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major incident on I-10 could receive up to 50 calls just letting us know traffic has stopped."
Veasco said the busy signal Hurley received probably came from his cellular provider, AirTouch Cellular. But it's also possible for callers placing a 911 call from home to receive a busy 'signal, she acknowledged.
"It would be if something like a fire in the Catalina Mountains was happening, or something loud and visible like a very large fire, and several houses all around it called," she said.
Louise Rebholz, a U S West spokeswoman, said that if more than about 30 residential Phone lines in one area call 911 at the same time, U S West will put what 'is called a "choke" on the calls allowing only as many calls through as there are lines free.
The 911 center also "chokes" calls, Velasco said.
The reason is to keep lines free for calls from other areas.
"If I let all the calls come in on the multiple reports of shots fired, I could be blocking another incident coming in from another
area," she said.
Velasco acknowledged the chokes could create a problem if another emergency popped up at the same time as the shots fired, and the whole area's 911 calls were blocked.
"It is a problem on how you balance. But if someone gets a busy signal, my advice is to hang ,up and call back," she said, stressling that most 911 calls are very brief and lines open up quickly.
She said it's rare for residential callers to get a 911 busy signal. "We've never had a 911 caller say they never got through and were unable to receive assistance," Velasco said.
The Pima County 911 system receives about 2,200 calls per day. Between 30 and 40 people work at the regional 911 center at any given time.
A 911 excise tax on telephone users' bills, regulated by the Arizona Corporation Commission, requires that U S West allow no more than one busy signal for every 100 calls placed to 911 during the busiest hour, Velasco said.
Patti Finley, a spokeswoman for Seattle based AirTouch Cellular, said it's also unusual for cellular callers to hear a busy signal on an emergency call unless it's because of interference with
the wireless signal, such as bad weather or a large building.
"It's very rare. We have very low blockage rates," she said.
The recent tornado in Salt Lake City was one situation that created such mass panic that the. cellular system gave out busy signals, Finley said.
Finley said in an emergency situation where, for example,, someone has a heart attack, the 911 line will almost certainly not' be busy for cellular users because such an incident would not gener- ate a high volume of calls.
I In other phone jams, I would' take a deep breath but know it's, probably busy because so many other people on the road have made the same call," she said.
Finley said the recording Hurley heard sounds more like a problem with the land phone fines.
"We would ask anyone to report any problems they encounter with 911. We really, want people to tell us about it and then we'll go back and research it the best we can," Velasco said. "We can have U S West go back and look at their records too."
Velasco said complaints about 911 in Tucson should be directed to the city's Communications Division at 791-3111.