Development of a sonar equation formalism for fireground acoustics

Firefighters wear a plethora of personal protective equipment (PPE) in- cluding a Personal Alert Safety System (PASS) device. This device produces an audible alarm signal when it senses a lack of movement to help rescue teams detect and find firefighters who have become incapacitated on the fireground. Although this alarm works the majority of the time, there are instances where it has failed to be detected or found. Using a passive sonar approach, this study begins to provide a scientific background to improve the signal. The construct of the passive sonar equation helps to define a signal-to-noise ra- tio with information about the environment, source and receiver. This work presents studies of the noise level of the environment (NL), source level (SL) of the PASS device, and detection threshold of the receiver (DT) on the fire scene. To study NL and SL, equipment used by firefighters was recorded and analyzed for the sound pressure level, frequency content, and directionality compared to the PASS alarm. The NL on a fire scene has been found to be broadband, high intensity noise. The loudest piece of equipment was found to be a chainsaw and the quietest to be a pumper truck. The DT involves the ability of firefighters to detect and classify the PASS signal. Physical acous- tic experiments, using an acoustic manikin, show that PPE gear affects the sound reaching the ear by reducing the average received level and introducing peaks and nulls in head related transfer functions. In audiological tests on normal-hearing human subjects, this manifested itself by increasing the sound pressure level required to detect the PASS alarm while wearing PPE gear. Recommendations based on these findings are provided