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History and development

35 mm fire hazard  

For the first few decades, 35mm motion picture film was produced on a durable, yet combustible, nitrocellulose base. The material was extremely wear-resistant, but extremely fire and even explosive: the film was easily ignited and burned even without oxygen, emitting toxic gases. One of the first fires caused by her, which killed 124 people, occurred in 1897 at a charity bazaar in Paris. In 1907, the number of victims of a fire in a Parisian cinema also exceeded one hundred. Four years later, a similar tragedy happened in the city of Bologoye of the Russian Empire. This feature of the film has left its mark on all cinematographic technologies. Cinemas began to be built according to special projects that ensured reliable separation of the control room with film projectors and the auditorium. The projection windows were equipped with emergency metal shutters, and the film was placed in special projector cases with a sealed tape path. The fire damper, which automatically lowers in front of the light source when the film breaks and the mechanism stops, has survived to this day as a mandatory attribute of 35-mm film projectors. The use of 35 mm film in amateur cinematography was limited until the advent of the safe substrate in 1948.

Despite all precautions, major fires, caused by nitrocellulose film, occurred regularly. In 1948, a fire on the motor ship Pobeda, which happened for the same reason, claimed the lives of 42 people, including the Chinese Marshal Feng Yuxiang. In 1952, Kodak, and then all other manufacturers, completely discontinued the production of combustible film, replacing the substrate material with cellulose triacetate. Unlike 35mm film, most of the other formats that came later were immediately released on a secure basis. At the beginning, the material was cellulose diacetate, which was inferior to the nitrate substrate in strength and wear resistance. It was used for amateur 16mm, 9.5mm and 8mm films, which are subject to less wear and tear due to low speeds and loads. With the advent of cellulose triacetate, which is comparable in its most important parameters to nitrocellulose, it has become the standard substrate material for most films that have received the designation "Safe" or "Safety Film".

Modern varieties of 35-mm film, in addition to negative and some counter-type ones, are produced on a non-shrinkable polyester substrate. The polyester backing is highly durable and wear-resistant, but it requires special gluing presses with ultrasonic welding. For ease of installation according to the "classical" technology, the corresponding types of film are produced on a triacetate substrate that can be glued with ordinary film glue.