I read something earlier that said the explosion was the result of 'dust compression.' I've never heard of that, and suspect it's wrong. It's a volatile atmosphere in the proper stoichiometric ratio and a single spark could set it off.
Compression would be like a diesel engine, and i don't see how that level of compression could occur in a silo.
If'n somebody knows more about a compression explosion in this situation, please enlighten me.