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.