Fusible links often play an important role for fire door operation. NFPA 80, Standard for Fire Doors and Fire Windows, 1999 edition, describes the provisions for the use of fusible links. First it is important to understand that a fusible link is two pieces of metal held together by low-melting-point solder. Horizontally sliding doors, vertically sliding doors, rolling steel doors and service counter doors of the rolling type must close automatically upon activation or release of a fusible link or detector. In reference to the example pictured, section 1-10.2 states, “All detectors including fusible links shall not be placed in the dead air space developed at the intersection of the wall and ceiling directly above the fire door.” The dead air space is measured four inches down from the ceiling to the closest edge of the fusible link or four inches along the ceiling extending outward from the corner. NFPA 80 also requires detectors or fusible links to be installed on both sides of the wall, interconnected so that the operation of any single detector or fusible link causes the door to close. Where fusible links are used, one fusible link must be located near the top of the opening, and additional links shall be located at or near the ceiling on each side of the wall. Fusible links located above the ceiling are not acceptable. Refer to NFPA 80 for full text and exceptions.
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