Photoacoustic Compound Fire Alarm System for Detecting Particles and Carbon Monoxide in Smoke

In view of the high sensitivity and high selectivity of photoacoustic technology, a compound fire alarm system used for detecting smoke particles and carbon monoxide was designed on the basis of the photoacoustic spectrometry principle. The system uses an infrared laser with a central wavelength of 1579 nm as the light source, adopts wavelength modulation technology to modulate the continuous light source, and moves the inspection frequency to high frequency with lower noise by integrating harmonic detection technology, thus realizing a measurement of the photoacoustic signal. Concurrently, the system obtains the CO concentration and extinction coefficient of smoke particles via inversion by using the measured scattered light intensity data combined with a certain algorithm. A test was carried out on the system by using three small-scale experiments, namely, cotton rope smoldering fire, polyurethane foam fire and sandalwood smoldering fire. The results show that the CO gas concentrations and extinction coefficient of smoke particles produced by these three experiments are well detected. The CO detection limit of the system was 2.98 ppm. The test results also show that pure powder (used for simulating particles) or pure CO gas will not trigger the system alarm, so unnecessary alarms caused by traditional fire detectors can be avoided and the reliability of the fire alarm can be improved.