Microgravity Flame Spread over Non-Charring Materials in Exploration Atmospheres: Pressure, Oxygen, and Velocity Effects on Concurrent Flame Spread

The objective of this work is to determine the dependence of microgravity flame spread on ambient pressure, oxygen concentration, and velocity typical in exploration spacecraft and habitats. Since it is impractical to test a wide range of materials, these characteristics are being determined for major classes of materials. In the current work, a non-charring thin fuel (25-micron thick Shinkolite™ast;) was tested in microgravity to compare with previous results with a charring thin fuel. Microgravity concurrent flame spread tests were performed in a low-speed flow tunnel to simulate spacecraft ventilation flows (7–31 cm/s). The tunnel atmosphere pressure and oxygen concentration was varied over a wide range (21–85% O₂, 5–16 psia).

Flame spread rate was measured to develop correlations that capture the effects of flow velocity, oxygen concentration, and pressure on the spread rate. The non-charring fuel exhibited a linear dependence on flow, similar to the charring fuel. However, the non-charring fuel had a weaker dependence on oxygen (square root versus linear for the charring fuel). The non-charring fuel was independent of pressure, unlike the square root dependence on pressure found for the charring fuel. These results demonstrate that the effect of spacecraft atmosphere on concurrent flame spread depends on the class of material, so it would be prudent to develop fire safety protocols based on the most hazardous of the different correlations. The stronger dependence on oxygen concentration for both charring and non-charring fuels shows that the lower ambient pressure planned for exploration spacecraft and habitats does not offset the increased hazard of elevated oxygen.