IRVINE, Calif.—Sixteen Orange County sheriff’s SWAT deputies were injured in a training exercise March 13 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 (OCFA) 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, Mr. Gonzalez said.