Anhydrous ammonia - 2 - 12,000 gallon storage tanks per reporter who saw the permit. Anhyd ammonia is ntypically non-flammable. So they are correct in their filing on that.
Anyhd ammonia can explode, but it has a very tight explosion range, between 13-15 wt percent. Because of this, ammonia explosions are rare. They usually happen when there is a ready flame source (as there was with the huge fire in this case) and the vapor relase is contained somehow (usually indoors).
They also had nitric acid, and perhaps made the ammonium nitrate directly on the site.
Amm nitrate is also not very explosive (unless it is mixed with fuel oil - See Timothy McVeigh and Ok city) (See also the Texas City disaster).
So absent a planned terrorist attack, they should have been correct.
http://svasd.com/images/1pm_Williams.pdf
Amm nitrate is also not very explosive
The people of Texas City will greatly disagree.
The Texas City Disaster
http://www.local1259iaff.org/disaster.html
Ammonium nitrate is highly explosive if a large volume of it is contained within a strong container such as a ocean freighter.
Through the 1940's there were several ammonium nitrate explosions in bulk cargo ocean freighters.
Texas City is our worst example. Changes in the manner of loading and shipping prevented further disasters like Texas City.
I once worked at a chemical plant that made ammonium nitrate and di-ammonium phosphate. There was the ammonia plant where the natural gas was pumped in. There was a phosphuric acid plant. And there was a urea plant. I assume there were nitrates being brought in from somewhere.
Anyway, we smoked all over the place and nobody seemed to worry about an explosion.
Anhydrous ammonia breaks down at 400 degrees.