When I first started working on the 146, I was told by a very experienced engineer that when starting the apu after a night-stop that it should be allowed to run for a good 20 minutes before selecting bleed air. So that any oil that had accumulated overnight would be burnt off. I also know for a fact that after deicing has been carried out some pilots will run apu bleed air on the first sector!! Then snag the a/c for fumes!!!