Photoacoustic Method to Detect CO and Soot Particles Generated by Fire

This paper presents a method to detect both fire produced gas and soot particles in the environmental air. CO gas and soot particles in fire smoke can both produce photoacoustic (PA) signal due to their light absorption. In this method, different light sources were used to excite PA signal from the two absorbers. CO gas has narrow absorption lines, while soot absorbs light in wide range of infrared spectrum. Here an open PA cell was used to allow the gas and soot particles to enter it by diffusion. When the investigated mixture in the PA cell is alternately illuminated by modulated laser beams at CO absorption line and another reference spectrum, it will produce different PA signals. They are devised to represent separately the summation of gas and soot absorption and the soot absorption. By establishing a relationship between the signals, the gas induced and soot induced photoacoustic signal can be achieved individually. Then, their concentration can be calculated.