The Swedish ventilation propeller factory (Svenska Fläktfabriken)
started early playing its part to make clean air in the land of my birth, Sweden; the blowing in and blowing out of air in all variations. There most likely isn't a house in Sweden – or meanwhile in all of Western Europe – that doesn't have some kind of propeller ventilation system in perpetual operation.
In SF SF SF SF I'm making reference to this. I place the propeller and its blowing out of bad air –
in various rotation phases – at the center of focus.
At the end, "the shutting off" so as to hear without this "filter", the environmental purifier.
The propeller not as air purifier, but rather – ultimately – as sound purifier !!!