A Metro Transit police officer suffered noncritical injuries in a small explosion Wednesday afternoon during a routine canine training exercise at a bus maintenance facility in St. Paul.

The blast, which authorities termed accidental, occurred just before 3:30 p.m. at Metro Transit’s overhaul base at 515 N. Cleveland Av. The building itself did not burn, and the outside bore no visible signs of the explosion.

The incident occurred as a canine officer was placing a device that had a small amount of explosive material in it for the dog to discover during training.

“For whatever reason the explosive went off,” said Metro Transit spokesman Howie Padilla. “We don’t know exactly why.”

The detonation injured a seven-year veteran of the force, who was taken to Regions Hospital in St. Paul with noncritical injuries. The dog was not hurt.

Nearby buildings were briefly evacuated, and the St. Paul Fire Department’s bomb squad conducted a cautionary sweep of material at the scene that could have posed a further fire threat, but none was detected.

The large building is where bus maintenance and repairs occur. Metro Transit’s equipment maintenance and purchasing departments are also housed there.

Metro Transit’s canine officers conduct weekly training exercises, Padilla said, but have never experienced an emergency like this.

“We’re just really grateful we’re not out here delivering worse news,” he said during an afternoon news conference.

It was a reminder, he said, that even training exercises can be dangerous “and that first responders put their lives on the line every day.”

The blast remains under investigation.