If you notice an odd smell coming from films, or one film in particular, then there is a chance that the films have started to deteriorate (all films have a slight `chemical’ smell which is normal). Smells like vinegar or strong mothballs are indicative of deterioration of acetate-type bases. Other problem indicators are small white or clear crystals appearing on the film’s surface, a large degree of curling in on themselves, or the emulsion layer flakes off during handling.
Nitrate base films give off a strong unpleasant odour slightly reminiscent of chlorine bleach. The image will start to fade to a brownish sepia colour and may disappear completely in places. The film will become sticky and eventually turn into a brownish dust. When nitrate film decomposes it becomes more flammable and advice should be sought from an appropriate source such as the Archive or your local fire authority regarding dealing with the film.
If your films start to show any signs of deterioration or mould forming then the best course of action is to separate the particular cans that exhibit the warning signs and seek expert advice.