When firefighters are overcome by the heat or smoke of a fire and become disoriented or trapped in a structure, it is crucial that there is a reliable means to alert other fireground personnel to their need for assistance. Personal Alert Safety System (PASS) devices are designed to signal for aid using audible signal technology. Normal operation is for the PASS devices to activate a 95-decibel multiple-frequency alarm signal if the device is stationary for a specific period of time or is manually activated. However, despite its widespread use throughout the fire service and on-going enhancements in recent years, certain problems still exist with audible PASS technology. Foremost among these problems is that nationally recognized standards currently do not specify a unique PASS alarm signal, and this has resulted in multiple different PASS alarms being used in the field. In this work, we present results that seek to establish a scientific basis for an optimum PASS alarm signal for use throughout the U.S fire service. We present typical sounds recorded from firefighter operations. We discuss how these sounds interfere with typical PASS signals both in compartments with and without fire. Using experimental and computational results for sound propagation within compartments with fire and thermal stratification, we show how acoustic signals are modified and affected in the gas phase by the fire evolution. Additionally, the effects of thermal degradation of typical building materials such as gypsum board is discussed in terms of the impacts on sound propagation.

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