Re: how do flour/grain factories build up static electricity?

Good Question!
The flour mills or grain elevators build up static electric charges on the 
individual grains of wheat dust.  This occurs because the dust particles 
are constantly moving and collide with each other.  When this happens a bit 
of electric charge is transferred from one particle to another.  If the 
process goes on long enough, you can have many kilovolts difference across 
the grain container.  This is enough to cause a static discharge just like 
lightning and since grain/grain dust is flammable, a very powerful 
explosion can follow.