Bash for help

Bash for help
Apr 2nd 2009
From The Economist print edition


A new way to find trapped miners

HIGH technology is not always needed to solve a problem. Indeed, a proposed new system for finding miners trapped by an underground collapse is activated simply by hammering on an iron plate with a sledgehammer. Rescuers can be not only alerted by the banging but also guided precisely to the scene.
Sensitive listening equipment has long been used to try to hear people trapped underground. It is possible to detect seismic waves created by miners hitting rocks, say, but it can be difficult to distinguish these from other underground noises.
Now a more accurate method has been found. It involves bolting iron plates to the walls of tunnels at regular intervals and placing sledgehammers nearby. The idea is that, in the event of a collapse, survivors able to reach one of the plates would bash it to create vibrations that are detected by a string of geophones, standard devices used to measure seismic activity, placed on the surface along the line of the mine.
Gerard Schuster and his colleagues at the University of Utah first tested the idea in a tunnel that carries pipes three metres below the university campus. After positioning the plates, the researchers listened to the sound that each one made on being struck. Every sound was unique, in part because of small variations in the geology surrounding the plates. They used a computer monitoring the string of geophones to analyse the signals to see if they contained the seismic fingerprint of any of the underground plates. The system could detect if a plate was being hammered and which one, thus indicating the location of the person hitting it.