Ray tracing and finite element modeling of sound propagation in a compartment fire.

A compartment fire (a fire in a room or building) creates temperature gradients and inhomogeneous time-varying temperature, density, and flow fields. This work compared experimental measurements of the room acoustic impulse/frequency response in a room with a fire to numerically modeled responses. The fire is modeled using a Fire Dynamics Simulator (FDS). Acoustic modeling was performed using the temperature field computed by FDS. Room acoustics were modeled using two-dimensional ray and finite element modeling. A three-dimensional model was used to simulate an open flame. COMSOLTM Multiphysics was used for finite element acoustic modeling and BELLHOPTM for ray trace acoustics modeling. The results show that the fire causes wave-fronts to arrive earlier (due to the higher sound speed) and with more variation in the delay times (due to the sound speed perturbations). The resonance frequencies of low-frequency modes were shifted upwards. Model results are compared with data and show good agreement in observed trends.

Head-related transfer function measurements in a compartment fire.

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 of these effects could impact alarm signal detection and localization. The receive level of narrowband tones is presented that shows that the fire makes the receive level of a source vary by > 10 dB. All of these effects could impact the detection and localization of the PASS alarm and have life safety consequences.

Change in acoustic impulse response of a room due to a fire.

A room fire creates temperature gradients and inhomogeneous time varying temperature, density, and flow fields. Experimental measurements of the room acoustic impulse/frequency response are presented and compared with a ray traced model. The results show that the fire causes wave-fronts to arrive earlier (due to the higher sound speed) and with more variation in the delay times (due to the sound speed perturbations). The frequency response shows that the modes are shifted up in frequency and high frequency (>2500 Hz) modes are significantly attenuated. Model results are compared with data and show good agreement in observed trends.

A model for assessing ignition, flame spread, and burn hazard potential of a multilayered jacket.

An analysis is presented of ignition, flame spread, and skin burn associated with the ignition and burning of a multilayered jacket. The important physical processes can all be detailed based on simple thermophysical modeling. The ignition process associated with proximity to a radiant heat source is analyzed to see how a change in external (outer) fabric could have diminished the likelihood of ignition. Once the composite jacket has been ignited, the flame spread process is responsible for the heat transfer to the skin that causes the burn. We analyze the effects of the jacket innermost material on flame spread and on possible burn damage. We show how available thermophysical property data can be used to estimate the effect of inner layer material on burn event duration. Finally, given best-available data on the heat transfer rates between a burning inner layer and skin, we examine the kinetics of skin burn damage to determine the most likely injury that would result.