A code term involving the permitted practice of holding a fire door in the open position providing the door closes upon detection. Generally the detection must be from the presence of visible or invisible particles of combustion. Fusible links are not usually considered acceptable because of slower response time. Any listed closer can be used in combination with an electromagnetic holder and a photo electric or ionization type smoke detector. Labeled or listed spring hinges could be used as well as hydraulic door closers. Some special applications of swinging, sliding and rolling fire doors primarily in industrial applications are permitted to be used with fusible links, weights and pulleys. Later product introductions are more sophisticated and provide more flexibility for building operation. These are hydraulic door closers incorporating hold open mechanisms allowing the door to be held open in many degrees of opening positions. The most recent product introduction along these lines is the so-called "swing free" unit. Instead of using a hold open mechanism, the energy of the closer is negated and the door is allowed to be operated as if it were not equipped with a closer. Upon detection of visible or invisible particles of combustion, the closing mechanism engages and the closer causes the door to return to the closed and latched position. These automatic closing arrangements are fail safe in that upon power failure, the door closes. All are listed by a nationally recognized independent testing laboratory and are under an in-plant follow-up inspection service.