International projectionist (Jan-Dec 1951)

Gases Per cent by volume Nitric oxide (NO) 1.4-8.2 Nitrogen dioxide and tetroxide (N02, N204) 6.9-8.9 Carbon monoxide (CO) 47.7-59.1 Carbon dioxide (COo) 21.3-24.5 Oxygen (02) none Hydrogen (H2) 0.9-3.2 Methane (CH4) 1.0-2 7 TABLE It Gases evolved in Homeless combustion of nitrate film. (Volume of combustion chamber: 8 to 27 cubic ft. Weight of film: 2 lbs. per cubic ft. of chamber.) t From "Proceedings of a Board of the Chemical Warfare Service appointed for the purpose of investigating conditions incident to the disaster at the Cleveland Hospital Clinic, Cleveland, Ohio, on May 15, 1929." U. S. Washington, 1929. trate film is low compared with that of some of the common fuels, as indicated: Heat of Combustion B. T. U. per Lb. 6000-8000 8000-9000 11,620 10,000-14,000 20,750 Government Printing Office, Nitrate Film Wood Alcohol, denatured Coal, bituminous Gasoline However, the rate of combustion of nitrate film is about 15 times that of wood in the same form, so that the heat evolved per minute is initially much greater. This results in a rapid rise in temperature and a very intense fire. A nitrate film fire burns so fiercely and spreads so quickly, it is virtually impossible to control or extinguish it except by automatic water sprinklers. Gases From Ignited Nitrate Film When a single layer of nitrate film is ignited and allowed to burn freely in an excess of air, it burns with a bright yellow flame; but the gases given off are colorless. These are chiefly nitrogen, carbon dioxide, and water vapor, none of which is poisonous or explosive. If the air supply is restricted, as is always the case in practice where film is in rolls in any quantity, the film will burn (with or without flame) and give off large quantities of thick, yellow fumes. These are extremely poisonous and may form explosive mixtures with air. The relative amounts of various gases given off by burning nitrate film in a limited air supply are shown in Table 1 in a number of cases in the Cleveland nitrate film disaster in 1929. The simultaneous exposure to nitrogen oxides and carbon monoxide is particularly serious, since these gases have an additive toxic effect, the ultimate result of which is to deprive the body of its supply of oxygen. The relative toxicity of nitrogen oxides, carbon monoxide, and carbon dioxide is shown in Table II. Safety Film Characteristics So far, all commercial safety motion picture film supports have been made from cellulose acetate or the mxied acetate-propionate or acetate-butyrate cellu Cellulose acetate film starts to decompose with evolution of fumes at 500 F, compared with only 200 F for nitrate film. The ignition temperature usually given for acetate film is about 800 F, compared with 300 F, for nitrate film. Our laboratory tests (Fig. 1) show the high acetyl acetate film base to ignite in 9 seconds at 950 F, and in 2 seconds at 1100 F. At 930 F the film decomposes but does not ignite in this test. The thermal decomposition of acetate film is neither exothermic nor autocatalytic. Furthermore, the burning rate of acetate film is only about 1/20 that of nitrate film. This means that acetate film is difficult to ignite and, if ignited, is easily extinguished by water or smothering. Cellulose acetate plastics containing some of the common types of plasticizers burn about as fast as paper in the same form and quantity. Flame-Retarding Plasticizer However, acetate motion picture film base made by Eastman Kodak Co., contains a flame-retarding plasticizer which greatly slows down the burning. Modern TABLE II* Toxicity of the more important gases evolved in combustion of nitrate film. Symptoms Parts per Million Parts of Air Nitrogen Oxides Carbon Monoxide Carbon Dioxide 1. Slight symptoms after several hours or maximum concentration for 8 hours exposure 30-40 100-200 5,000-30,000 2. Maximum concentration tolerated for 60 minutes without serious disturbance 50-100 450-900 33,000-60,000 3 Dangerous to life in 30 to 60 minutes 100-150 1500-2000 33,000-80,000 4 Kills most animals in short time 240-700 4000 or over 50,000-300,00" * From Jacobs, M. B., "The Analytical Chemistry of Industrial Poisons, Hazards and Solvents," Interscience Publishers, Inc., New York, N. Y., 1941 and 1949. lose esters. It is sometimes thought that the term "safety film" implies that these films do not burn. Actually all of these safety films will burn slowly if held in a flame, but will generally cease burning soon after the flame is removed. They are called safety films because they are Traces of the lethal hydrocyanic acid gas so very much less hazardous than nitrate safety films actually burn much less easily and less rapidly than paper or wood in the same form and quantity. The gases given off when acetate film burns (Table III) are about the same as those given off by burning wood. Of these, carbon monoxide is the greater (HCN) have also been found but only film— the "ignition temperature is much hazard, although the other gases may in insignificant amounts. Complete com higher, the burning rate so much lower, produce suffocation or even severe lung and there is no danger from nitrous irritation if inhaled in sufficient quanfumes. tity. If acetate film is burned in an ex bustion yields about 4 to 5 cubic ft. of gas per pound of nitrate film at normal temperature and pressure. The proportions of these gases will vary somewhat with the temperature, pressure, air supply, and so forth. The toxicity of carbon monoxide is well known; but the physiological effects of the nitrogen oxides (NO, N02 N204) are even more insidious because of their greater toxicity and delayed action. Exposure to concentrations of nitrogen oxides which appear to have no serious effect at the time, frequently cause death several hours or days later. This occurred Gases Physiological Effect Carbon monoxide (CO) Toxic Carbon dioxide (C02) Hydrogen (H2) Methane (CH4) 1 | I Suffocating Acetic acid (CH3COOH) Aldehydes Ketones 1 \ 1 Irritating and Suffocating Alcohols TABLE lilt Gases evolved in combustion of cellulose acetate (safety) film. t From Nuckolls, A. H., and Matson, A. F., "Some Hazardous Properties of Motion Picture Film," J. Soc. Mot. Pict. Eng., 27, 657-661, December 1936. Editor's note : Cases present i» trace amounts only are not shown in this table. 14 INTERNATIONAL PROJECTIONIST April 1951