The cellulise acetate used for 16mm films up through the 80s has to be kept in humidity and temperature controlled environments or it breaks down quickly into acetic acid which accelerates the process further.

Cellulose acetate film was introduced to replace highly unstable nitrate stock in the 30s. With in a decade of its introduction, archives were reporting significant degradation and it was realized that it needed to be stored in climate controlled conditions. It wasn't until the 80s however that serious efforts were put into preservation or development of better archival mediums.

Of course this was touched on in the article. Wikipedia had more information.