Browsing by Subject "PASS"
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Item Development of a sonar equation formalism for fireground acoustics(2013-08) Suits, Joelle; Wilson, Preston S.; Ezekoye, Ofodike A.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 providedItem Sound propagation in a compartment fire(2020-12-07) Abbasi, Mustafa Zafar; Wilson, Preston S.; Ezekoye, Ofodike A.; Hamilton, Mark F; Isakson, Marcia; Champlin, Craig AThe Personal Alert Safety System (PASS) is a device carried by firefighters to aid in rescue operations. The device relies on an audible alarm to help rescuers locate a downed firefighter. The fire creates thermal gradients, as well as randomly moving temperature gradients that affect sound propagation. This research is focused on understanding sound propagation in the presence of a fire. The problem was approached using experimental measurements, numerical modeling and analytical analysis. Results show that acoustic frequency response in a compartment fire is significantly changed when a fire is introduced. Low frequency modes increase in frequency and higher frequency modal structure weakens. Impulse responses show that acoustic energy arrives earlier, and later arrivals are shifted more than early arrivals. Numerical models confirm these results, and provide strong evidence that the effects are principally due to temperature variations. An analytic model is developed that predicts the modal frequency increase is a function of average temperature in the compartment.