  The Personal Alert Safety System (PASS) is an alarm signal device carried by
firefighters to help rescuers locate and extricate downed firefighters. A fire
creates temperature gradients and inhomogeneous time-varying temperature,
density, and flow fields that modify the acoustic properties of a room. To
understand the effect of the fire on an alarm signal, experimental measurements
of head-related transfer functions (HRTF) in a room with fire are presented in
time and frequency domains. The results show that low frequency (<1000 Hz)
modes in the HRTF increase in frequency and higher frequency modal structure
weakens and becomes unstable in time. In the time domain, the time difference
of arrival between the ears changes and becomes unstable over time. Both these
effects could impact alarm signal detection and localization. Received level of
narrowband tones is presented that shows the fire makes the received level of a
source vary by >10 dB. All these effects could impact the detection and
localization of the PASS alarm, and life safety consequences.
