Some movie buffs value physical media as priceless artifacts, from out-of-print DVDs to rare VHS tapes. Those fans might be shocked at how many classic films are missing, with thousands of original reels accidentally destroyed or deliberately discarded. One issue is that the nitrate stock used in early films is flammable. Such reels ignite with such intensity they can't be extinguished with water, resulting in sometimes fatal fires. Modern movie labs use plastic-based "safety film," but scholars believe that around half of all films released before 1951 are lost, with many destroyed by fire.
Source：https://www.cbr.com/classic-lost-films-london-after-midnight/
