Electrical current saving combined smoke and fire detector

Abstract

A fire detection system (10) includes a smoke detector (52) that measures smoke particle density indicative of smoldering fires and a CO.sub.2 detector (90) that measures CO.sub.2 concentration indicative of flaming fires. In a first operating current saving method, the smoke detector is operated at a normal PRF while the CO.sub.2 detector is operated at a very slow PRF. Smoke density measurements (14) produced by the smoke detector are compared with a set of tentative fire detection criteria (18, 20, 22, 14), and if met, the CO.sub.2 detector PRF is substantially increased to rapidly produce CO.sub.2 concentration measurements (26) that are compared to a set of conclusive fire detection criteria (30, 32, 36, 38). In a second operating current saving method, the CO.sub.2 detector is operated at a normal PRF while the smoke detector is operated at a zero PRF. CO.sub.2 concentration measurements produced by the CO.sub.2 detector are compared with a set of tentative fire detection criteria (30, 32, 36, 38), and if met, the smoke detector PRF is substantially increased to rapidly produce smoke density measurements that are compared to a set of conclusive fire detection criteria (18, 20, 22, 24). In a reliability improving operating method, electrical current draw and/or signal presence of the smoke and CO.sub.2 detectors are monitored to determine whether either detector has failed. If a failure is detected, fire detection criteria normally employed are changed to criteria optimized for the remaining detector.