I used to grow several varieties of peppers.... with emphasis on hot ! I would carefully cut up the peppers, dry them in the dehydrator, then put them through a pepper mill used only for the peppers. Extreme care had to be taken when working with the peppers ... very hot.
Well, one evening one particular Autumn, I was working on the dried peppers. Kitchen windows were closed....no breeze at all to bother. And then one of my kids came home from dinner at a friend's home. The airflow from the door opening brought enough movement so when I removed the lid from the pepper mill, some of the finely ground pepper dust blew into my face. Suffered a nasty burn on my face from the pepper dust. I would never have believed something like that could happen....but it did.
Lesson learned.