Just saying

 earlier this year there was a nitrogen fertilizer explosion.

the thing that detonated the ammonia nitrate was the fire that was going for some seconds. ammonia nitrate is explosive in the right condition. the fire crew that came couldn't put out the fire before the detonation or the fire would have been less costly and fewer casualties would have happened. other things in the nitrogen-based fertilizer was nitric acid, hydroxylammonium nitrate, potassium nitrate, and sodium nitrate. the most explosive thing was the ammonium nitrate with the yellow on the fire diamond as a 3.