The August 2020 explosion in the port of Beirut—understood to be one of the biggest non-nuclear explosions in recorded history—killed over 200 people and injured over 6,500, while devastating large parts of the city. Lebanese and international authorities quickly came to the same conclusion: The vast quantities of ammonium nitrate stored in warehouse 12 were detonated by a fire that was the consequence of shoddy welding work that had been carried out by Syrian workers on site earlier in the day. Building on our previous investigation with Mada Masr into this deadly explosion, in which we mapped the progression of the fire, the epicentre of the blast, and the layout of the contents stored inside the warehouse, Forensic Architecture and the FFA Investigative Unit looked into the validity of these widely circulated claims about the origins of the fire.