They're a significant fire hazard which is why ATF regulations for stills require them to be located at least 100 feet from a residence.

I live in a city with 2 distilleries. You can smell when they're dealing with the mash because everyone in town can smell it. Also, we all get some black mold (not the really bad one) all over our siding which I think is some byproduct of the fermentation step.

My father worked in the oil business. As a chemical engineer, he was brewing his own moonshine (Poitín [pronounced 'poh-cheen'] in Ireland, Sidiki [means 'friend'] in Arabic language countries) since he was in university. In Saudi Arabia, there were frequent home fires in the western-expatriate communities. Newspapers reported them as "unattended cooking pot" fires. It happened several times per year in the Ras Tanura community they last lived in.