What is the temperature rating for UL 3 hour fire door?
The length of time of the fire rating basically refers to how long the door prevents the fire from spreading through it. Most locksets are equipped with a “Fusible Link” that melts around 338 degrees F and from that point on prevents the latch from being able to be retracted, thus keeping the door closed. Mortise locks are generally equipped with either a lead or plastic pin that melts away and allows a blocker arm to move behind the latch. Cylindrical locks generally have levers made out of zinc that melts quickly. The fusible link is especially necessary when dealing with lever trim. One scenario that needs to be prevented is the possibility of something inside of the room falling onto the lever and opening the door.
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