Low-pressure flame spread limits of fire resistant fabrics

Abstract

Future space missions may require spacecraft cabin environments different than those used in the International Space Station. These cabin environments may even vary between exploration vehicles depending on mission purpose and duration, among other factors. Environmental variables such as flow velocity, oxygen concentration, ambient pressure, micro or partial-gravity, orientation, presence of an external radiant flux, etc. may increase or decrease the material flammability for any particular set of environmental conditions. The goal of the current work is to study the effect of oxygen concentration, ambient pressure and sample orientation in the limiting conditions for flame spread over Nomex HT90-40. Experiments were conducted inside a 105 liter pressure chamber with ambient pressures ranging from 13 to 100 kPa and oxygen concentrations ranging from 21% to 75%. Flame and no-flame spread boundaries are reported in terms of ambient pressure and oxygen concentration for both concurrent and opposed flame spread conditions. The criteria used to define the flame and no-flame spread boundary was the measured maximum oxygen concentration for which the flame propagated beyond the influence of the igniter. Results show that the minimum oxygen concentration for flame spread increases as ambient pressure decreases, with more significant increases observed at low ambient pressures. In addition, the results from the present work explore the relationships that exists between sample orientation, flame spread configuration and environmental variables such as ambient pressure and oxygen concentration.