SMOKE IN COCKPIT AND ACFT AFTER PUSHBACK. RETURN TO GATE.

Narrative

FLT ACFT BEGAN WITH AN UNEVENTFUL PUSHBACK FROM ORD GATE ENG START AND DEP SALUTE. CLRNC WAS RECEIVED FROM RAMP CTL TO SWITCH TO GND METERING. VERY SHORTLY THEREAFTER; I NOTICED WHAT I THOUGHT WAS A BURNING SMELL. I ASKED FO IF SHE SMELLED SOMETHING BURNING. SHE REPLIED AFFIRMATIVELY AND SHORTLY THEREAFTER STATED 'YOU KNOW WHAT; WE HAVE SMOKE IN HERE.' SHE WAS CORRECT AND THE CONCENTRATION OF SMOKE SEEMED TO BE INCREASING. ALMOST SIMULTANEOUSLY; FLT ATTENDANT #1 INFORMED ME THAT THERE WAS SMOKE IN THE BACK AND THEY WERE ATTEMPTING TO LOCATE THE SOURCE. I KNEW THAT NO DEICING FLUID HAD BEEN SPRAYED ON THE ACFT SINCE OUR ARR AND ASKED FO IF THERE WAS ANY SIGN OF DEICING FLUID ON THE RAMP DURING HER WALK AROUND. SHE REPLIED NEGATIVELY. BECAUSE WE WERE STILL A 90 DEG TURN FROM BEING ABLE TO RETURN TO GATE. I INSTRUCTED FO TO INFORM RAMP CTL OF OUR SIT AND THAT WE WISHED TO RETURN TO GATE. CLRNC WAS RECEIVED AND WE TURNED TOWARDS THE GATE -- WAITED WHAT SEEMED AT THE TIME LIKE AN EXCESSIVE TIME; BUT IN HINDSIGHT WAS PROBABLY NOT; FOR A GUIDEMAN AND PARKED AT THE GATE. IN ADDITION TO THE PARKING CHKLIST -- PACKS AND RECIRCULATION FANS WERE SHUT OFF. THE FLT ATTENDANTS SUBSEQUENTLY INFORMED ME THAT THE SMOKE IN THE CABIN SEEMED TO BE EMANATING FROM SOMEWHERE IN THE MIDDLE OF THE CABIN AND HAD SUBSEQUENTLY DISSIPATED. THE COCKPIT SMOKE ALSO SEEMED TO DISSIPATE AFTER REACHING THE GATE. AFTER REACHING THE GATE; I INSTRUCTED THE PAX TO LEAVE THE ACFT THROUGH THE FRONT ENTRY DOOR. A FLT ATTENDANT PA SUBSEQUENTLY INSTRUCTED THE PAX TO LEAVE THEIR PERSONAL BELONGINGS ON THE ACFT. THE EVACUATION PROCEEDED UNEVENTFULLY THROUGH THE JETBRIDGE. AN APPROPRIATE E6 ENTRY WAS MADE FOLLOWED BY A VERBAL DESCRIPTION TO MAINT PERSONNEL WHO SUBSEQUENTLY REMOVED THE ACFT FROM SVC. DISPATCH CALLED THE JETBRIDGE PHONE TO REQUEST DETAILS WHICH WERE PROVIDED.