This stuff is propellant. If not confined into a cannon barrel where the pressure can build up, it is not going to cause an explosion.
A big hot fire, yeah, it could happen. But that would not endanger the countryside for miles around.
I think that the mass evacuations were a bit of over reaction, although I can understand that nobody wanted to be the one who said "Aw, it's safe in your house a mile away."
“There’s a rattle in my glove box,
A Federal twelve-gauge slug.” – Adam Carroll in song Porter Wagoner