MARCH 1950 JOURNAL OF SMPTE Volume 54

Spontaneous Ignition of Decomposing Cellulose Nitrate Film

 

BY JAMES W. CUMMINGS

NATIONAL ARCHIVES AND RECORD SERVICE, WASHINGTON, D.C.

AND ALVIN C. HUTTON AND HOWARD SILFIN

NATIONAL BUREAU OF STANDARDS, WASHINGTON, D.C.

Submitted February 9, 1950.

 

Summary—Cellulose nitrate motion picture film in the advanced stages of decomposition is liable to ignite spontaneously. The danger of such ignition is reduced by inspecting stored film stocks and removing and destroying all decomposing film.

 

During the abnormally hot summer of 1949, numerous fires involving cellulose nitrate motion picture films were reported in New York City and adjacent areas. These fires occurred in processing and reclamation plants and in standard film storage facilities. Losses resulting from those fires, other than those of real property, were severe, for the majority of the films destroyed were original negatives and master copies, some dating back to the “silent era.” Due to the fact that these fires occurred either after working hours or on weekends, no casualties to personnel resulted, although some firemen were treated for smoke inhalation.

National Archives and Bureau of Standards engineers who investigated the fires could find no evidence that they were due to the negligence of personnel or the careless use of cigarettes or matches, but rather they appeared to have originated in the spontaneous ignition of deteriorated nitrate film. The summer of 1940 was one of the hottest recorded in the New York area, with the temperature reaching a maximum of 98ºF. The mean high temperature for the months of June and July, 1949, was 83.1ºF, as compared to a normal for the period of 79.3ºF. The rainfall for the entire month of June was only 0.16 in. in contrast to the normal rainfall of 3.33 in. for the same period. The lack of rainfall and the unusually high temperatures of the period seemed to create ideal conditions for the development of spontaneous ignition in film stores.

Prior to the investigation of these fires it was generally believed that nitrate film did not ignite spontaneously at temperatures likely to be encountered in a normal film vault. At the request of the National Archives, the Fire Protection Section of the National Bureau of Standards instituted an investigation to determine the possibility of spontaneous ignition as an inherent hazard in decomposing nitrate film. Samples in various stages of decomposition were supplied by the National Archives for the purpose of simulating conditions which may have prevailed at the fire locations. These samples were stored in a special chamber, the temperature of which was controlled and recorded. The films were packed in individual cans with each wrapped in mineral wool to retain the heat of the exothermic decomposition reaction. The ambient temperature in the chamber was initially 95 ºF and, at intervals, was increased by small increments. After 17 days of this treatment one 1,000-ft reel of film, initially in an advanced stage of deterioration, ignited; the ambient temperature in the chamber at the time was 106 ºF. Subsequently, with the ambient temperature at 120 ºF, another roll of film ignited.

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 106ºF. Because the number of samples investigated was small, it is doubtful

Fig. 1. Container in which reel of film was placed, showing thermocouple wires.

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

Fig. 2. Reel of Film which had spontaneously ignited (during a test it the National Bureau of Standards.

Danger Next Summer

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 then 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 a 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.

Methods of Fire Prevention

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.

Fig. 3. Temperature during the critical period in which a film spontaneously ignited.

Inspecting personnel should be trained to recognize decomposing film by appearance, with its condition classified according to the following categories, 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.

Fig. 4. Sample of film in the third stage of decomposition

Fig. 5. Sample of film in the fourth stage of decomposition

 

Fig. 6. Sample of film in the fifth stage of decomposition

 

 

Disposal of Decomposed Film.

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 lb, as the heat from the burning of large amounts of film creates a strong updraft which may bear fragments of burning film considerable distances to endanger neighboring properties. Under no circumstances should films be burned in an inhabited area or within a building. The rapid production of gases by burning film makes it extremely dangerous, particularly if burned in a furnace or confined space. During test fires in a well vented vault, engineers of the Interagency Advisory Committee for Nitrate Film Vault Tests have recorded pressures as high as 18 psi. It is readily understandable that no ordinary furnace structure could withstand this pressure; its breeching would fail and fill the furnace room with flames and poisonous gases.

Protection of Personnel during Inspection

It is quite possible in the initial inspection that a relatively high proportion of film in advanced stages of decomposition may be found.The opening of cans containing this film may liberate quantities of noxious gases into the working area. Personnel exposed to them may experience nausea, headache, and other unpleasant symptoms if the ventilation is inadequate. It is, therefore, recommended that the personnel working on old film inspection be given ten-minute rest periods each hour in the outer air.

If we are to enjoy freedom from film fires during the coming summer, a comprehensive program of film inspection should begin now so that the task may he completed before the onset of hot weather. Since film is constantly subject to decomposition, inspection should be repeated annually, preferably in the spring. Only by such procedure can we avoid the insidious menace to life and property hidden in deteriorating motion picture film. Particular attention should be given to film of unknown quality or of obscure origin.