Towards Application of SMOX Sensors for a Pre-Ignition Fire Detection System

Detection of fire hazards prior to ignition would greatly enhance fire safety, especially in human spaceflight where evacuation options are very limited and residual products of smoke and fire suppression are difficult to remove. Previous work has demonstrated the ability of semiconducting metal oxide gas sensors to detect the outgassing of heated polymers (PMMA, PVC, and ePTFE). In this work, the materials Nomex™, Kapton™, PDMS, and PMMA were investigated with respect to the onset of the sensor signal during semi-random incremental heating steps in a 0.8 x 0.8 x 1.6 m glass chamber. The data is further evaluated using Ridge Regression and the quality of temperature prediction quantified by different error metrics. By operating a second sensor in a predefined modulated operating temperature, the information gain was greatly increased, improving the prediction and decreasing the error. To test in a less controlled and therefore more challenging environment, experiments were conducted in a second metallic test chamber. The setup introduces laminar flow and allows the test materials to be heated above their operating temperatures. It was found that in all tests the overheating event could be detected within 4-7 minutes response time. The successful detection of overheating in both closed mode (with exhaust remaining in the vessel) and open mode (where ‘fresh’ air is introduced, simulating air purification by an ideal air scrubber) demonstrates the overall suitability of the sensor system for the intended application in spacecraft environments.