The analysis of sound wave scattering using a firefighter’s Personal Alert Safety System signal propagating through a localized region of fire

Abstract

Firefighting is quite clearly a dangerous and risk-filled job. To combat these dangers and risks, firefighters wear a (National Fire Protection Agency, NFPA 2007 edition of the 1982 standard) Personal Alert Safety System (PASS) that will sound a loud alarm if it detects (for example) the lack of movement of a firefighter. However, firefighters have experienced difficulty locating the source of these alarm chirps (95 dBA around 3 kHz) in a burning building. The project goal is to determine the effect of pockets of varying temperatures of air in a burning building on the sound waves produced by a PASS device. Sound scattering experiments performed with a vertical heated air circular jet plume (anechoic chamber) and with a wood fire plume from burning cylindrical containers (Anne Arundel Fire Department’s Training Facility) suggest that from Snell’s Law, sound rays refract around such pockets of warmer air surrounded by less warmer ambient air due to changes in the sound speed with temperature through the medium. Real-time and spectral measurements of 2.7 kHz CW sound scattering (using a microphone) exhibit some attenuation and considerable amplitude and frequency modulation. This research may suggest future experiments and effective modifications of the current PASS system.