A300
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Returned To Gate; General Maintenance Action
Procedure; Human Factors; Aircraft
After extensive deicing to remove ice buildup from the airplane we waited three minutes to open the bleed air supply. As we were about to start the number two motor we got an aft cargo smoke warning.  I asked the FO (First Officer) to check and see if there was evidence of smoke in the rear of the aircraft. He stated there was a fog/mist in the air in the fuselage of the aircraft. We ask the tug driver to tow us back into the chocks and asked ground control to send [ground personnel] to check out the smoke.    The APU was running when we deiced and I believe the requirement for extensive deicing caused an accumulation of the deice fluid in the APU intake. Training the deice crew to avoid the APU intake. Knowing the amount of deice fluid applied to the airplane we could've waited longer than 3 minutes to open the bleed valves.
I am unsure how the fluid exactly entered the conditioning system. The required time limits post de-icing were inadequate in this case.Due to the extensive de-icing of the AC a longer wait time in these circumstances might be prudent.
A300 flight crew reported receiving a cargo smoke indication during pushback possibly due to deice fluid in the APU intake.