Cellulose triacetate or safety base completely replaced cellulose nitrate as the material used for motion picture film base by 1951-52, primarily because of flammability concerns. At that time, it was thought that acetate base was far less vulnerable than nitrate to long term decomposition and deterioration. And, while this is basically true, it wasn't until the 1980's that scientists began to understand the reactions surrounding acetate deterioration. This deterioration has become known as Vinegar Syndrome.
Cellulose triacetate is the product of a chemical reaction between cellulose and acetic acid.
Vinegar syndrome is the reverse reaction of the breakdown of the acetate. It's this acid that produces the characteristic vinegar odor. Excessive moisture and acetic acid are the prime catalysts for the reaction. Once the reaction begins, it can't be stopped. In fact, it speeds itself up, growing faster and faster.