stored in a port next to a large city for 6 years.
What could possibly go wrong?
Quick Google:
"At high enough temperatures, however, ammonium nitrate can violently decompose on its own. This process creates gases including nitrogen oxides and water vapour. It is this rapid release of gases that causes an explosion. Ammonium nitrate decomposition can be set off if an explosion occurs where its stored, if there is an intense fire nearby."
In the video, you can see a huge bubble of white vapour spreading rapidly, I'm assuming that is water vapour.
It's the shock wave that does the damage.
I wonder if other places store this chemical in large amounts near built up areas? (Answer = yes.)
Also from Google:
To put the destructive power of that amount of the chemical into perspective, it was 2200kg of ammonium nitrate Oklahoma City truck bomber Timothy McVeigh used with deadly intent in 1995. The Beirut pile of the chemical was more than a thousand times larger than McVeighs bomb.
Damage done by McVeigh's bomb:
https://www.stripes.com/news/us/long-before-the-oklahoma-city-bombing-timothy-mcveigh-sent-a-warning-1.625884/mcveigh-2-1.625885