There is always this risk in this industry. The dust generated by these operations is very dangerous. If just the right percentage of dust and air are present and given a spark you have a bomb that can take down even the reinforced concrete silos. Because of this danger over the years procedures have been developed to keep explosions at a minimum but it still can happen. Sabotage of protected equipment (for example sealed electrical motors, switches, relays, etc. of course could be compromised) is always a possibility.

I lived in a small community in Michigan. It had large grain elevators and rail service. Probably started up around 1890 or so. Historically I am aware that the grain elevators burnt to the ground on two different occasion, possibly three. A grain mill burned to the ground never to be rebuilt. Portions of Main Street burned down on three different occasions.

That's just one little town and one of the complete destruction grain elevator fires happened in the 70's.

Sabotage?

Hard to say, but if you know how all the machinery works and the systems explosion vulnerabilities it would be relatively easy to destroy one using little resources.