As reported today by the Times Herald:
Firefighters from across the region will participate in a large scale fire exercise sponsored by Southeastern Pennsylvania Regional Task Force from 8 a.m. into the afternoon on Sunday, May 6.
Between 150 and 200 firefighters from 24 departments in Philadelphia, Bucks, Chester and Delaware counties will respond to a call for assistance from Montgomery County and participate in a series of seven drills throughout the day.
The most visible activity to motorists will be a simulated small airplane crash in a large parking garage off Fayette Street in Conshohocken, not far from the Fayette Street Bridge and the interchange with the Blue Route (I-476) and the Schuylkill Expressway (I-76).
The majority of the drills will occur at the Montgomery County Public Safety Training Campus, 1175 Conshohocken Road, Conshohocken, PA, 19428. They will include a live burn, simulated building explosion, large building search, mass decontamination and rescue scenarios.
So if you see some commotion on Sunday, it is just practice.