Authorities say the truck driver lost control of the rig and careened through the wall on the second floor of the industrial building.
The driver was removed from the truck and taken to Elmhurst Hospital, where he is listed in stable condition.
The employee was working on the salt spreader, which was in the sanitation department's central repair shop for regular offseason service, at the time of the mishap.
Emergency responders worked to stabilize the truck.
