I went through this with some film that had expired in 1947 and that I just exposed 6 months ago. I was able to get results from the film, but after PE explained to me WHY it's so dangerous to keep them in the house, I scanned and then burned all my nitrate negs.
The reason was that he explained that the reaction happens when the film switches from one environment from another, so it could also cause a reaction going from humid and hot to cool and dry, but that it had the most chances of reacting to hot moist temps.
But the biggest and most important thing to remember is that it makes its own oxygen, so even in the freezer, in a sealed container, it can ignight, burn, and catch the whole fridge/freezer on fire.
It's really dangerous to keep in the house (again according to PE) and think about it, are old negs more important than your current images that might be lost in a fire, or your life or your children's lives?
So scan it, and get rid of it... If you look in my gallery, you'll find a shot if my nitrate burning on a picnic table I figured I would document the event.
Admittedly I have a few more unshot rolls of nitrate verichrome, maybe once shot I'll burn them and record it on color film to get more of the burn color
~Stone | Sent w/ iPhone using Tapatalk