IRVINE — Sixteen Orange County sheriff’s SWAT deputies were injured in an explosion during a  training exercise Wednesday at an FBI facility in Irvine, but the injuries were all considered relatively minor.

The most serious injury was to the leg of one man who will require surgery but is not in life-threatening condition, authorities said.

Orange County Fire Authority paramedics were dispatched at 12:54 p.m. to the training facility at Irvine Boulevard and Magazine Road, according to OCFA Capt. Sean Doran.

“A training incident that occurred today at the FBI’s training facility in Irvine with law enforcement partners resulted in some injuries and is under investigation,” FBI spokeswoman Laura Eimiller said.

During the training exercise a device exploded indoors.

One deputy suffered a leg injury and another to the back, but they were considered superficial wounds, said Orange County Sheriff’s Sgt. Frank Gonzalez.

Thirteen officers who complained of ringing in the ears and dizziness were taken to an area hospital as a precaution, but most of them were already sent home, Gonzalez said.

It was not immediately clear what caused the explosion, but it happened during training with the sheriff’s bomb squad, he said.

Helicopter news footage showed a small one-story building encircled by yellow police tape surrounded by grassy fields.

No FBI personnel were injured, said Eimiller.

The FBI Special Agent Jerry Crowe Regional Tactical Training Facility south of Los Angeles hosts firearms training and qualifications tests for the bureau and local law enforcement agencies, Eimiller said.

The FBI will lead the investigation, Gonzalez said.

The Associated Press contributed to this story.

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