International projectionist (Jan-Dec 1951)

Comparative Data Anent Nitrate, Safety Film The appended article complements the data which appeared in IP last month ("New Eastman Identification System for Safety Film," p. 12) and similarly was prepared and is copyright by Eastman Kodak Co. Comment from the field is invited. THE hazardous properties of nitrate film have been well known and understood in the motion picture industry for a long time. Safe practices in the handling and storing of nitrate film have been worked out over the years by the cooperative efforts of various organizations, the National Bureau of Standards, the National Fire Protection Association, the National Board of Fire Underwriters, the Underwriters' Laboratories, the Motion Picture Association of America, and the film manufacturers. Today everyone working in the motion picture industry — whether in studios, laboratories, exchanges, theaters, or projection rooms — is made acquainted with the hazard of nitrate film and with the proper precautions required to handle it safely. As a result, film fires are now remarkably few, and the occasional ones which do occur are usually extinguished quickly with a minimum of loss from personnel injury or property damage. Advantages of Safety Film Despite the relatively good safety record in the industry in recent years, a less hazardous film has been a longsought goal. Its universal use would practically eliminate the chance of a dangerous fire, and it would make possible less rigid safety regulations, less expensive construction, and lower fire insurance rates. The so-called "safety base" or acetate films available prior to 1947 did not have satisfactory physical properties for general theater use. However, now that an improved type of safety support (high acetyl cellulose acetate) suitable for theaters is available in quantity, the use of nitrate motion picture film in the United States is rapidly declining, and existing safety regulations may gradually be moderated. Concern is felt in many quarters that with the time approaching when most motion picture film will be on safety support, but with substantial quantities of nitrate film still in use or in storage, safety precautions may be relaxed too soon or a mistake in identity may be made and a disastrous fire result. Hazards of Nitrate Film The hazardous properties of nitrate film have been described frequently and in detail in the past and are given only briefly here. The most dangerous aspects of nitrate film are its ease of ignition, its very high rate of combustion, and the fact that the gases given off are ex tremely poisonous and. under some conditions, explosive. Nitrate film decomposes readily when heated above room temperature even below the ignition range. The decomposition is both exothermic and autocatalytic, and once it starts it goes faster and faster. The quantity of heat produced is such that, if not dissipated, it may rapidly raise the film temperature to the ignition point. Even local heating at one point can raise the temperature of the film to a dangerous level, thus initiating decomposition in the entire mass. Cellulose nitrate also contains enough oxygen within the molecule so that decomposition or combustion proceeds 1400 1200 rapidly even in a limited air supply, and a nitrate film fire cannot be extinguished by smothering. Nitrate Ignition Temperature Nitrate film itself is not explosive and is less flammable than certain other nitrated compounds. The ignition temperature of nitrate film is generally given as about 300 F, but the exact value depends on the time of exposure, the size and purity of the film, and other factors. Figure 1 shows that in a laboratory ignition test, a sample of fresh nitrate film base which ignited in 80 seconds in air at 325 F, ignited in 10 seconds at 400 F, and in 3 seconds at 500 F. Chemicals left from processing, dirt, and other foreign materials can lower the ignition temperature. The Chemical Warfare Service investigation following the Cleveland Clinic disaster (a nitrate X-ray film fire) in 1929 showed that temperatures of 100 C (212 F) were unsafe for nitrate film, and that exposed steam pipes, unprotected electric light bulbs, etc., were dangerous in rooms containing nitrate film. Nitrate film improperly cared for has caused fires after several hours storage at temperatures as low as 120 F. Spontaneous ignition is also believed to be responsible for a number of nitrate film fires which have occurred in storage vaults in summer following periods of 100 F weather. The actual heat of combustion of ni FIGURE 1 at =5 < Self-ignition temperature in air of Eastman J£j nitrate and high ace S LU ryl acetate (safety) •" motion picture posi Z tive film support. — American Standards z Assoc, test method. 2 1000 800 600 ul 400 200 -\ \ HIGH L ACE ACETYI TATE V * (NO IG NITION ) \ Nl" rRATE 20 40 60 TIME, SECONDS 80 100 INTERNATIONAL PROJECTIONIST • April' 1951 13