Crews were called out to Davis Forklift and Repair on the 100 block of West Globe Street around 2 a.m.
It is estimated that a third of the building is destroyed.
Investigators say they do not know what started the fire, but say that transients often seek refuge in the building.
"Some of them did stay inside the building where the building materials were stored. So that will be a part that we will be examining closely," says Chief Wayne Barber of the Sanford Fire Department.
Another company, called Southern Real Estate, also occupies the building located near Highway 421.
One firefighter suffered dehydration and was taken to a local hospital, but is OK.