class I – dusts that ignite and propagate flame readily;
Well, that's where flour gets interesting. Ordinarily it wouldn't qualify - you have to get a pretty specific air/dust mix before the magic happens.

The risk areas will generally be where it's being milled or moved and you end up with a suspension of fine flour in the air.

As it turned out in this instance, the flour is stored in bags in the storeroom (so we're not in a silo situation) and the only area where flour is poured dry is into the dough maker - and that certainly isn't producing the type of flour saturated atmosphere that would be cause for concern.

Now if we were talking gunpowder, different story.