PHILADELPHIA — The FBI and Pennsylvania State Police are investigating a Thursday morning explosion that took place during a law enforcement training exercise at SCI Phoenix prison in Skippack Township, Montgomery County. The FBI didn’t immediately say how many were injured when a live training device unexpectedly detonated but bomb technicians from the Montgomery County Sheriff’s Office, Pennsylvania State Police and FBI Philadelphia were among those sent to area hospitals. The number of those injured and their conditions were not immediately made known by federal investigators, but a Pennsyl…