Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human-Machine Interface; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Ground Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Human Factors
Cockpit filled with 'smoke' after turning on packs following de-ice. [The apparent] cause was De-icing fluid must have gotten into the bleed air system. We got some from the APU supplied bleed air. I had hoped that the engine bleed air system was not affected; but it was actually worse. We de-iced during heavy snow and I halted the process when it was apparent that the intensity of the snowfall was such that the entire Type I/Type IV process wasn't sufficient to stay ahead of the snowfall. Turning on the packs with APU bleed air we experienced 'smoke' in the flight deck but none in the cabin. Packs off stopped the problem. We waited 30 mins until the snow lessened and completed de-icing. Hoping that the problem has corrected itself I put the packs on using engine bleed after waiting 3 minutes. However; the 'smoke' returned even heavier. FA's (Flight Attendants) reported a slight smell. We returned to the gate and the aircraft went out of service. Never saw this in XX years of flying.
B737-800 Captain reported a 'smoke' in the flight deck event resulting in a return to gate.  The aircraft was subsequently taken out of service.