The Combustibility of Materials in Oxygen-Helium and Oxygen-Nitrogen Atmospheres

Abstract

The energy required for ignition of various materials and the rate at which flames spread over the surface after ignition were determined in oxygen- nitrogen and oxygen-helium mixtures in order to assess the fire hazards associated with proposed space cabin atmospheres. It was found that flames spread more rapidly in oxygen-helium mixtures than in comparable oxygen-nitrogen mixtures. The experimental data correlated well with the specific heats of the gas mixtures per mole of oxygen, indicating that the flame temperature is the dominant factor in determining flame spread rates. A theoretical model of flame spread was developed. Slightly more energy was required to ignite materials in oxygen-helium than in oxygen-nitrogen mixtures. However, the difference was small enough so as not to reduce significantly the fire hazards, especially since the flames spread more rapidly once the material was ignited. It was concluded that fire hazards are greater in oxygen-helium atmospheres than in oxygen-nitrogen atmospheres.