I'm just spitballin' here, but I've got to wonder whether that ammonium nitrate was being held there until Hezbollah (or their Iranian puppet masters) could figure out the best way to use it against the Israelis. Maybe someone decided to dispose of it before it could be used in suicide bombing attacks???
Apparently, a "customs chief" has officially complained since 2014 about the dangers of holding the ammonium nitrate at the port authority warehouses.
http://www.wbtv.com/2020/08/05/lebanese-confront-devastation-after-massive-beirut-explosion/
Some speculation about an accident from "welding work happening nearby" has recently been put forth, but I don't know if that is a legitimate possibility or not.
http://www.news.com.au/world/middle-east/beirut-explosion-security-sources-say-welding-may-have-caused-deadly-blast/news-story/f6c225aa397145e1cc09c4751ffc026e

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