Fundamentals of Fire Suppression in Reduced Gravity Environments

This paper discusses the unique aspects of fire suppression in reduced (micro- and Lunar/martian) gravity environments. It builds on a trade study conducted by the Fire Prevention Detection and Suppression group at the NASA Glenn Research Center that examined the efficacy of fire suppressants in reduced gravity. The first part of the present paper reviews the differences in flame characteristics between terrestrial and extraterrestrial fires and how these characteristics change the action of a fire suppressant. Special emphasis is placed on enriched oxygen ambient environments, a condition that will routinely exist on future spacecraft and extraterrestrial habitats. The most important difference between normal gravity and reduced gravity fires is the increase in the minimum suppressant concentration (for gaseous agents in a total flooding application) required to extinguish a fire in reduced gravity compared to normal gravity. The impact of this observation is that suppressant system design guidelines based on terrestrial standards will either not be adequate or will not offer the same factor of safety in reduced gravity. The paper discussion focusses on inert gas (most suitable for total flooding applications) and water mist systems (suitable for total flooding and streaming applications), with some results for chemically active systems (e.g. Halon 1301) included for reference. Finally, the paper presents recommendations on proposed tests and standards to evaluate candidate suppressant technologies.