July 21, 2005 NASA researchers have successfully tested a new generation of fire detectors that could significantly reduce the rate of false alarms in the cargo and baggage compartments of commercial airliners.
The new sensor-based system was developed at NASA's Glenn Research Center (GRC), Cleveland. It reads a more complete fire signature, and it is so sensitive it may reduce false alarm rates to zero.
Most detectors sense smoke particles. They can be fooled by dust and other tiny airborne particles found in non-passenger an aircraft compartment, which leads to false alarms. The team at GRC used MicroElectroMechanical Systems (MEMS) expertise to come up with a new multi-sensor approach.
"We looked for increased concentrations of combustion gases along with the smoke," said Gary Hunter, a Sensors and Electronics Branch aerospace engineer. "The multi-sensor package compares various gas concentrations and smoke particle sizes to those values characteristic of an actual fire. The result is a system that works to effectively recognize the presence of fire while screening out false alarms."
The MEMS sensor system includes miniaturized carbon monoxide and carbon dioxide sensors, a smoke particle detector and integrated software. These compact arrays can be placed in multiple locations throughout the aircraft's cargo and baggage compartments. The on-board processor evaluates the response of the complete sensor system and indicates whether there is a fire.
Fire alarms signal pilots to initiate emergency procedures. A Federal Aviation Administration (FAA) survey of airline maintenance reports has estimated that 100-200 false alarms occur for every actual fire. In-flight fires are rare, but there is no way for flight crews to verify sensor readings to know for sure a fire has started in a remote compartment. So every alarm must be taken as seriously. This means using extinguishing equipment, declaring emergency priority over other air traffic and, landing as soon as possible.
GRC researchers teamed with colleagues from Case Western Reserve University, Cleveland; Ohio State University, Columbus; and Makel Engineering, Inc., Chico, Calif.; in collaboration with the FAA.
Tests conducted at the FAA Cargo Compartment Fire Testing Facility in Atlantic City, N.J., successfully demonstrated the miniaturized, combined chemical and particle sensors approach. NASA's multi-sensor package had a zero false alarm rate when exposed to conditions that would normally cause cargo compartment detectors to false alarm. Further testing alongside conventional smoke detectors in the FAA's Boeing 707 under-floor cargo bay showed the system detected fire as well as conventional smoke detectors.
Before the new system can be installed on airplanes, the sensors, software packaging and interface, long-term durability and drift effects need to be improved and certified by the FAA. NASA's Aviation Safety and Security Program sponsored the research as part of a joint NASA-FAA program. Industrial Research and Development Magazine recognized the effort as one of 100 best technical research and development achievements of the year.
False alarms are also a concern in International Space Station operations and during space exploration missions, so NASA is sharing this research with spacecraft developers.
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