaflash closed-cup tester is an effective tool for measuring the flash points of combustible liquids, especially for high-viscosity liquids. The flammability properties of these chemical compounds are determined using a cone calorimeter at a low-incident heat flux of 3 kW/m2. The results show that good correlations can be found between the closed-cup flash point and the time to ignition, the time to peak heat release rate, and the propensity to flashover. There is no good correlation between the closed-cup flash point and the peak heat release rate.

Carbon dioxide Fire suppressant concentration needs for International Space Station environments

Fire suppression onboard spacecraft is a critical issue. Currently, requirements for the International Space Station (ISS) include achieving a 50% concentration of carbon dioxide (CO2) fire suppressant when extinguishing fires. This requirement is in accordance with NFPA 12, the governing standard for CO2 extinguishing systems, which requires concentrations of 50% for smoldering fires and 34% for flaming combustion. NFPA 12 was developed for fire suppression at ground conditions. This paper discusses combustion of materials in microgravity and evaluates CO2 fire suppressant concentration needed in microgravity and specifically for ISS environments. In a normal 20.9% oxygen environment on the ISS, the NFPA requirement should be more than adequate to extinguish flaming combustion in on-orbit microgravity conditions. For environments with initial oxygen concentrations higher than 25%, if a CO2 concentration less than 34% is desired, materials control should be exercised.

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.