Quote Originally Posted by Dan Henderson View Post
My understanding is that flammable nitrate-base film was replaced with a more stable acetate base, which was safer, and marketed as "safety film." I have never known just how flammable it was, whether it would spontaneously ignite perhaps after some time to oxidize in air, or if the heat of a movie projector would ignite it, or what.
That's correct....the nitrate film is VERY inflammable and needs no oxygen to continue burning once lit. It also decays readily and becomes very unstable. Despite precautions, there were some horrific accidents in the early days of movie theatres.

As regards the Kodachrome found by the OP, there is no chance of it now being processed or even being usable. But it's very collectable, and, if the box, etc., is in good condition, it's really a museum-quality item.