This seems like a more plausible cause. As to why you store a large quantity of it in the center of the city?
A massive explosion shook Lebanon's capital Beirut on Tuesday but there were no immediate reports of damages or casualties.
www.680news.com
"Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was confiscated from a ship some time ago and stored at the port. Local television channel LBC said the material was sodium nitrate.
Witnesses reported seeing a strange orange-colored cloud over the site after the explosion. Orange clouds of toxic nitrogen dioxide gas often accompany an explosion involving nitrates."