Researchers at the University of Texas at Austin are trying to answer an odd puzzle: why can't firefighters hear the super-loud emergency alarms they carry with them in emergency situations?
Firefighters, by the nature of their job, find themselves in life-threatening situations regularly. They carry a device called a Personal Alert Safety System, or PASS, just in case. The PASS is a motion-triggered alarm, attached to the harness that keeps their oxygen tank on. If the firefighter, and thus the PASS, doesn't move for 5 seconds straight, the alarm begins beeping loudly. If it's not addressed, it soon goes into alarm mode, screeching at about 95 decibels to alert other firefighters in the area. That's very loud, but firefighters report that it doesn't really work well, for the odd reason that they can't hear it in a burning building.
There are a few reasons for that: there's a lot of chaos in a burning building, there can be noises from elsewhere, it's dark and uncomfortable and frantic, and firefighters wear a lot of headgear. All of that is easy to understand as a reason why the alarms aren't audible. But there's another reason, too.
Sound travels faster in hot air than cold air. And burning buildings have pockets of very hot air and pockets of typical room-temperature air, and it's not predictable where those pockets will be. That means the sound is actually bending and distorting in there, so it can seem as if sound is coming from different places, making an alert chirp maybe not the best way to locate someone.
The researchers are working on a new version of PASS--perhaps merely making it louder would help, or maybe they need to change the pitch or tone of the sound, or maybe it's time to abandon sound altogether! What if GPS is a better way to locate people? So the team is trying first to figure out what the best option is for an alarm system, which will then go into the new device.
Read more over at KUT News.
95 dB isn't that loud. OSHA regulations are 85 over 8 hours. I think you're cleared at 95 for like 4 hours or something. And this is 1 meter away without hearing protection. In a noisy environment with gear on 95 just isn't loud.
"What if GPS is a better way to locate people?"
The GPS system has limitations. Perhaps military grade GPS would address some of them like accuracy. Commercial, publicly available GPS receivers are notoriously inaccurate in less that ideal conditions. Cloud cover, trees and electrical wires can weaken and distort the signals received from the satellites. I cannot imagine what being inside a burning building would do to them, but I am sure it won't make them more accurate.
The unit should signal non-action people outside the battle area. Then a team might be dispatched to rescue the officer. The firefighters have driving there in screaming trucks, fitted with gear, pumped up on the action, they can't be trusted to watch their life and fight a fire and listen for some signal. Maybe a variable signal would be useful but I doubt much louder would help. It is easy to tune out a single tone.
There are ways to get GPS accurate to a couple inches but they don't work in buildings where GPS itself is not reliable. Instead inertial positioning could be used. With sufficiently accurate clocks, gyroscopes and accelerometers you can determine your precise location with out any external signal. Have it transmit back to the firetruck and alerts could be sent out over radio. Longer term implementations could incorporated a heads up display and a blueprint you could track your position on a live map with the positions of other fire fighters. Add a 3d imager and even buildings with out blueprints could have one generated on the fly and incorporate data from each firefighter.