Design and Test of a Fire Detection System for a Microgravity Environment

Fire detection in a microgravity environment produces a number of concerns. On Earth, smoke particles generated by a fire are often used to trigger an alarm signal. In space, without the thermal buoyancy effects produced by gravity, smoke particle movement is more random, making its detection more difficult. This problem presents itself to the module outfitters who are designing a fire detection system for the Space Station. The volumes behind the racks, referred to as exo-rack areas, are particularly difficult to monitor because they are hidden from view by closeout panels. Still, the exo-rack areas must be monitored because they contain wiring and electrical equipment that presents a potential fire hazard. A strategy for detecting fires in the Space Station exo-rack area has been developed by the McDonnell Douglas Environmental Control and Life Support Systems (ECLSS) team. The system uses piccolo tubes to collect samples of air from the exo-rack areas in the node. The sampled air is drawn past a smoke detector, which uses scattered laser light to detect smoke particles. A prototype of this system was installed in a mockup of the Space Station node for development testing. Smoke samples were passed into various compartments within the node exo-rack and the response time and detector signal strength were measured. Although the test was subject to the effects of gravity, unique test techniques allowed valuable information on the performance of the system to be gathered and inherent limitations to be identified. This paper discusses the planning, procedure, and results of this development test. Particular attention is paid to the methodology used for acquiring repeatable data and the parameters that drive fire detection system performance.