Police said a suspected thief started shooting when he was caught in the act.
It happened just after midnight Tuesday at the Red Cross building at 1450 Newtown Pike.
Jim Green, a retired safety officer, said he was picking up his wife from work when he noticed an open storage building and a suspicious man in the parking lot nearby.
Green yelled at the man, who ran away to a truck that was waiting for him just down a hill beside the Red Cross.
Green said he went to the top of the hill and kept yelling. He said someone then shot at him from the vicinity of the truck.
Green got out his own gun and shot back. No one was hurt, but the suspect and whoever was waiting inside the truck drove away quickly.
Red Cross management hasn't yet determined if anything was taken from the storage building.
Police are still searching for the suspect.