Final alarm: Philadelphia Fire Department sounds memorial bell for firefighters who died in 9/11

PHILADELPHIA - A solemn tradition holds an even deeper meaning today as the Philadelphia Fire Department rings the bell for those whose service ended after the terror attacks on September 11.

Nineteen members of Philadelphia's heavy fire rescue were sent to New York City, offering assistance in the aftermath of 9/11.

To honor the fallen firefighters, as well as citizens who died in the attacks, the Philadelphia Fire Department sounds a memorial bell.

Three bells ring three times in a row to signify that a firefighter has ended their shift, and performed their last alarm.

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The ringing of the bell is part of a 9/11 memorial service at Betsy Ross' house that features guest speakers and a memorial to those who have fallen in the line of duty.