Fire Detection tradeoffs as a function of Vehicle Parameters

Fire survivability depends on the detection of and response to a fire and before it has produced a lethal environment in the vehicle. This is an interplay between the fire burning and growth rate; the vehicle size; the detection system design; the transport time to the detector (controlled by the level of mixing in the vehicle); and the rate at which the life support system filters the atmosphere, potentially removing the detected property. Given the large differences in critical vehicle parameters (volume, mixing rate and filtration rate) the detection approach that works for a large vehicle (the ISS) may not be the best choice for a smaller crew capsule. This paper examines the impact of vehicle size and environmental control and life support system parameters on the detectability of fires in comparison to the hazard they present. A lumped capacity model was developed that considers smoke, heat, and toxic product release rates in comparison to mixing and filtration rates in the vehicle. Recent work has examined the production rate of smoke and several hazardous species from overheated spacecraft polymers. These results are used as the input data set in the lumped capacity model in combination with the transport behavior of major toxic products released by overheating spacecraft materials to evaluate the necessary alarm thresholds to enable appropriate response to the fire hazard.