CLAREMONT, Minn. (AP) - A 72-year-old man injured in an explosion at a shed holding fireworks near Claremont was upgraded to serious condition on Friday at a St. Paul hospital.

A spokeswoman at Regions Hospital says Harrison "Jim" Freeman was being treated there. He was flown there Thursday and was initially listed in critical condition.

Fire and rescue personnel were dispatched around 2:40 p.m. Thursday after a Quonset hut on Freeman's property in southeastern Minnesota exploded, badly burning him.

State Fire Marshal Steve Wolf says the site is licensed for fireworks manufacturing.

Freeman is the owner of Fireworks Forever. He's a licensed pyrotechnician for the 4th of July fireworks show sponsored by Post-Bulletin Charities in Rochester.

The state fire marshal's office and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives have determined that the explosion was an accident.

Investigators are still trying to find out how the accident occurred.