Update II: Sorry, y'all, last night's update needs an update -- we were a little out of it from the Super Bowl imbibing. It's not clear whether the person using the wheelchair lift was actually in a wheelchair, just that they fell from the lift and were taken to the hospital. [Cue the Benny Hill soundtrack here.] Twenty minutes later, during the initial investigation, the bus lurched forward for some unknown reason, and nailed the fire hydrant with the wheelchair lift. Then the airborne hydrant hit the Muni investigator in the head, who was treated at the scene. Water from the hydrant caused flooding in at least one of the nearby buildings. See SF Appeal for more info.
Update: SF Appeal, of course, has the full scoop on the incident. Apparently, a wheelchair passenger fell as they were being lifted from the 22 Fillmore, and then the bus lurched forward and nailed the fire hydrant. The hydrant then reportedly hit a Muni inspector, who was treated on the scene. The passenger was sent to the hospital for unknown injuries.