They have been among the most striking images to come from the post-earthquake rubble of Mexico City: men, women, and babies emerging from underneath tons of wreckage. The scenes have highlighted some little-publicized technologies first designed to help rescue trapped miners. From supersensitive microphones and seismic detectors that hear faraway heartbeats, to special low-light remote TV cameras that enable rescuers to peer into darkened crevices, these technologies have found little use so far in mine-rescue work. This is because so far, there have been no opportunities to use them in the United States.
So many experts here have been monitoring their use in Mexico City with particular interest.
Matthew McCullough, director of the Office of Technical Support in the US Department of Labor's Mine Safety and Health Administration, terms the use to which these devices have been put in Mexico ``miraculous.''
``I think it has been a remarkable test not only of the equipment but of the people down there -- heroes every one of them,'' he said.
Mr. McCullough oversees the Mine Emergency Headquarters in Aliquippa, Pa., where a response team is on call 24 hours a day to respond to mine emergencies. The team, Westinghouse employees contracted by the federal government, also develops the sorts of devices being used by an interagency US team in Mexico City. The 10-member team includes personnel from the US Department of Interior's Bureau of Mine and Office of Surface Mines, as well as the Mine Safety and Health Administration. The team is employ ing technology introduced some 15 years ago, largely at the Mine Emergency Headquarters.
One device, called a geophone, is an extremely senstive dectector that picks up minute vibrations in the earth's surface. The geophone can detect vibrations as small as a few millionths of an inch, says John Murphy, research director of the Bureau of Mines' Pittsburgh Research Center. That is sensitive enough, he says, to pick out the tapping of a miner's helmet 1,200 feet below the surface.
The drawback to the geophone, says Mr. Murphy, is that it picks up vibrations from passing cars, trucks, and people hundreds of yards away as easily as it picks up the tapping of a trapped miner or earthquake victim.
A particular challenge for technicians has been the development of computers that can sift out the background ``noise'' from the sounds investigators are searching for.
Remote TV cameras have allowed rescuers in Mexico City the chance to peer into otherwise unreachable areas of a collapsed structure. The cameras, mounted on the end of a long, flexible pole, carry their own light source.