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i HE PROJECTION ROOM 343
lamphouse is unbearable. Natural air movement may serve in time of cold weather but in the hot summertime it fails utterly to provide the necessary reli
But consider the importance draft it' a fire
in the projection room occurs. By turning on the full power of the ventilating fans as soon as a fire breaks out, the air will be sucked forcibly and rapidly away from the auditorium side and— if the port shutters are closed at once — not even a wisp of smoke or gas will be allowed to pass through the crevices. The audience will not be aware of a fire.
(64) Authorities recommend that projection room ventilation, for reasons of health, should be effected through the theatre's forced draft system where there is one, and that a separate fan and outlet be provided for emergency use only in the event of a fire. If there is no forced draft system, then a fan of proper capacity should be installed in the lower end of the outlet air duct and all inlet air ducts shuttered so that the flow of air may be controlled to meet varying conditions. The Society of Motion Picture Engineers normal venting of each lamp at the rate of 15 cubic feet of air per minute, with an emergency blower capacity of 400 cubic feet of air per minute. These figures apply to lamp ventilation only. For the projection room as a whole a system with a 200 cubic feet per minute normal capacity, and not less than 1,000 cubic feet per minute emergency capacity, is recommended.
(65) In addition to this it is advisable to install an exhaust fan removed from places where fire is likely to originate. It may be installed in a fireproof cabinet in the main projection room, connecting with an outside air duct. Normally this fan is controlled by a switch held in closed position by a spring, but during the hours of operation it is held open against the action of the spring by means of a strong cord, wire or chain attached to the port fire shutter master control. When, in an emergency, the shutter control is released, it will close the switch, thus instantly putting the exhaust fan into action to the limit of its power. The plan is roughly