FWIW flour is potentially explosive. The attached isn't a great example, but a google search will turn up plenty of very dramatic incidents
-Target
In the surroundings of the place where I grew up, is a company that produces feed for farm animals. On their main lot are 5 separated production facilities where on each bottom 2 lorries can park to be charged with the end product, and next to that parking space is the production facility and a 60 meter (180 feet) high silo. Those silos 15 meters at their widest and made of concrete. On top there is a venting hole that is covered with a concrete slab of about 50 square meter.
Well, the mixture of air and particles inside that silo went wrong once. Because of the venting hole the silo didn't break, but the explosion was heard 10 kilometers away and people found that concrete slab 1 kilometer away from that production facility.
It is the mixture: amount of particles per volume unit of air and a spark. That is really nothing more to it. Works with almost anything, as long as the mixture is right. Powdered coffee creamer is another fine example of getting a really violent reaction.
Here is a Mythbuster's video about that:
https://www.youtube..../watch?v=yRw4ZRqmxOc 
