A quick history lesson: Back in the late 19th century, Cellulose Nitrate was first used as a film base. It had good characteristics for use as a film base (flexibility, easy to coat, held the emulsion well), but it had one significan drawback: It was flammable. As the film aged and decomposed, it became more flammable. Negatives stored in tight spaces (the proverbial "shoe box") tended to decompose more quickly and give off flammable gases. If the film caught on fire, it would give off free oxygen (thus feeding the fire) and toxic fumes. When it was fresh, Cellulose Nitrate film could be ignited by a cigarette. An old box of negatives could be ignited much more easily.

In the 1930's companies started using Cellulose Acetate as a film base. Because it wasn't dangerous like the old Cellulose Nitrate film, it was called "Safety Film." This was a big advertising point in the '40s and '50s, and old film boxes and the film itself is identified as "Safety Film".

Enough of the history lesson for the day...we now return you to your regularly scheduled program...