I actually rode along with our second engine out, Engine 252, to a call for smoke in the building. Engine 252 staged on the hard road, there were already 4 engines in and around the building, Engine 152 had the hydrant at the southwest corner. The truck set up to check the HVAC equipment on the roof. A unit on the third floor was found to be the problem. Maintenance workers took care of it. We got things packed back up and returned to the station.