MULTIPLE incidents, all showing what a pile of ANFO can do. If they can do that much damage accidentally, and such accidents happened repeatedly, it's NOT a stretch for someone to say "hey, I'll do that intentionally!".
not a bomb in the OKC bombing sense.
What part of "large quantity of ANFO ignited in a confined space equals an OKC type bomb" don't you get? The only difference between the listed accidents and OKC is intent and a rented truck!
what is common knowledge today was not then common knowledge.
BS. That was common knowledge in farming country (gee, lots of fertilizer & desel around: AN + FO + spark = BOOM). I learned it in high school out of the chemistry teacher's textbooks. Farmers used it regularly.
A couple of ANFO bombs have been used in the middle east since OKC, but I don't know of any before then and appearently neither do you.
Didn't you read my post? I listed numerous instances! That they occurred accidentally is largely irrelevant, as they HAPPENED on an OKC scale. Maybe Nichols/McVeigh was the first time it was used intentionally on that scale, but the accidents show that it was simple to do on that scale; was just a matter of time before motivation converged.