Demolition tests radio signals

Researchers at the National Institute of Standards and Technology are hoping to develop better emergency communications by testing how radio signals fared before, during and after the Dec. 18 implosion of the Washington Convention Center in Washington, D.C.

The purpose is to determine how to improve communications in shielded or complex environments, such as basements or elevator shafts, and detect signals through building rubble.

Agency officials placed 25 battery-operated radio transmitters — which emit signals close to frequency bands used by emergency responders — at various locations at the convention center prior to the demolition. NIST researchers were to monitor and map signal strength throughout the entire process and study "the various schemes for detecting signals by searching with directional antennas and by connecting detectors to metal debris found within the rubble of the building," according to a press release on NIST's Web site.

It is the third time the agency has performed such tests at structures that were being imploded. The first time was in January at the 13-story Fischer Public Housing Project in New Orleans. In March, the agency performed tests at Philadelphia's Veterans Stadium.

"We're trying to understand the whole radio propagation process in these huge buildings both before and after a collapse," Chris Holloway, a NIST researcher who heads the experiments, said in the press release. "We're specifically looking at very large buildings because that's where you're likely to have communications problems and large numbers of people involved in an emergency situation."

After the Sept. 11, 2001, terrorist attacks, rescuers at the World Trade Center worked with several wireless phone companies to develop ways to locate trapped people whose wireless phones were possibly operating and emitting signals through the rubble. Reports about the attacks documented the lack of voice radio communications among New York City firefighters and police, which resulted in hundreds of first responder deaths. Communications interoperability, including voice, video and data, has since become a national issue.

Public and private researchers also have been testing peer-to-peer, self-organizing networks in which personal digital assistants, handheld computers or other devices act as both receivers and transmitters, thereby creating a communications mesh. Signals can hop from one device to another. If one part of the network goes down, the signals can still bounce to another device.

From these and other tests, NIST officials hope to develop reliable, cost-effective tools that can be retrofitted in existing radio systems to help first responders locate and communicate with one another and with individuals trapped inside a collapsed building.

"For example, using software that turns sounds into visual images, first responders may be able to receive and see simple patterns — like Morse code — from a survivor repeatedly turning a radio or phone on and off, in cases where the signal was too weak to receive audible voice messages," according to the press release.

The project is being funded in part by the Homeland Security Department and the Justice Department's Community Oriented Policing Services Office.