Most grain elevators have incredibly large quantities of dust (basically flour) lying around, it's just unavoidable when you're moving that much grain around.

Most grain elevators have incredibly large quantities of dust (basically flour) lying around, it's just unavoidable when you're moving that much grain around. If it's too dry, there's a risk of static/friction/electrical ignition. If it gets wet, you can have anaerobic bacteria build up heat in a compartment that, when exposed to oxygen, ignites. Grew up on a farm, have a fair bit of experience messing around with grain bins. Our local elevator had a fire due to the former condition, and our neighbor's barn burned down due to the latter.