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660 A. H. NUCKOLLS AND A. F. MATSON [j, s. M. p. E.
It is apparent from the foregoing considerations that when cellulose nitrate motion picture film is used, adequate provision should be made for its safe handling and storage, having in mind the low ignition and decomposition temperature of the film, its extremely rapid rate of combustion, and the possibility of its decomposing with the evolution of explosive and poisonous gases. The importance of complying with the regulations of the National Board can not be overestimated.
Film having a cellulose acetate base was first submitted to the Laboratories about twenty years ago ; and as a result of an extensive investigation, acetate-base film in the form of ribbon for motion pictures was listed as slow-burning, the fire hazard being somewhat less than that of common newsprint paper in the same form and quantity. This type of film, however, did not come into general use immediately, probably on account of the superior qualities of the cellulose nitrate film for photographic purposes. Recently, however, the manufacturers of acetate film have succeeded in improving its qualities to a marked degree, and this type of film is now quite generally used, particularly in projectors of the nonprofessional or miniature type, which may be operated in public without a standard booth if the slow-burning acetate film is used.
The ignition temperature of cellulose acetate is between 700° and 800°F, as compared with about 300°F for cellulose nitrate. A temperature of about 500 °F is required to produce decomposition of cellulose acetate film. In the neighborhood of this temperature the evolution of fumes in material quantity occurs.
The decomposition of cellulose acetate film, however, is not exothermic, as is the case with cellulose nitrate. In other words, the decomposition of cellulose acetate film once started does not continue except under conditions where there is an external source of heat. It will be noted that in the case of cellulose nitrate film the decomposition continues when once started, even in the absence of an external source of heat. This difference between the decomposition of cellulose nitrate film and that of cellulose acetate film is therefore of great importance from the fire and life hazard standpoint.
The cellulose acetate film continues to burn when once ignited if the supply of air is sufficient to support combustion freely. The combustion, however, will cease in a restricted supply of air. The rate of combustion of cellulose acetate film is relatively slow, and the amount of heat evolved is of a low order, being much less than that evolved by paper or wood.