Fire responsive safety door assembly

In a door retention assembly that locks a door in closed position in response to high temperature as during a fire, the door element having an edge portion closable into adjacent relation to an edge portion defined by a header element, there being a strike carried by one of the elements, the combination comprising:

• (a) a latch carried by the other element to relatively move into latching relation with the strike when the door element is closed relative to the header element, thereby to hold the door closed,
• (b) and control means to control movement of the latch into and out of said latching relation with the strike, said means including a heat fusible part that, when fused, renders said control means inoperable to effect movement of the latch out of latching relation with the strike,
• (c) said means including a jamming part directly carried only by said heat fusible part to become displaced into jamming relation with said control means in response to fusing of the fusible part,
• (d) said jamming part being a pin carried by said heat fusible part in a first position wherein said control means is not jammed, and said jamming part is dropped by said fusible part during heat fusing thereof, and into a second position wherein the control means is then jammed.