Adjusting For The Bending Sound
CAN YOU HEAR THE P.A.S.S. ALARM sounding? Can you tell where it's coming from? The answer to both of those questions is, "Maybe, and maybe not."
What began as a quest for a standardized sound to identify a PASS alarm grew into a discovery of "bending" sound waves that distort alarm signals in confined fire spaces. Thus a project became a dual-purpose project at the University of Texas at Austin where a research team is working to standardize a universally-recognized sound for the alarms.
Joelle Suits is a graduate student at UT and is studying fireground acoustics. A report from public radio station KUT-FM fills us in on what's going on there. They tell us in part:
"There were cases where firefighters would hear the device outside the house," Suits said. "But once they got inside, they couldn’t hear it or couldn’t find it and they’re not entirely sure why."
In a real fire, he says, a firefighter probably can’t see a thing. "They are in pitch black conditions and they have to rely on these other senses – particularly auditory in this case – to try to determine what’s going on."
But hearing what’s going on isn’t so easy. There (are) sirens, water pumps, radio traffic, fans pushing smoke out of the building, saws – sometimes car alarms and smoke detectors. Plus, firefighters are wearing a helmet and protection around their face and ears – muffling the sounds around them.
And then things get weird.
The air is hotter or cooler in different places around a room that’s on fire. "And sound moves faster in hotter temperatures than it does in cooler temperatures," says Joelle Suits. "Which can distort and actually bend sound."
Which can make it sound like a sound is coming from somewhere completely different than the actual source. Which is a problem when you’re using that sound to locate a colleague in peril.
Suits acknowledges that GPS transponders and homing beacons are being adapted to some degree of efficiency to PASS systems, but they are far from reliable enough to become the standard for the technology. While the standards were upgraded six years ago to increase the device's resistance to heat and water, one of the biggest problems is identifying the sound of the alarm. Different manufacturers all have their own noise for it and none are distinctive enough to be recognizable for what it is.
The UT team is working on a) a unique sound that will not be confused with other typical fireground noises, and b) a sound that has the pitch and frequency range that will penetrate the fire environment and be heard, and located, from inside the fire building.
They are hoping to have their proposed guidelines ready sometime next year. The next generation of PASS alarms just might sound like this:
Read the entire report from KUT-FM HERE.
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