What is happening at the SPS Technologies aerospace facility?

A large fire broke out at SPS Technologies, an aerospace manufacturing facility north of Philadelphia, around 9:30 PM local time. Witnesses reported explosions and visible flames inside the warehouse. Schools have been closed and residents ordered to shelter in place as officials monitor air and water quality. Firefighters are working to bring the fire under control. Fortunately, all employees are accounted for and no injuries have been reported.