International projectionist (Jan-Dec 1950)

400 200 100 = TIME FIG. 3. Temperature during the critical period of spontaneous ignition. at the time was 106 F. Subsequently, with the ambient temperature at 120 F., another roll of film ignited. Lowest Ignition Temperature 106 F. Tests made by the National Bureau of Standards have not yet been completed, but so far some important conclusions can be drawn. Self-ignition temperature, which is dependent upon a number of factors, was not the same for any two samples. The lowest temperature leading to ignition was 106 F. Because the number of samples investigated was small, it is doubtful whether this is the lowest temperature at which a reel of film can self-ignite. One reassuring aspect of the results of the tests to date is that no film in good condition has self-ignited. At the moment, no one can predict what the weather conditions will be during the coming summer, and it is quite possible that other regions may be confronted with abnormally high temperatures such as prevailed in the Atlantic Coastal Region during last year. This possibility offers the chance that there will be a recurrence of regrettable film fires. The hazard should not be underestimated, for, even with abundant water supplies, cellulose nitrate fires are difficult to combat. Nitrate base film contains oxygen in chemical combination and does not need additional oxygen to sustain combustion. Furthermore, the fumes given off by its combustion are highly toxic and seriously hamper the fire fighters. They contain oxides of nitrogen which, if inhaled, can be fatal. Shortage of municipal water supplies in many areas presents an acute control problem definitely requiring the constant maintenance of every safeguard. The results obtained in the Bureau of Standards tests indicate that good film does not self-ignite at ordinary storage temperatures. Therefore, the logical approach is to remove from storage all film showing signs of deterioration. Such film can readily be found by regularly scheduled inspection of stored film stocks. Inspecting personnel should be trained to recognize decomposing film by appearance, with its condition classified according to the following categories. Various Stages of Decomposition In the first stage of deterioration the photographic portion usually shows an amber discoloration with fading of the picture image. In the second stage, the emulsion becomes adhesive and the film convolutions tend to stick together during unrolling. Rolls of third-stage film have annular portions which are soft, contain gas bubbles, and emit a noxious odor easily recognizable. In the fourth stage of deterioration, the entire film is soft, its convolutions welded into a single mass, and frequently its surface is covered with a viscous froth. A strong noxious odor is given off, unmistakable to inspection personnel when once identified. In the fifth and final stage, the film mass degenerates partially or entirely into a brownish acrid powder. Deteriorated film in the first and second stages is photographically reproducible. If the matter recorded is important, the film can be copied and the original disposed of. If the material is not valuable, the film should be disposed of at once. Adhesiveness prevailing in deteriorating film may cause the emulsion to become detached from the base while unrolling. This frequently can be prevented by slowly unrolling the film in a bath of carbon tetrachloride under precise laboratory control. This should be done only in adequately ventilated areas. In the third stage, only small portions of the film may be reproducible. The reproducible portions should be separated, if valuable, from the rest and copied. After reproduction, the entire original film should be immediately destroyed. In the fourth and fifth stages, film is photographically worthless and should be destroyed at once without further consideration. Recommended Disposal Methods Films of stages three, four and five, designated for disposal, should be immediately submerged in water-filled drums. They should be carried in these drums to a remote, uninhabited area approved by fire authorities and destroyed by burning. The ground on which the film is to be burned should be free of brush, grass, leaves and combustible litter. Burning should be confined to batches of not more than 25 pounds, as the heat (Continued on page 30) FIGURE 4 Sample of film in the third stage of decomposition. 12 INTERNATIONAL PROJECTIONIST AUGUST 1950