Safeguarding the Storage of Photographic, Motion Picture, and X-Ray Films

Abstract

This paper outlines briefly the hazards connected with the storage of photographic, motion picture, and X-ray film of the nitrocellulose variety, and suggests precautionary measures to be taken with these materials. The various kinds of film are described and the effect of heat is discussed, with particular reference to the toxicity and explosibility of the gases developed. Recommendations for proper storage and handling are made, including suggestions for location and construction of the vaults which should be used where any considerable quantity of film is to be stored. Description of film Photographic film consists of a base or support on which is coated a light-sensitive emulsion. This emulsion is a gelatin solution containing very small crystals of silver halide (usually the bromide with a small percentage of iodide), which are formed in the gelatin solution by the reaction of silver nitrate with potassium bromide and iodide. Potassium nitrate, also formed in this reaction, is removed from the emulsion before coating. Photographic processes following exposure in the camera convert the silver halide which has been affected by exposure to light to metallic silver in a very finely divided state and also remove all of the unused silver halide. The metallic silver image is all that remains in the gelatin after this process is completed. For the base either of two materials is used, a solid solution in camphor of nitrocellulose, which is highly flammable and gives off toxic gases on decomposition, or cellulose acetate, which has a flammability comparable to that of ordinary paper. Film made from cellulose acetate is called “safety film” and is not particularly hazardous in storage. Its use wherever possible is, therefore, to be highly recommended. Films for various uses differ in size, thickness, and amount of emulsion. Photographic film for amateur use is generally thin, small in size with a thin coat of emulsion on one side, and with or without gelatin on the other. Most large commercial photographic film is heavier and coated on both sides, to prevent curling. Motion picture film is generally of the same thickness (about .006 inch) and, except for some of the color films, is coated on one side only. Except for dental films, which are small, thin, and usually mounted, X-ray films are relatively thick and have heavy coats of emulsion on both sides. The latter may be as much as 10 per cent of the thickness of the film. The largest size of film generally used in X-ray work is about 14 by 17 inches and .008 inch or more in thickness. Effects of heat Nitrocellulose, which forms the base of “nitrate” films, is a substance prepared by treating cellulose made from cotton with sulfuric and nitric acids. It is thus essentially similar to celluloid and guncotton, being intermediate between these two in nitrogen content.