In some of the city's most heavily populated neighborhoods - Center City, Grays Ferry and University City - cell-phone signals have blocked radio communication for firefighters at the scene of fires, department officials confirm.
No firefighter has been injured as a result of radio problems, but union representatives for firefighters say the risks are too great.
A blocked radio signal, which makes a "bonking" sound, "is the sound of death," said David Kearney, a Philadelphia paramedic and officer for Local 22 of the International Association of Fire Fighters.
Interference from cell phones on the 800-megahertz (MHz) band of the radio-frequency spectrum is a problem confronting firefighters, police, and emergency medical workers across the country.
Fire and police units in Philadelphia suburbs such as Upper Merion and East Norriton have complained of cell-phone interference. In New Jersey, state police have received reports of interruptions in every part of the state.
Last month, the Federal Communications Commission proposed moving all cell-phone carriers to one end of the 800-MHz band and all public-safety users to the other.
But any agreement would need the approval of Nextel Communications Inc. of Reston, Va., the largest commercial user of frequencies in the 800-MHz range. The plan calls for Nextel to acquire a new band of spectrum worth $4.8 billion. In return, the company would have to pay to reconfigure public-safety signals in the 800-MHz range.
Nextel is reviewing the FCC proposal, said Leigh Horner, a company spokeswoman.
Any plan, however, would take up to three years to put in place. In the meantime, Philadelphia firefighters have filed a steady number of complaints about interference.
At a house fire in Grays Ferry on June 27, for example, a fire chief who could not get through to crews via radio had to resort to yelling commands to firefighters inside, eyewitnesses said.
Lloyd Ayers, the city's acting fire commissioner, said his department was aware of the interference problems and was working with cell-phone carriers to find solutions.
"It's a big concern," Ayers said. "We're doing what we can to assure we have a remedy for this."
The Fire Department's Motorola 800-MHz radio system was installed in October 2002, replacing an outdated 150-MHz network. Both the Fire and Police Departments are hooked up to the Motorola system, which cost the city $54 million.
Cell-phone interference was not a problem with the old system because there were no cell-phone carriers operating on the 150-MHz band. But with the 800-MHz band, cell-phone signals are bumping up against public-safety channels.
City and fire officials say Nextel and Cingular Wireless are the suspected culprits. The city has hired technical experts to verify signal interference and to pinpoint which cell-phone carrier could be to blame.
Spokeswomen for Cingular and Nextel said their companies were cooperating with city officials.
Part of the problem is that city officials do not know where cell-phone towers are located, and companies hold that information close to the vest.
As a result, a firefighter making a call at an 850-MHz frequency might unknowingly be standing under a cell-phone antenna transmitting at 851 MHz. One signal could block the other.
Temporary fixes - such as adjusting frequencies or realigning towers - are neither reliable nor permanent, said Robert Gurss, director of legal affairs for the Association of Public-Safety Communications Officials.
"Even if you know how to fix it, you can't go through that process every time you have an interference problem," Gurss said. "It's a dangerous approach. You're chasing problems after they occur, and one of these days someone's going to die as a result."
Kearney, of the firefighters' union, said cell-phone interference is just one of many problems that first responders have found with the city's new radio system.