I wasn’t alive then. What started the fire?
Forensic analysis methods are much better now than in 1947.
Did they rule out Arson?
Or was there nothing left of the place to make a determination?
You stated it was too big to be an accident.
You must not understand the explosive power of ammonium nitrate.
If you read some of the links in this thread, you may gain some understanding.
Cheers.