Bolt closure maintenance for fire-degraded latching assembly

In a door closure assembly, the combination comprising

• a) a latch bolt element,
• b) carrier structure to carry the bolt element to pivot between door unlatched and latched position,
• c) and means carried by a fire resistant portion of said assembly to be responsive to an increase in temperature to a level T to move into position to block door unlatching movement of said bolt element from door latching position, there being a chamber in said portion of the assembly,
• d) said means including a blocking part urged in a direction of movement of said part into blocking relation to bolt pivoting toward unlatched position, and a meltable element preventing said movement of said part until the temperature of said meltable element rises to temperature T causing melting of said element,
• e) said blocking part comprising a plunger movable in said chamber in said direction, said meltable element also positioned in said chamber, said plunger having a flange and a blocking shank projecting in said direction beyond said flange, and said meltable element is positioned to extend about said shank to obstruct movement of said flange in said direction, said means including a spring in said chamber urging said blocking part in said direction, said meltable part extending annularly about said shank and said spring.