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258 RICHARDSON'S BLUEBOOK OF PROJECTION
for a number of reasons, each one of which deserves the paramount consideration of the architect and theatre owner. It is important to the health and comfort of the men who work for long hours in a confined space under very difficult conditions at best. It is just as important as a safeguard when a fire starts in the projection room. And, unless removed by lamphouse ventilation, the minutely fine particles of carbon powder given off by the carbon arcs will enter the switches, volume controls and tube sockets of the sound system and lodge on the film, producing minute scratches. Adequate ventilation will avoid all these troubles.
(57) Plenty of fresh air should be supplied — not taken from the auditorium, but outside the theatre.
(58) If the room is longer than it is broad, the air should come in near the floor level at each end and find its outlet at the ceiling line at its center, thus sweeping through the entire room. If the room is somewhat square, the air inlet may be at the floor line either at each side or at the rear wall, and the outlet in the center of the ceiling.
(59) The inlet opening in all cases should be covered with galvanized wire screen of about one-half inch mesh.
(60) The inlet openings must have sufficient area to admit a plentiful supply of air. Shutters should be adjustable, so that the amount of incoming air can be regulated at will.
(61) The outlet must have ample area, not only for ordinary ventilation but also, in the event of a film fire, to enable the quick escape of all gases and smoke as fast as they form. (62) Otherwise they will seep into the auditorium, perhaps causing fatal consequences. Gases pass quickly through crevices around the glass covers of port openings. When they can't escape they blind and overpower the projectionist, driving him from the projection room. With the fire out of control anything may happen.
If ventilation is by natural draft, both inlet and outlet must be much larger than where forced draft is employed.
(63) Ventilation, save in exceptional cases, should