A southern Minnesota history center avoided an explosive exhibit on Thursday when authorities helped remove three live World War I-era incendiary devices that had sat undiscovered in the collection for more than half a century.

The History Center of Freeborn County said police from Albert Lea and a bomb squad from St. Paul responded to the museum after three live explosives were found in its collection.

The center's Executive Director Stephanie Kibler said employees were conducting a routine weekly examination of collection boxes when they found the first grenade. 

"We find things often, but nothing quite as hazardous as a grenade," Kibler said. "We just immediately called the Albert Lea Police Department and they were on site within a matter of five, 10 minutes." 

The Albert Lea Police Department said a sergeant responded just after 10:30 a.m. 

Kibler said four more items were found in subsequent boxes — two deactivated explosives and two potentially live ones. Using the museum's records and the internet, the live items were identified as two grenades and a mortar, all from World War I-era Germany.

The live items "had no markings or drilled holes to suggest" they were deactivated, police said.

The history center closed for safety reasons, and the St. Paul bomb squad responded to help. 

Museum staff said the explosives had been there since the 1960s. The bomb squad removed them without incident.

While the explosives were an extraordinary occurrence for the museum, Kibler said there are plenty of other interesting things to see for those visiting.

"We have a terrific collection and we have wonderful exhibits and we do have a very nice military exhibit," she said, "but it does not contain live grenades."