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May, 1952
PROBLEMS Ol STORING FILM
151
motion of a projector. It should be borne in mind that the film may be already old, and its perforations somewhat torn.
(2) The heating of film by projection illuminants is considerable. Every projectionist knows that the film is sensibly warm when he takes it from the bottom spool box. The heat reaching the film from the small lamp of the editing machine is negligible.
(3) The editing machine is under the intimate control of the user and can
(a)
«b)
be stopped instantly if there is any trouble. Even so there are some films which are in too poor a condition to view, even by this means, and are thus quite inaccessible until they are duped.
The Nature of the Fire Hazard.
Although the industry now almost completely uses safety base, until a few months ago virtually all standard film was made on nitrate stock, and thus the bulk of film in any archive is now on inflammable base ; for many years we shall have to continue 1 to store a quantity of this material, and the
ensuing remarks refer to nitrate film. 1 shall refer to safety film later.
It is common knowledge that nitrate film is dangerously inflammable, but it we look more closely into this we find that its exceptional danger is due to three facts:
(1) It rapidly decomposes upon being subjected to quite a small amount ot heat. A temperature of 230° E. maybe sufficient to ignite even new film.-' Very old film will burn at a much lower temperature, and I shall refer to that later.
(2) The gases evolved from the decom
Fig. I.
(a) Specimen of sticky film showing flux-like distortion of image.
(b) Specimen of film showing damage by water, where the image is destroyed from the edge inwards.
position of themselves form an inflammable mixture. That is to say, oxydising agents are among the gases produced so that once ignited, combustion can continue independently of an external supply of oxygen. In this it possesses explosive properties. (3) These gases, upon burning, generate
a fierce heat. The result is that a film fire cannot be extinguished by the usual means of fire fighting, i.e. the principle of exclusion of air, since the decomposing film supplies oxygen from its own material. The heat generated