While stable at ambient temps, it begins to devomposecaround 200c, and critical temp is around 570 c. Between the two temp points, it is giving off volatile combustible gases that create nitric acid and other species. That gas and heat at critical temp creates deflagration, or comm9nly known as an explosion.
No added fuel, caps or firing system required.
It is a dirty orange red blast as the components do not fully oxidize , which is why fuel is added creating ANFO.
That is why they mix it with other materials/fluids.
Like I stated in that post-info from that fellow, the kick was provided by not only heat, but some other catalyst. Maybe the fireworks which I do not believe for one second. I would wager that it was being mixed for bombs and they had the fire and the ignition sources being on hand, exploded. The chain reaction resulted and the rest is history.
BTW, compare this blast the one at Henderson NV years ago. That one was a HUGE explosion from rocket fuel and they actually built the dam plant over a gas line. I do not know if the gas line was active at the time of the explosion or not-I have forgot. But that dam place blew and it was nothing compared to this one. Or the one in TX years ago.
BTW. That stuff is known as ditching fertilizer around the farm parts of Wisconsin.