COLLEGEVILLE, Pa. (AP) — Two of five bomb technicians injured in the detonation of an explosive device during a training exercise in Pennsylvania remained hospitalized a day after the accident, authorities said.

The FBI said three sheriff’s deputies from Montgomery County, a state trooper and an FBI special agent were injured in the accident at the SCI Phoenix prison in Skippack Township. The detonation occurred shortly before 10 a.m. Thursday. Some had “significant” injuries but there appeared to be no life-threatening injuries, officials said.

The FBI bomb technician was treated and released, federal authorities said, while the Montgomery County sheriff’s office said two of its deputies had also been treated and released. The third county sheriff’s deputy remained hospitalized Friday, and state police said the trooper also remained hospitalized.

The training session was being conducted by the FBI’s Philadelphia field office and those in attendance included representatives from several state, county and local law enforcement agencies. The cause of the accident remains under investigation. The FBI and the Pennsylvania state police are leading the investigation.

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