NIST worker tests radio in New York City subway station

Can emergency radio gear get clear in tunnels, skyscrapers?

It came as no surprise that radio equipment used by firefighters did not always work very well in subway tunnels and skyscrapers during recent trials, but the results of the government tests could help set new technical standards for safety equipment used by emergency responders.

The tests, conducted by the National Institute of Standards and Technology, were funded by the Homeland Security Department to measure performance in urban environments of RF Personal Alert Safety Systems (RF PASS) used by firefighters. They were carried out in New York City’s subway system and the Empire State Building in late 2011.

“The range of success with one of the point-to-point systems during the RF PASS systems testing verified that good, but not complete, coverage was indeed possible,” the NIST report concluded.

But under current standards for the devices, performance can be hampered in complex environments that interfere with the radio signals. The purpose of the test was to provide data needed for further standards development, said William Young, a NIST electrical engineer and an author of the report.

“It was to support the development of test methods on a broader scale,” Young said. “We wanted to make sure that the tests represent the real world conditions that they are going to be working in.”

The tests were part of a multiyear effort to support development of performance metrics and test methods for the equipment. Earlier NIST work already has been incorporated into standards adopted by the National Fire Protection Association to allow the certification of RF-based safety equipment, such as PASS beacons. These are mobile devices worn by firefighters that can let a local base station monitor the firefighter’s activity. They can send alerts if the firefighter is in trouble and can receive evacuation signals from the base station.

But the current standards set a relatively low bar for operation in non-challenging environments. To help raise that bar, NIST conducted tests with four commercial RF PASS models working in three different frequency bands.

“It turned out pretty much as expected,” Young said. “They communicate to the range they were anticipated to from earlier tests.”

But when moved underground or into large multi-story buildings the signals were less reliable. Multilevel subways proved a bigger challenge than the skyscraper, with devices generally not communicating beyond the initial entrance level of the subway. This suggests that repeater systems to relay signals probably would be needed to communicate with an outside command post.

Although the current report focuses on RF PASS equipment, the methodology and results could be extended to other types of radio equipment used by emergency responders, the report said.

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