International projectionist (Jan-Dec 1957)

CINCE 1950 all motion-picture film ** produced by the major U.S. and Canadian manufacturers for professional and amateur use has had a "safety" base of cellulose acetate or other material which burns slowly. Formerly, most film was made with a film base of cellulose nitrate. There still seems to be some confusion over the differences between these two types of film. Where "safety" film is used or stored exclusively, no special fire protection precautions are necessary. While the change to acetate base film has been an accomplished fact domestically for about six years, some cellulose film is still in circulation and some nitrate film will be in storage for years for archival purposes. The NFPA Standards for the Storage and Handling of Cellulose Nitrate Motion Picture Film (NFPA No. 40) should be followed to safeguard life and property where this nitrate base film is being stored or handled. This article illustrates the difference in the ignition and burning characteristics of the two types of film. It FIG. 1. Nitrate film 15 sec after ignition. should be understood that cellulose nitrate contains chemically combined oxygen, sufficient in amount so that this material can partially burn or decompose without the presence of air. The gases formed by such decomposition are both toxic and flammable and may be produced so rapidly as to jReprinted from the October 1956 Quarterly of the National Fire Protection Association, Vol 50, No. 2. NITRATE versus ACETATE FILM SAFETY A series of tests conducted by NFPA emphatically illustrates the combustion differences between the old and the new film. By ALLEN L. COBB Fire Protection & Safety Dept. Eastman Kodak Company create a hazard to life and dangerous pressures in enclosed spaces. While the actual heat of combustion of nitrate film measured in British Thermal Units per pound is 6,000 to 8,000 compared with 8,000 to 9,000 for wood, the rate of combustion is about fifteen times that of wood in the same form. Cellulose acetate film, in contrast, burns relatively slowly— about the same speed as paper — and the combustion products of burning safety film are much less toxic than the gases of cellulose nitrate. Loose-Film Burning Tests At a series of tests, comparisons were made of the burning characteristics of nitrate and acetate films. Figure 1 shows the extent of a fire 15 sec after ignition of a pile of 1,000 ft of 35-mm nitrate motionpicture film which had been placed in a loose pile on the ground and ignited. The burning time was checked with a stop-watch at 38 sec. The nitrate film was completely consumed. Flames reached a height of approximately 12 ft and gave off no visible fumes but did show some fly ash. In a comparative test, 1,000 ft of 35-mm acetate motion-picture film was placed in a loose pile on the ground and ignited using a small wad of wood excelsior. Figure 2 shows the resulting fire at its height. The burning time was recorded at 218 sec. The safety film was not completely consumed and showed evidence around the edges of melting and curling. The flames of the safety film did not exceed two feet in height and gave off a black smoke. About 1,000 ft of heavy craft paper, 35-mm wide, was placed in a loose pile under similar conditions. In this case, the burning time was checked as 124 sec. The flames were approximately two feet in height and considerable blue smoke and fly ash were observed. About 1,000 ft of cotton fabric, 35mm wide, was similarly ignited. Burning time was 155 sec; flames did not exceed two feet in height; very little fly ash was observed although there was some blue smoke. Simulated Projector Fires Two Simplex projector magazines were mounted on a frame in a such a way as to simulate the mounting distance which could be found on a theater projector. Acetate "safety" film, a full 1,000-ft roll) was placed in the top magazine with a strip of film lead FIG. 2. Acetate film at height of fire. ing down to the lower magazine which contained part of a roll of acetate film. The lower magazine door was left open and film was placed in a disorderly pile beneath as might be found in a theater following a film break. This small pile of film was ignited with a wad of excelsior and it was observed from Fig. 3 that while much 30 INTERNATIONAL PROJECTIONIST • MARCH, 1957