I lost the link to this article that I really liked (on explosives.org) - apparently they removed it. This incident started the tighter regulation of explosives transport. I’m sure you’ll understand why once you read about it. Basically, a driver left a truck unattended overnight, the warehouse next to it caught fire, it blew up taking out 8 city blocks and damaging another 30. Many people died.
Here's an additional article/PDF I found with info (written back shortly after the incident) on what happened, the resulting damages, etc.