(under the class definition) Device comprising a course of travel which confines the user thereto, and a plurality of closures spaced at intervals along the course, and used in turn by the user passing from one end of the course to the other, e.g., an air shaft having a hatchway on successive floors or "air locks" from ambient to a special atmosphere.
SEE OR SEARCH THIS CLASS, SUBCLASS:
49, for a closure in a passageway combined with a means to restrict the direction of travel or number of users.
50+, for a grille mounted face to face with a closure and mounted in the same opening.
61+, for two or more closures mounted face to face and occupying the same opening.
93, for interconnected closures on opposite approaches to a crossing.
