In the early hours of the morning, Company 3 along with other south county units were alerted to a possible commercial structure fire.  While enroute, units were advised by dispatch that smoke was seen coming from the building.  Wagon 7 arrived with a one story commercial structure with nothing showing from the exterior.  Wagon 3 arrived shortly after and staged at the hydrant.  Minutes later command requested a working fire dispatch due puffing smoke coming from the vents.  Wagon 3 secured Wagon 7's water supply and stretched a 3 inch leader line to the Bravo side with a 1 3/4 inch connection.  Ladder 3's crew made access through a roll up door on the Bravo side and after a quick search located the fire at the Bravo/Charlie corner.  After a quick knockdown, crews performed a secondary search and ventilated the structure.  Crews operated for approximately 3 hours before returning to service.