Abstract: The panic exit device includes several features which improve its ease of use and operability over earlier devices including: (1) an improved latch deadlocking mechanism; (2) an improved latch to pad mechanism; (3) a pad lock down feature; (4) an improved universal mounting plate and easily mounted strike; and (5) a vertical rod-bottom bolt deadlockig mechanism in its center case. The latch deadlocking mechanism includes a deadlock link, which in the event of a fire, will block the movement of the latch bolt.

Abstract: Fire control systems and release mechanisms. The release mechanisms of the present invention comprise a digital logic circuit for processing signals which are indicative of a condition in an outside environment, and for providing a trigger that will actuate the mechanical release mechanism in response to the condition, a power circuit for providing regulated power to the electronic circuit in response to the input power, the regulated power being used to operate the digital logic circuit, and a power backup circuit interfaced to the power circuit for providing the regulated power for a predetermined time in the event of an input power failure so that the digital logic circuit can be operated for the predetermined time during the input power failure.

Abstract: In a door closure assembly, the combination comprising a latch bolt element; carrier structure to carry the bolt element to pivot between door unlatched and latched position; and means carried by a fire resistant portion of the assembly to be responsive to an increase in temperature to a level T to move into position to block door unlatching movement of the bolt element from door latching position.

Abstract: A first platform having fingers rising therefrom is interengaged with a second, fusible platform in a spring latch assembly. The second holds the first at an angle in which the fingers avoid notches formed in the tail of the latch bolt. When the fusible platform melts due to excessive heat, the fingered platform assumes a normal horizontal disposition, and the fingers engage the notches in the tail to prevent the latch bolt from retracting.

Abstract: An emergency door, such as a fire door which closes automatically in case of fire, includes a nose piece which moves to an extended position when the door is closed to provide a seal of the gap otherwise present between the forward edge of the door and an adjacent door frame or door, and generally also interlocks with a mating portion of the adjacent frame or door. An addition latching element may be provided to extend from the top edge of the door and be received in a keeper when the door is closed. Door operating hardware, preferably all mounted interiorly of the door except for a push bar on one side of the door and a door handle on the other side, is operable to retract the nose piece and latching element when it is desired to open the door. The nose piece and latching element are held in retracted position when the door is open. A release device releases the latching element and nose piece to extend to extended position when the door is moved to a closed position.

Abstract: A latch device includes a pin slidably engaged in a housing. The pin includes one end for engaging with a retainer so as to lock a door panel in place. A spring member is engaged between the pin and the housing and is made of shape memory alloy and is deformed to a shorter or longer length different from an original length so as to allow the pin to engage with the retainer. The spring member may be recovered to the original length so as to disengage the pin from the retainer when the spring member is heated such that the door panel may be opened automatically in a fire.

Abstract: A door locking and unlocking safety mechanism comprising a push mechanism actuator structure to be carried by the door; a single rod operatively connected with the push mechanism to be displaced by operation of the push mechanism; door latch mechanism operable to latch and unlatch the door in response to movement of the single rod; and temperature response blocking structure associated with the latch mechanism to block operation of the latch to unlatch the door, in response to a predetermined increase in ambient temperature.

Abstract: Release mechanism for releasing a door-spring blocked by a blocking device, which mechanism comprises a temperature-sensitive control element for direct thermal actuation, by means of which the mechanism intervenes in the blocking device at a predetermined temperature of that element such that the door-spring is released. The release mechanism comprises for instance a rod guided for movement in longitudinal direction between a first end position and a second end position under a first bias in the direction to this first end position, and a control element comprising an SME material which at the predetermined temperature encloses the rod under a second bias greater than the first and in opposite direction thereto, which rod is coupled to a control member of the blocking device, which control member keeps the blocking device in operation in the first end position of the rod and renders the blocking device inoperative in the second end position of the rod.

Abstract: Disclosed is a door lock for locking a double-swinging type fire protection door. The door lock has a safety device controlled by a melting heat sensitive element to lock the spring bolt of the lock bolt in the locked position when the ambient temperature is sharply increased due to a fire.

Abstract: A latch assembly for a fire door having a pushpad for emergency exit is described. The pushpad is connected to a rod to transfer motion of the pushpad to the latch assembly. The latch assembly includes a platform attached to the fire door, a linkage assembly attached between the rod and a latch bolt, and a deadlock arm assembly attached to the platform. The deadlock arm assembly is movable between a first position to block movement of the linkage assembly and a second position to allow movement of the linkage assembly. A fire fuse assembly is also attached to the linkage assembly to move the deadlock arm assembly out of its first position blocking movement of the linkage assembly at normal room temperature.

Abstract: A lock for a door latch which includes a bolt moveable from a first position where the door is unlatched to a second position where the latch engages the door to hold the latch in the second position at selected temperatures.

Abstract: A link, used to allow retraction of the latchbolt against the bias of a spring, is formed of a fusible material to insure that, in the presence of intense heat, the link will melt and will no longer override a deadlocking pawl to allow the latchbolt to be withdrawn.

Abstract: An oven safety door latch has a pair of elongated latch arms pivotably connected to each other and to a base at a point intermediate their length. The arms project beyond the base and have end portions with opposed latching noses. A pawl is rotatably mounted on the base adjacent an end of the arms and has a blocking element engageable with the arms. A spring biases the latch arms and thereby the noses towards each other, and a stop element limits this movement of the noses towards each other. A thermally responsive element is operatively connected to the pawl to rotate it between a first position in which the blocking element is spaced from the arms, and a second position in which the blocking element is engaged with the end portions of the arms to limit their movement and thereby the movement of the noses away from each other to maintain the latch in engagement with the oven door.

Abstract: A lock mechanism including a latch assembly for being attached to a movable door member and for movement between an extended position in which the movable door member is locked in a closed position and a retracted position in which the movable door member is allowed to move between opened and closed positions. A holding assembly is included for normally holding the latch assembly in the retracted position. Intumescent material is included for forcing the latch assembly to the extended position if subjected to heat above a certain temperature.

Abstract: A safety seal for sterilizable containers that is closed by the temperature prevailing in the sterilizer. The closed seal then indicates the integrity of the container. The sealing mechanism in the illustrated embodiment is a pushbutton 100 that is subject to the force of a spring 102. The spring is made of a memory-retaining alloy that provides tension at a temperature above a transition temperature and forces the pushbutton into a locking state. The container can be opened once the pushbutton has been forced back, but the pushbutton cannot be returned to its locking position until it attains the transition temperature again.

Abstract: A fire-retardant pivoted door assembly with fire activated latching members includes a metal door frame having jambs and a header in which a fire-retardant door is mounted by a hinge assembly with a lower temperature resistance that the door and frame. Fire actuated latch bolt assemblies in the door are spaced vertically along the hinge side of the door, and include a housing providing an elongated cavity opening at the edge of the door. A latch bolt is slidably seated in the cavity and is biased towards the opening of the cavity. A fusible closure extends across the opening of the cavity and retains the latch bolt against the biasing pressure, and the hinge jamb has a spaced recess formed therein to receive the latch bolt upon melting of the fusible closure.

Abstract: A coupling device with a thermal interface occuring along a curved vertical surface is disclosed. One curved surface is on a cold pin extending from a "cold" object and the other curved surface is on a hot pin extending from a "hot" object. The cold pin is fixed and does not move while the hot pin is a flexible member and its movement towards the cold pin will bring the two curved surfaces together forming the coupling and the thermal interface. The actuator member is a shape-memory actuation wire which is attached between the hot pin and the hot object. By properly programming the actuation wire, heat from the hot object will cause the actuation wire to move the hot pin towards the cold pin forming an effective thermal interface. The shape-memory actuation wire is made from a shape-memory-effect alloy such as Nitinol.

Abstract: The invention provides a lock with a forward and reverse action bolt element and a lock cylinder which precedes the operating region of the bolt element into which the force for shifting the bolt element is to be introduced. The lock comprises an arresting element which can be fused at least locally by the effect of heat on the lock cylinder and which, after fusion, arrests the bolt element against reverse lock actuation.In an alternative embodiment, the lock may comprise a coupling between the operating region and a lock-actuating element spatially separated from it and protected by the lock cylinder, which coupling can be broken by fusion due to the effect of heat on the lock cylinder.

Abstract: A door lock apparatus includes a latch bolt which can be displaced from an operable position by actuating a door handle driver against the action of a biasing spring. A displaceable catch is provided for retaining the latch bolt in a retracted position. The catch is biased by a second spring into its catch position from which it can be displaced by an electromagnetic actuator, which in turn is connected to a wireless signal receiver. An alarm detector, remotely placed from the lock apparatus and connected to a wireless signal transmitter, is adapted to be activated when the detector detects a state of alarm, sending a signal which is detectable by the receiver at the lock apparatus for displacing the catch out of its catch position.

Abstract: Apparatus for rapid locking and delayed unlocking of the door closing mechanisms of machines such as washing machines with internal parts which are subject to inertial rotation. A sliding bar (15) is engaged by the hook (100) of the door-latch and is locked during the rotational part of the cycle by a pin (21) actuated by the mobile contact plate (8) of a microswitch through a rocker arm (6) moved by a bimetallic strip (2) suitably heated by a resistor electrically connected to the starting controls of the machine. The mobile contact plate (8) of the microswitch is subjected to the load of an eccentric ratchet (12) to control the insertion time and delayed opening of the door-lock. The bimetallic strip (2), heating resistor (5), and the rocker arm (6) rest one on another to assure that the curving and straightening times of the bimetallic strip (2) remain stable through time.

Abstract: A push-type and a pull-type door-latch opener capable of use with a plunger-type fusible pin operated fire-safety lock mechanism including a mounting plate, a horizontal pivoting rod attached to the plate, a vertical pivoting rod attached to the plate at a right angle to and adjacent the horizontal pivoting rod, a horizontal bell crank pivoted about the vertical rod and having a first arm projecting into the plane of the door for operating the door-latch and a second arm engaged by a portion of a door handle pivoted on the horizontal rod, and a torsion spring coaxial with the horizontal rod for biasing the door handle into a preselected position.

Abstract: A door interlock arrangement for an appliance such as a self-cleaning electric oven has an operating lever manually movable in a limited arc to move a door bolt into and out of door latching position and provide further motion to close the door very securely, and has a lock arranged in a novel cooperative relationship with an electrical interlock unit to permit certain appliance operations only when the door is latched and to permit opening of the door after the end of those appliance operations only when a selected appliance zone has cooled to a safe temperature.

Abstract: A fire-resistant container for magnetic media is constructed by mounting a base of thermal insulation material within a casing having an open face and by positioning on the base and securing to the base a body of thermal insulation material so as to define with the base a cavity which is open towards the open face of the casing. An inner container is positioned within the cavity so as to have an opening towards the open face of the casing and has an inner wall defining a storage cavity and an outer wall which defines a chamber filled with heat absorbing material between the inner and outer walls. A storage drawer is inserted into the storage cavity and has attached thereto a container located on that side of the drawer adjacent to the opening, the container being filled with a heat absorbing material. A layer of thermal insulation material is positioned on that side of the container remote from the drawer and a facing is located on that side of the layer of insulation material remote from the container.

Abstract: A fire rated electrically operable strike in which a pivotable keeper is prevented from pivoting by a locking member which is spring biased into a position in which pivoting of the keeper is prevented until the locking member is moved from its normal, locking position by the electrical energization of a solenoid which actuates an armature connected to the locking member. The locking member has a recess into which a spring biased ball extends when the locking member is in its locking position. The materials from which the ball and its mounting are made and the relative dimensions thereof are selected so that when the temperature to which the strike is subjected is greater than normal, such as by reason of a fire, but less than a temperature at which the locking member biasing spring is ineffective, the ball expands and the mounting for the ball changes size so that the ball cannot retract from the recess in the locking member, and the locking member is held in its keeper locking position.

Abstract: A door lock structure includes a frame and a latch bolt carried by the frame for movement between retracted and advanced positions relative to a jamb. The bolt in its retracted position allows the door to open and when its in its advanced position blocks the closed door from opening. A first heat-fusible spring carried by the frame urges the bolt toward the advanced position. A lever pivotally carried by the bolt pivots between a first bolt blocking position and a second bolt freeing position. The lever has a second heat fusible spring carried by the bolt and acting on the lever for urging the lever toward the first bolt blocking position. The frame carries an actuator for pivoting the lever into the second position allowing movement of the bolt toward the retracted position. The lever also has a counterweight on the lever for keeping the lever in the first position to block retraction of the bolt in the event that the first and second springs melt.

Abstract: A self-cleaning over door latching mechanism is provided with a locking arrangement responsive to the oven cavity temperature, which includes a locking pin moved by a snap action bimetal member mounted in thermal communication with an oven cavity wall. The bimetal member moves the locking pin to a locking position when the temperature sensed by the bimetal rises above the locking temperature. In its locked position the locking pin prevents the opening of the latch until the temperature in the oven cavity falls below the locking temperature. In its locked position the locking pin also actuates a lock switch electrically connected in parallel with a thermal limit switch. The thermal limit switch provides over temperature protection for the cavity when operating in the normal cooking modes. When actuated, the lock switch shunts the limit switch thereby enabling the temperature in the cavity to rise to the self-clean range.

Abstract: A door retention assembly 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, and there being a strike carried by one of the elements. The assembly includes:(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 a control to control movement of the latch into and out of latching relation with the strike. A heat fusible part, when fused, renders the control inoperable to effect movement of the latch out of latching relation with the strike.

Abstract: A locking mechanism for securing together two separable pieces, such as two components of a spacecraft during launch. An elongated rod of heat contractible material provides a single active member which changes from a locking length to a contracted length upon application of sufficient heat to raise the temperature of the rod from below to above its transition temperature. Mounting and housing structures are provided for mounting and heating this transducer rod and an apertured member or recessed stop is provided for engaging a projecting portion thereof. Heating may be provided by redundant, electrically actuated heating coils surrounding a major portion of the rod length. At least a major portion of the transducer rod may be made of 55-Nitinol.

Abstract: An exit device primarily designed for outwardly opening doors comprises a rigid plate member having mounted thereon a latch-bolt assembly anchored to a door member and a strike assembly mounted on a door frame member in operative association with the latch-bolt assembly, wherein the plate member includes projections positioned to be on each side of the latch bolt of the latch-bolt assembly, and wherein the strike assembly includes recesses for receiving such projections. The recesses in the strike assembly are configured in relation to the projections to allow limited vertical movement of the projections within the recesses. When the device is subjected to a major force such as in a fire the projections will restrict linear growth of the frame member in the latch area by engagement of the projections, with the walls of the recesses thereby preventing excessive strain from occurring on the latch bolt which can lead to disengagement of a latch bolt from the strike.

Abstract: A door latch bolt spring-biased to projected position and retracted by a lever or other unbalanced handle is provided with a blocker plate loosely mounted on the rear face of the bolt and held in nonblocking position by a fusible pin or other heat-sensitive element. In case of fire, when elevated temperature may weaken the biasing spring and allow the unbalanced handle to exert retracting force on the latch, the heat-sensitive element releases the blocker plate and allows it to drop to an operative position where it will move against a stop to block retraction of the bolt. The plate is movable in either direction on the bolt so as to be operative on either hand or door. The tailpiece of the latch bolt carries means for mounting a reaction plate for the biasing spring and the blocker plate is loosely received between such plate and the rear face of the latch bolt. The reaction plate can be omitted when the blocker is not used, but can be supplied at any stage of manufacture or in the field when desired.

Abstract: A door locking device for an appliance such as a washing machine has a rotatable lock lever actuated to engage a latch carried by the door to hold the door in a closed position. The lock lever is actuated by a bimetallic element which is adapted to be connected in series with the drive motor when the washing machine is in the spin condition so that the electric current passing through the drive motor passes through the bimetallic element and the resulting heating and deflection of the bimetallic element actuates the lock lever. The unit also carries an interlock switch actuated by the latch mechanism to prevent operation when the door is open. A shunt switch is provided to close electrical contacts when the bimetallic element and lock lever are deflected to the locked position to shunt current past the bimetallic member to prevent further heating and to insure a substantially constant unlock time.

Abstract: There is described a fire-break door comprising a swivelling leaf provided with at least one lock with draw-bolt which can be controlled by an operating member, said leaf cooperating with a door-closer allowing to swing said leaf back automatically to the closed position thereof, in which means are provided on the one hand to retain the lock bolt in a recessed or withdrawn position when the door leaf lies in closed position, and on the other hand to let the bolt be released and enter the keeper of the lock with an abnormal rise in the temperature adjacent the door.

Abstract: A crash bar door locking device is provided, suited for mounting on the inside of a swinging door. The crash bar is mounted horizontally across the door providing ready access by movement in the outside direction. The crash bar activates a pivotal lever which causes a latch bolt to rotate inwardly and disengage from a door strike. The pivotal lever provides a deadbolt feature by preventing the rotation of the latch bolt. A release is incorporated in the latch bolt and allows the latch bolt to rotate when the release engages the door strike as the door closes. An additional unlocking mechanism may be provided for retracting the latch bolt from the outside of the door independently of the crossbar. A firelocking mechanism may be incorporated in the latch bolt to secure the latch bolt when a fire occurs. Two pins with a spring between them are retained by fusible plugs at either end of a bore in the latch bolt, so that the latch bolt operates as a normal lock on the door.

Abstract: Delayed release locking control device, particularly for doors of washing machines and the like, containing inside a case a self-regulating resistive wafer heater of a material having a positive temperature coefficient (PTC) of resistance, a snap-acting bimetallic element connected to a latch or locking member, and terminals which carry electrical current to the PTC wafer heater, wherein the bimetallic element is arranged so means transform the linear snap like movement of an end of the bimetallic element into a rotary movement of the latch mounted on the case to cause it to rotate 90.degree. from a resting position into an operating position when the bimetallic element, selectively heated by the said PTC wafer, abruptly reverses its curvature upon reaching the actuating temperature of reversal and to cause the said latch to return to the resting position when the bimetallic element cools down again to below a reset temperature of reversal and snaps back to its normal curvature.

Abstract: A window guard is hinged to a wall member and is releasably secured thereto by a latch means which interconnects the wall member and the window guard and is operated by a cable which extends to a weighted member held by a low melting point link. When the link melts or the cable is pulled the weighted member drops to release the latch means. Also, a drop latch is guided in a stile of the window guard and detent means operable from an opposite side of the wall member releases the drop latch from latching engagement with latch catch means on the wall member.

Abstract: A door control mechanism for use in conjunction with a pair of swinging doors to control latching. The mechanism comprises a first stamped metal part adapted to be fixedly mounted on the door. This part comprises a first track portion and a second track portion. A second stamped metal part comprises a slide portion which slidably engages one track portion of the first metal part. An actuating mechanism is arranged on the second track portion of the first stamped metal part and has an operative coupling with the second stamped metal part. The second stamped metal part is adapted to be connected to a latch bolt. When the actuating mechanism is operated, the second stamped metal part is selectively positioned along the first track portion of the first stamped metal part with the bolt being positioned accordingly.

Abstract: Exit device has auxiliary bolt which when held in by door strike permits a blocking leg to prevent unauthorized forced retraction of main latch bolt. Normal operation of device by panic bar pivots blocking leg out of the way and then retracts main latch bolt.

Abstract: A device for indicating whether a container has been both exposed to a critical temperature and not subsequently opened which includes a housing, a temperature-sensitive member which assumes a first position and a second position within the housing, and a rigid member connected to the temperature sensitive member which moves into view when the temperature sensitive member assumes its second position upon exposure to a critical temperature, and moves out of view when the container is opened.

Abstract: A door latch mechanism for controllably securing a door, the latch mechanism of the type having a spindle and operating handles, comprises a fusible connecting member rigidly attaching the handle and spindle at room temperature, the fusible connecting member melting at elevated temperatures to permit relative rotation of the handle and spindle. The handle is mounted using a connecting member which is attached to the latch trim using a screwless connection. This is particularly applicable to latches using lever handles in that a positive positioning mechanism holds the handles at their selected positions, regardless of wear and age.

Abstract: A flush bolt mechanism adapted to be mounted at the vertical edge of the inactive door of a pair of hinged doors. Means are provided to prevent damage to the mechanism due to misalignment of the bolt and the strike plate. All translational motion of the mechanism substantially takes place along a single axis except for the motion of activation.

Abstract: The invention comprises a latching and unlatching device for use on a door, or bulkhead, or the like, which device has a blocking plate for internally obstructing the latch to prevent its retraction, thereby to prevent the opening of the door. The blocking plate is internally secured in place, in an intermediate slidable position, where it does not obstruct the latch, by a low melting point cover. In the presence of excessive heat, as on the occurence of fire, the cover melts; this allows the blocking plate to slide to another, operative position in which it prevents the retraction of the latch and, consequently, the unlatching of the device. The method comprises the steps to be undertaken to modify an off-the-shelf latching and unlatching device to insure that it will be held securely latched in the presence of fire or excessive heat, and the kit sets forth the structure elements required for the aforesaid modification of off-the-shelf, latching and unlatching devices.

Abstract: In the preferred embodiment depicted, the invention comprises a limb, having a depending lug, fixed to a door. The lug makes a close clearance, near engagement with a socket-retainer fixed to a door-interfacing mullion. The upper end of the mullion is foreshortened, and addressed to a free space; it is slidably engaged with an internal socket. Accordingly, in the event of fire, the mullion may freely extend vertically, due to the heat. Such free extension causes the socket-retainer, and the depending lug, mutually to engage. By this arrangement, the door is secured closed, on the exposure to severe heat, even if the normal latching and/or locking device therefor comes loose or disengaged. The method comprehends fixing the mullion at one end, securing it against angular movement, exposing the other end to a free space, and mounting to the closure and mullion locking components which come into engagement only in response to thermal extension of the mullion.

Abstract: A product monitoring device including a releasable locking device adapted to be secured to a product and actuatable between locked and unlocked positions. The locking device consists of a pair of movable members, one of which mounts a bimetallic member consisting of bimetal elements having different temperature coefficients of expansion, the bimetal elements being separated by an insulator. The locking device includes a detent cooperatively associated with the bimetallic member to maintain the members in a locked position. The device uses an electrifiable key for heating the bimetallic elements to effect displacement thereof relative to the detent to facilitate movement of the members to an unlocked position. The device incorporates structural features which increase strength in operation, and further serve to make unauthorized opening and/or breakage of portions, with the intent of permitting separation from an article to which attached, more difficult.

Abstract: A fluid pressure motor having a normally used internal electrical heating element which vaporizes internal fluid to actuate the motor. The motor further includes means in heat transfer proximity to the outside of the motor which can be caused to convert its stored energy to sufficient heat to actuate the motor.

Abstract: Push rod of panic-type latching device contains a fusible section which melts in the event of a hot fire so that the temperature will not cause elongation of push rod to disengage upper door latch.

Abstract: A safety anchor latch device for a metallic latch strike including a plastic latch and a metallic spring member having positive position retaining means and positive strike gripping means which at normal operating temperatures are inoperative and supported by the elements of said plastic latch in space relation to a supporting work structure and the metallic latch strike respectively but which positively engages and retains same when said plastic latch is destroyed by abnormally elevated temperatures.

Abstract: A novel locking clip is disclosed for use with either fire or smoke dampers, which locking clip normally does not interfere with the operation of those dampers but, which under activation conditions, allows the blades of the damper to move into the desired position, but effectively prevents the blades from moving out of that position until fire conditions have passed.

Abstract: A novel telescoping heat responsive releasing device is described wherein a mounting member on which a bimetallic means is mounted slidingly engages a pawl member which is movable between a first position in which the pawl member is capable of being restained by the aforementioned bimetallic means, and an actuating position wherein associated apparatus connected to said releasing device may assume the desired heat responsive posture. Various alternate embodiments are illustrated wherein a plurality of bimetallic elements are utilized to engage the pawl member, wherein a bimetallic element is additionally actuated mechanically or electrically, and wherein various pawl and mounting member configurations are illustrated.

Abstract: A door closure apparatus is provided for automatically closing a bifold door of a storage cabinet for combustible materials in the event of elevated temperatures. A guide assembly hingedly mounted on the free end of the folding door includes guide fingers which ride along a guide path in a channel guide track at the top of the cabinet. At one end of the track there is mounted a bracket slidably carrying a latch member movable between a latching condition in the guide path and a release condition out of the guide path. The latch member is normally held in its latching condition by a spring and fusible link combination which override a smaller spring urging the latch member toward its release condition. Upon melting of the fusible link the latch member is moved to its release condition by the smaller spring. The latch member is shaped to permit the guide member to cam past it as the door moves to its open position but prevents return movement of the guide member to hold the door in its open position.

Abstract: A catch mechanism for installation in a door frame to cooperate with a door lock on a fire door. The mechanism includes a catch member pivotable between an operative position in which to serve as a door catch and an inoperative position to enable release of the door no matter what the condition of the door lock. The mechanism includes a heat responsive locking device which locks the catch member in its catch position in the event of a fire generating high temperatures. The locking device may comprise a biased locking plunger mounted in a cavity within the catch member and normally held in a retracted position by a heat fusible metal plug but extendible on melting of the plug to engage the catch body and so lock the catch member.