Fertilizer plant accident in Waco, Texas

I'm reading reports tonight of a plant accident near Waco, Texas. While I would love to speculate, I don't really have enough relevant expertise. I'll be happy to read the Chemical Safety Board report and learn then. I have a few questions:

• What caused the fire that seems to have triggered the blast? At what point should the first responders been pulled back from fighting the fire? 
• Was this a production facility (i.e. anhydrous ammonia to solid ammonium salts?) or a blending/warehousing facility?
• What was the safe distance between the facility and the town, seeing as how some residences were quite close? 

Finally, I really liked this Reddit comment about chemical plant safety:

A reminder to all fellow engineers, maintenance folk, operators and others working at a large chemical facility around the world: 

Sometimes safety programs can be a little over the top and treated as an afterthought or punchline, but they're there for a reason. If you see a dangerous practice or habit, report it. If it's not being addressed, do your coworkers and community a favor and blow the whistle. It may end your job with that company, but it certainly won't end your career. It's our job to protect everyone from the dangers of chemicals that they know very little about. When we fail to do our job together, people die. And I stress together because as anyone who has worked in a plant will know, when these incidents happen it's because of a systemic failure in management, engineering, safety programs, and operations. 

**And this should be considered a world event as this will likely be another incident to learn from. We don't need another Bhopal, Texas City, Flixborough, or San Juanico.

 Well said.