Crankcase ventilation?

[MazdaMike]

Its not air, its Positive Pressure in the crankcase. If not properly vented can easily pop out seals like your front main or rear main, or just make every seal leak.
Though most of you may already know the point of the PCV system is to vent that pressure and recirculate it for combustion, not only do oil vapours contribute to airborne HC emissions, I believe they also form a particulate in the air which is also harmful to humans. For the life of me I can't remember why theres positive pressure, all I can remember is the vapors and mist are from the oil sloshing around the crankcase.