Journal of the Society of Motion Picture and Television Engineers (1950-1954)

ties of film one from the other with a nonconductor, such as asbestos, wood, cardboard, plastics and other insulating material. Conductivity is obtained by storing the film in metal cans, on metal shelves, and in metal containers, such as steel drums. In other words, film should be kept away from metal as far as is practical and surrounded only by nonconductors such as those enumerated. If under these ideal conditions a film does ignite or explode, due to deterioration from one cause or another, the fire is then confined to a small area. April 13, 1950 JOSEPH H. SPRAY Re: Mr. Spray's letter above. We do not doubt that, under certain unusual conditions, new film can ignite spontaneously. Spontaneous ignition is the result of two phenomena, heat generation and heat dissipation. Heat is usually generated by some exothermic chemical reaction and is dissipated by conduction, radiation, and connection to the surroundings. When the rate of heat generation exceeds that of heat dissipation, the temperature of the material rises until ignition occurs. We understand that in Mr. Spray's plant the emulsion was removed from cellulose nitrate base film by washing in a hot caustic soda bath. The washed film was then cut to lengths and packed. The soda-ash residue that remains along with the film may react with it to generate more heat than is usually the case. Also, because of higher temperatures which prevail in certain parts of the plant, heat may not be dissipated as rapidly as desired. Under such conditions, material may self-ignite when it would not do so in normal storage. The paper, "Spontaneous Ignition of Decomposing Cellulose Nitrate Film," was written with an eye toward the prevention of fire in libraries and film exchanges. We still believe that under conditions prevalent in such installations, new film will not self-ignite. The correspondent's contention that excessive nitration may be a cause of spontaneous ignition is interesting and should not be dismissed without careful study. However, there is the belief that because of the modern quality control methods used in the manufacture of nitrate film a uniform product results. Besides, if variation in the degree of nitration does exist, it has not been proven that the autogeneous ignition temperature will be affected. These two factors would have to be studied to confirm or deny the correspondent's hypothesis. We do know that Bureau of Standards investigators were unable to cause the spontaneous ignition of new film at ambient temperatures of up to 120 ° F. We wholeheartedly agree with Mr. Spray that all nitrate film should be stored in insulated facilities under controlled temperature conditions. Engineers of the Interagency Committee for Nitrate Film Vault Tests have devised insulated racks which can, without the aid of sprinklers, contain a film fire to the reel in which it originated. Organizations storing quantities of nitrate film should consider, as a long-range project, the equipping of their facilities with this type of rack. Such a program may take years to execute, however, and will not reduce the danger of film fires in the near future. For that reason we recommend that procedure as outlined in the paper as being the only practical first aid solution to the problem for the immediate future. June 12, 1950 JAMES W. CUMMINGS 766