Early stage fire sensing based on audible sound pressure spectra with multi-tone frequencies

An early stage fire-sensing technique based on audible sound pressure spectra with multi-tone frequencies in a security space is proposed. The sound pressure spectra, which are formed by a sound source in a confined security space, are measured from microphones installed within the space. Because the sound velocity depends on the air temperature, changes in the sound pressure spectra are induced by changes in the air temperature around the fire within the space. These changes in the sound pressure spectra can be used for the early stage of a fire-sensing system. The sound-pressure levels (SPLs) in multi-tone sound frequencies with and without local fire generation were measured and analyzed. Various case studies were conducted using a finite element method simulation in echoic spaces, and the experimental results from an echoic cube space and an office room were analyzed. The proposed method for monitoring the audible sound pressure spectra with multi-tone frequencies was shown to be a good solution for an early fire-sensing system within various types of security spaces.