Many aspects of a firefighter’s work are not quite like the movies, and locating each other is one of them, according to a recent story from KUT News in Texas.  Visibility is poor or nonexistent in a real fire, so firefighters often have to rely on sound rather than vision.  A Personal Alert Safety System (PASS) is a device that emits a loud audible alarm if the wearer stops moving for more than a few seconds, allowing colleagues to come to the rescue.  Researchers at the University of Texas at Austin are working on ways to improve this system, which despite saving many lives doesn’t always work as well as it could.

For starters, an active fireground is a loud, noisy place, from things like sirens, power tools, engines, and the fire itself.  But beyond that, heat can do funny things to sound—hotter and colder parts of a room make sound travel faster or slower, and these changes in the speed of sound can actually bend sound waves that would otherwise travel in a straight line.  (Similar effects occur outdoors when the air temperature varies with height, such as being able to hear campers far away across a lake that cools the air.)  This heat refraction can wreak havoc with audibility and locating the source of a PASS beacon.  The current UT research will provide valuable insight into the sensory environment within a fire scene, and how compensation might be made for some of these acoustic challenges.