PASS Audibility Project
Analysis of Fireground Sound
Using the passive sonar equation approach, the signal level (SL) and noise level (NL) are critical components necessary to determine whether firefighters are able to determine and localize a PASS signal. The noise level includes every sound that is not PASS on the fireground, including chain saws, circular saws, ventilation fans, water pumps, sirens, etc. We explored the levels of these sounds on the fireground to determine an accurate noise level for our analysis. The plots below show the sound level of the equipment relative to the PASS signal in 1/3-octave bands.
Saws (Circular, Chain)
1/3-Octave Band Analysis of Saws at 0 Deg.
1/3-Octave Band Analysis of Saws at 90 Deg.
1/3-Octave Band Analysis of Saws at 180 Deg.
1/3-Octave Band Analysis of Saws at 270 Deg.
Engine Noise
1/3-Octave Analysis of Engine at 0 Deg.
1/3-Octave Analysis of Engine at 90 Deg.
1/3-Octave Analysis of Engine at 180 Deg.
1/3-Octave Analysis of Engine at 270 Deg.
Positive Pressure Ventilation (PPV) Fans
1/3-Octave Band Analysis of PPV Fans at 0 Deg.
1/3-Octave Band Analysis of PPV Fans at 90 Deg.
1/3-Octave Band Analysis of PPV Fans at 180 Deg.
1/3-Octave Band Analysis of PPV Fans at 270 Deg.
CONCLUSIONS
The PASS device recorded in this study met the minimum requirement set by NFPA 1982-2007. However, most of the equipment recorded is above that level. The loudest piece of equipment recorded, a chainsaw, was 11.6 dB above the PASS device in overall SPL. This is an SNR of -11.6 dB for a listener equidistant from both sources. The piece of equipment with the lowest sound pressure level is the engine at 88.47 dB. This is an SNR of +10.43 dB. A larger SNR means a higher probability and a greater range of detection.
Another point of interest is that most of the noise on the fireground is broadband noise containing many frequencies. The PASS device is a narrow band source at 3150 Hz. In this band, the previously mentioned chainsaw is only 4 dB above the PASS device.
