Expendable microphones may help locate building collapse survivors

Data gathered by Penn State engineers in a volunteer effort at the World Trade Center tragedy, suggests that simple, inexpensive microphones dropped into the rubble of a collapsed building may be able to aid search and rescue teams despite ground level noise.

Dr. Thomas B. Gabrielson, associate professor of acoustics and senior research associate at Penn State’s Applied Research Laboratory, says, “In conventional survivor searches, noise generating activities at the surface must be stopped while listening for survivors.”

However, the Penn State team found that the noise level in the interior voids of the rubble was about the same as that of a quiet residential neighborhood even though the noise level at the surface was much higher due to constant operation of three heavy lift cranes, air hammers, and dozens of rescuers workers.

“Our results suggest that if expendable microphones were dropped or thrown into the voids in a building collapse, the sounds from trapped survivors would be louder and the surrounding noise quieter so that acoustic search could be continued without interfering with other operations,” Gabrielson says.

Since the Penn State team made their measurements, they have developed small wireless microphones in hardened packages that can be thrown into areas too dangerous for people to enter.

The Penn State engineer adds, “Our goal is to provide a small, light, easy- to -use and expendable tool that doesn’t burden the rescuer with bulky, complicated equipment. ”

The researchers described their measurements and findings in the current issue (January) of the Journal of the Acoustical Society of America. The authors are Gabrielson, Matthew Poese, doctoral candidate in acoustics, and Dr. Anthony Atchley, professor of acoustics and head of the Penn State Acoustics Program.

The Penn State team listened to and recorded signals Sept. 18 at the edge of the rubble pile on the northwest corner of the heavily damaged Bankers Trust building.

The researchers write, “These results support the strategy of lowering microphones into collapsed structures in addition to listening for survivor signals from the surface. Placing the microphone in voids in the collapsed structure reduces much of the surface-produced airborne noise.”

The Office of Naval Research has provided continuing support for the development of acoustic systems at Penn State’s Applied Research Laboratory (ARL) and the resulting ARL infrastructure made the team’s acoustic survivor search effort possible.