International projectionist (Jan-Dec 1950)

TABLE B. COMPARISON OF PHYSICAL AND CHEMICAL PROPERTIES Property Nitrate Triacetate Estimated storage life Effects ultraviolet radiation Light transmission: Red Orange Yeliow Green Blue Violet , Softening point (approx. ) .... Decomposition temperature ...< Ignition temperature: ( a) Hew film , (b) Old film , Manner of burning 50 years Discolors and becomes brittle. 88^ 88^ 87^ 85% 90° (194° 100° (212° 180° (356° 120° (248° C. J.) C. P.) c. J.) c. Explosive. 1000 years? No change. 90^ 90^ 90^ 90# 88^ 100° (212° 200° (392° 800° (1,472° 800° (1,472° C. »-) C. J.) c? 3?.?) C? P.?) Very slow. the film is separated from the middle portion of the gate, or, to state the matter another way, the distance that the film tracks, or runners, protrude beyond the flat part of the gate in which the aperture is situated. It is therefore safe to conclude that a bad film fire can occur when the film breaks at the intermittent sprocket, or between the intermittent and the aperture. The first effect of the film stopping dead in the aperture is a "burn-out" in from V2 to x/4 second for low-powered arcs (with no significant difference between high and low-intensity lamps) and in about % to 1/16 second for the most powerful high-intensity arcs. In normal operation (24 frames per second) each frame of the film stands motionless at the aperture for about 1/32 of a second when a standard "% to %" Geneva intermittent movement is employed. In front-shutter mechanisms (without rear shutters) the film is exposed to the light beam for slightly more than 1/32 of a second, and in rearshutter mechanisms for about 1/48 of a second. Because the film gate, itself, becomes twice as hot in a front-shutter than in a rear-shutter mechanism, the use of frontshutter mechanisms in theater projectors is to be condemned. (This, of course, does not apply to machines having both front and rear shutters for the purpose of effecting a more rapid cut-off of the bght.) Excessively hot gates not only increase the likelihood of disastrous film fires, but cause physical damage to the film. Defective and worn projection equip ment is an important cause of film fires, and so, too, is even the newest and best equipment when it is manned by incompetent and unskilled projectionists. But possibly the most important troublecausing factor is the circulation of torn, brittle, badly worn, and imperfectly repaired prints. Although the automatic fire-shutter is by no means a great protection against film fire, the faulty operation of this device undoubtedly increases the risk of fire when nitrate film is used. Accidental contact of the film with hot machine parts when threading has caused serious fires; as has, also, smoking by the projectionist while threading or rewinding film, and the placement of heaters, unshielded radiators, and spark-emitting motors or switches near the rewinder or film cabinets. Placing hot carbon stubs in a receptacle on or near the rewind bench or film-storage cabinets is likewise risky business. Important Safety Rules Observance of the following rules by the projectionist will help reduce the possibility of film fire. 1. Do not smoke in the projection room. 2. Thread the projectors carefully, and always check the film path by turning the hand-wheel. 3. Do not permit film to come into contact with heated projector parts when unwinding a length of leader from the upper reel preparatory to threading. 4. Repair prints carefully, checking every splice, and use only the very best nitrate film cement and a clean, perfectly adjusted splicer. 5. Refuse to project films too defective to be repaired in the time allotted for film inspection. (When receiving bad prints immediately notify State or municipal authorities.) 6. Keep films away from radiators or heaters. 7. Guard against dropping hot carbon stubs onto film. 8. Do not throw carbon stubs into the film waste can. 9. Immediately close the lamphouse douser after each shutdown. 10. Do not allow dirt to collect and jam fire-valve rollers, and keep all projector parts absolutely clean and in perfect adjustment. 11. Do not use matches to probe dirt from a loaded projector. 12. Keep the magazine doors of a loaded projector closed at all times. 13. Keep all films which are not in use or being inspected in the fireproof storage cabinets provided for them. 14. Do not lay a hot soldering iron on the rewind bench or near the film cabinets. When a reel of film ignites, the com(Continued on page 32) TABLE C. COLOR SCALE OF TEMPERATURE Approximate Temperature Color Centidegrees Fahrenheit Incipient red heat 500 930 Dull red heat 600 1,100 Bright red heat 800 1,500 Orange -yellow heat 1,100 2,000 Yellow-white heat 1,600 3,000 Bright white heat 3,500 6,000 Blue -white heat 10,000 to millions. 18,000 to millions. INTERNATIONAL PROJECTIONIST • February 1950