Concerns about nitrate-based vintage negatives

[thecatspajamas]

Has anyone ever heard of photography nitrate film spontaneously combusting like this? Every incident that I have heard of was related to movie film doing this, and my understanding was that the spontaneous combustion necessarily involved having a high concentration of degrading film confined in a small, relatively airtight space so that the fumes given off by the degrading film remained in high concentration rather than dissipating into the surrounding air, and that high concentration of fumes actually accelerated the degradation of the film. The tightly wound reels of movie film stored in metal canisters provided just such a situation, but I don't recall ever hearing of photographic film spontaneously combusting. That's not to say that one couldn't orchestrate conditions that could lead to it, or that it has absolutely never happened with photographic film (I really would like to hear of any incidents anyone may be aware of), or even that I am any kind of expert on the chemistry involved, but I don't think of the nitrate negatives that I have on hand as ticking time bombs.

In addition to any incident reports, I'd also be interested in seeing what degrading nitrate film actually looks like so that I know what to be on the lookout for.