[Cuttnhorse]

The fact that pure AN is not used commercially as a high explosive, e.g. because it’s better mixed with fuel oil, does not alter the fact that the pure material itself is capable of detonation.

But, doesn't AN when it burns have to be in a confined space to detonate? Can fire actually cause detonation in a non-confined space??

I have burned a lot of old dynamite...makes a great fire, but will NEVER explode if burned in the open...lots of flame and smoke, but no boom!

I have also used many tons of ANFO in mining applications, (love the stuff) and being in a drill hole confines the gasses and results in detonation.

Is that correct?

My guess is the AN caught fire and the Hezbollah fools had rockets or rocket propellent in the building and that was the explosion.
Note the color of the flame and smoke...never seen ANFO send up an orange smoke cloud in a mine shot.

[coloradan]

The red color is nitrogen dioxide, a very toxic oxidizer, which is typical of AN explosives when there isn’t enough reducing agent, e.g. fuel oil, added. Correctly-mixed ANFO has enough fuel oil to consume all the oxygen in the AN, leaving none remaining to form nitrogen dioxide. Smoke from the resulting explosion would lack its characteristic red-brown color. The fact the Beirut explosion cloud was deeply red-brown indicates an AN explosion without much (or any) fuel oil, i.e. possibly just pure AN.