Fusible Link

A fusible link is a two-part metal connector joined by low-melting-point solder that holds a fire door open during normal daily use. DASMA Technical Data Sheet 255 describes it as two pieces of metal joined by solder rated to release at a specific temperature threshold.

When fire or heat raises the local air temperature to the link's rated level, the solder melts. The two halves fall apart. The hold-open mechanism releases. The fire door closes under its own weight or under spring tension, with no power required.

The standard rated temperature is 165 degrees Fahrenheit. This is low enough to respond quickly to a fire but high enough to avoid false trips from summer heat. Higher-rated links (typically 212 degrees F or above) are used near ovens, kilns, or other heat sources where ambient temperatures can climb during normal operations.

Fusible links are required on fire-rated rolling steel doors and other listed fire door assemblies under NFPA 80. The link sits in the mechanical linkage that holds the door open. This is usually at the counterbalance bracket near the barrel or at a wall-mounted hold-open arm.

A fusible link is a one-use device. Once the solder melts and releases, both halves must be replaced before the door can return to service. Testing the door's self-close function is done with a manual release, not by melting the link.

On commercial rolling doors, the tension wheel must be set so the door can descend freely when the link releases. An over-counterbalanced door may not close all the way in a fire event.