A fire damper or the like having butterfly-type gas flow control blades includes a heat responsive blade release assembly that incorporates a standard fusible link accessible from externally of the assembly. The fusible link holds together pivoted side plates of a housing from which extends a pair of arms normally holding the blades in their open positions. When the link melts, the side plates move apart, allowing the arms to open and release the blades. The assembly is also adjustable to vary the extent to which the blades open.