Some are preservation vaults but the originals were fire containment boxes (basically) because that film burns insanely well.
It degrades over time, with the plasticizer separating and the film becoming brittle, eventually turning into a powder that can ignite from friction or even auto-ignite. More than anything else, that's why so many early major films are lost. They turned to dust. And then exploded.
> The use of volatile nitrocellulose film for motion pictures led many cinemas to fireproof their projection rooms with wall coverings made of asbestos. Those additions intended to prevent or at least delay the migration of flames beyond the projection areas. A training film for projectionists included footage of a controlled ignition of a reel of nitrate film, which continued to burn even when fully submerged in water. [...] Owing to public safety precautions, London Underground forbade transport of movies on its system until well past the introduction of safety film.
https://en.wikipedia.org/wiki/Nitrocellulose#Nitrate_film_fi...
explosions are another class of reaction.
I was conventional munitions (non-nuclear) maintenance in the USAF. I am trained on these things.
>An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration.
Doesn't have to be supersonic to be an explosion. This is a disagreement about definitions, not about the properties of nitrocellulose.
A dictionary definition of explosion is "a rapid expansion in volume associated with extreme outward release of energy", that includes things like, gunpowder deflagration, aerolized gasoline burning, or even a pressurized container (like a pressure cooker) rupturing. Film burning on a metal tin as they were stored could fit this definition pretty well.
If you're defining pulse wave as a sub-sonic pressure wave, deflagarations can definitely produce those, even with relatively poor fuels (e.g. wood dust). Why do you expect nitrocellulose couldn't? Not enough gas volume?
pulse waves move at the speed of sound and are not propelled by the explosion. an air compressor tank rupturing would produce a pulse wave. pulse waves alone are not fatal to humans, though you definitely feel them and hear them.
- Why would seeing a pulse wave in nitrocellulose prove that it's an explosive (as you claim), if you're defining pulse waves as any sonic wave?
I'm having a hard time understanding your position, or your reasoning for why nitrocellulose isn't an explosive. I also still haven't been able to find any resources that corroborate what you're saying.
So a typical reel was actually a bomb without a detonator.