US3056122A - Fire alarm system - Google Patents

Description

p 1962 H. o. MOORE I 3,056,122

FIRE ALARM SYSTEM Filed June 10. 1959 2 Sheets-Sheet 1 HARRY O- M00125 INVENTOR. 16 23 sYiJmp eflfi -udf I l 2 I ATTORNEYS Sept. 25, 1962 H. o. MOORE FIRE ALARM SYSTEM Filed June 10, 1959 2 Sheets-Sheet 2 BY ,fi 4

ATTORNEY United States Patent M 3,056,122 FIRE ALARM SYSTEM Harry 0. Moore, 2921 Rozzells Ferry Road, Charlotte, N. C. Filed June 10, 1959, Ser. No. 819,356 8 Claims. (Cl. 340-232) This invention relates generally to improvements in fire alarm systems, and more particularly to improvements in fire alarm systems of the type suitable for use in a dwelling structure or home.

Although fires annually cause extensive losses of life and property so as to create a desire for providing a reliable fire alarm system in dwelling structures, such as houses, apartments, etc., this desire has largely remained unsatisfied mainly because of the expenses involved in installing conventional commercial fire alarm systems in homes. Simplified fire alarm systems employing highly combustible materials as fuses to set off fire alarm devices have been developed for use in the home, but have not been favorably received by the home-owner, possibly because of the hazards inherently presented through the use of such combustible fuses which themselves may be the cause of fires. A common failing in these conventional home fire alarm systems exists in their relative lack of sensitivity to an abrupt increase in heat, a factor which allows a fire to gain a good head-way before the alarm is actuated to alert the occupant of the dwelling structure to the presence of the fire. In such instances, attempts by an occupant to put out the fire are futile or at least greatly hampered when the fire has been allowed to develop in intensity and to rage uncontrolled.

Perhaps the largest incidence of destruction of life and property by fires in the home occurs during the fall and winter months when colder temperatures require the operation of a furnace for heating the home. This is partly explainable because of the consumption of a combustible fuel by the furnace when in operation. The fire upon reaching the fuel flowing into an operating furnace quickly develops in intensity as it consumes the fuel and may become virtually uncontrollable. In addition, the heat from the fire on the furnace may create a highly explosive condition because of the resulting vaporization and/or expansion of the fuel flowing into the furnace.

It is an object of this invention to provide an improved fire alarm system utilizing an alarm device, which may be in the form of a bell, interposed in an electrical alarm circuit having a normally open switch therein, and the switch being held in open position by a taut strand of thermoplastic material extending throughout a room or rooms in the building structure. The thermoplastic strand is highly sensitive to an abrupt increase in heat so as to part upon a fire being started to release the switch allowing it 'to close and complete the alarm circuit for actuating the alarm device.

It is another object of this invention to provide an improved fire alarm system cooperating with the electrical circuit for operating a furnace in a dwelling structure, wherein the alarm device in the fire alarm system is actuated in response to an abrupt increase in heat caused by the starting of a fire while the electrical circuit for the furnace is broken to shut olf the furnace and reduce the dangers which would be inherently presented by the continued flow of fuel to the furnace if the furnace remained in operation.

It is another object of this invention to provide in a fire alarm system having an electrical alarm circuit with an alarm device disposed therein and switch means in the alarm circuit, a strand of thermoplastic material normally holding the switch means open and being attached to a furnace damper to prevent the damper from closing the 3,056,122 Patented Sept. 25, 1962 air intake opening of the furnace. Upon a fire breaking out in the vicinity of the thermoplastic strand, the thermoplastic strand will part allowing the switch means to close the alarm circuit and the damper to close the air intake opening of the furnace, thereby actuating the alarm device and eventually causing the fire in the furnace to be smothered by blocking the air intake opening.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings, in which-- FIGURE 1 is a schematic perspective view illustrating the fire alarm system embodying the present invention as being installed in a room, such as a basement or cellar in a dwelling structure;

FIGURE 2 is a diagrammatic view illustrating the wiring of the fire alarm system shown in FIGURE 1 with the back wall of the switch removed;

FIGURE 3 is a sectional view of the switch utilized in the fire alarm system, taken substantially along the line 3-3 in FIGURE 2;

FIGURE 4 is an elevational view of a furnace, parts thereof being shown in phantom lines for purposes of clarity, illustrating a modified form of fire alarm system associated therewith;

FIGURE 5 is a fragmentary horizontal sectional View taken along the line 55 in FIGURE 4;

FIGURE 6 is an enlarged fragmentary vertical sectional view, taken along line 66 in FIGURE 4;

FIGURE 7 is an enlarged horizontal sectional view of the switch means utilized in the modified fire alarm system, taken along line 77 in FIGURE 4; and

FIGURE 8 is a diagrammatic view illustrating the wiring of the modified fire alarm system and showing the switch means in vertical section, as taken along line 88 in FIGURE 7.

Referring more specifically to the drawings and to FIGURE 2 particularly, there is illustrated means for connecting the fire alarm system to the existing source of electrical current in a dwelling structure, this means being shown in the form of an electrical connector plug 10. From the plug 10, a pair of electrical conductors or wires 11, 12 extend to a bell transformer 13 to supply electrical current thereto. The bell transformer 13 is of a conventional step-down type, designed to supply six (6) volts to an alarm device 14 through wires 15, 16 extending between the bell transformer 13 and the alarm device 14-.

The alarm device 14 preferably takes the form of a bell, as shown, the bell preferably being installed in a room likely to be inhabited during the major portion of a day. It is contemplated that the fire alarm bell 14 may also be the front door bell of the dwelling structure or could be installed at a convenient outside location so as to warn not only the inhabitants of the dwelling structure but also their neighbors in the event that the dwelling structure is unoccupied at the time when a fire breaks out. A light signal (not shown) may be incorporated with the alarm bell 14 to give a visual alarm, if desired.

A switch means 20 is interposed in one of the wires 15, 16 extending between the transformer 13 and the alarm device 14, FIGURE 2 illustrating the switch means 20 as being interposed in the wire 16. The details and functioning of the switch means 20 will be subsequently described.

The electrical plug 10* also includes a second pair of wires 21, 22 extending therefrom, the wires 21, 22 forming an electrical circuit for operating the electric motive means, hereinafter referred to as a motor 23, of a furnace 24. It will be observed that the Wire 21 leads directly from the plug 10 to one terminal of the motor 23, while the wire 22 is interrupted by the disposition of the switch 3 means 20 therein so as to form an indirect connection between the plug and the other terminal of the motor 23.

The details of the switch assembly 20* will now be described. The switch means 20 is of a double-throw type and comprises a flanged back wall 24 which is adapted to be aflixed to a wall of the dwelling structure by suitable means and a casing or switch housing 25 having side walls and top and bottom walls frictionally received by the flanged back wall 24 to enclose the operating parts of the switch means 20. A pair of spaced switch contact members 26, 27 are suitably mounted within the confines of the switch housing 25 on the front wall thereof. It will be observed that a layer of insulation material, such as rubber, is sandwiched between each of the switch contact members 26, 27 and the wall surface of the switch housing 25 on which they are mounted as a precautionary measure to prevent the switch housing 25 from becoming electrified. The spaced switch contact members 26, 27 may take any desirable form, being L- shaped as shown to present spaced parallel legs or contacts 30, 31 extending away from the front wall of the switch housing 25.

A switch arm or lever 32 is mounted in the switch housing 25 for pivotal movement about one of its ends. The opposite end of lever 32 extends between the contacts 30, 31 of the switch contact members 26, 27, respectively. The pivotal mounting of the switch lever 32 may be accomplished in any desired manner, such as by mounting one end of the switch lever 32 about the shank of a screw 33 protruding from the front wall within the interior of the switch housing 25, the shank of the screw 33 being loosely received in a bore provided in the end of switch lever 32, as shown in FIGURE 2. The switch lever 32 preferably includes an integral leg 34 extending transversely from the end thereof loosely receiving the screw 33. It will be observed that a counterweight 35 is provided on the end of the leg 34 remote from the pivotally mounted end of switch lever 32 for a purpose to be subsequently described.

A pair of contact plates 36, 37 are provided on opposite sides of the switch lever 32 at locations in alinement with the contacts 30, 31, respectively. The switch lever 32 is insulated from the contact plates 36, 37 by a suitable layer of insulation material, such as rubber, sandwiched between each of the contact plates 36, 37 and the corresponding side of the switch lever 32. A resilient means in the form of a coiled compression spring 40 biases the switch lever 32 about its pivot point in a clockwise direction, as viewed in FIGURE 2. The coiled spring 40 is seated between one of the side walls of the switch housing 25 and a medial position on the switch lever 32, cup- like elements 41, 42 being secured to the switch housing 25 and the switch lever 32, respectively, to receive opposite ends of the coiled compression spring 40.

It will be observed that each of the contacts 30, 31 and the plates 36, 37 is provided with a single terminal thereon for connection to an electrical conductor or wire in the fire alarm system. In this connection, contact 30 and plate 36 are connected to the adjacent terminal portions of the segments comprising wire 22 which extends between the plug 10 and the motor 23 for the furnace 24, while contact 31 and plate 37 are connected to the adjacent terminal portions of the segments comprising wire 16 which extends between the bell transformer 13 and the fire alarm device 14. It will be apparent, therefore, that engagement between the contact 30 and plate 36 will complete the electrical circuit through the motor 23 of the furnace 24 to supply current to the motor for operating the furnace, while engagement between the contact 31 and plate 37 will complete the electrical alarm circuit to actuate the alarm device 14 therein. The switch lever 32 is movable about its pivot point so as to effect alternative engagement between the two sets of switch elements 30, 36 and 31, 37, each set comprising a contact and a plate, respectively. From the foregoing, it will be understood that the electrical circuit for the motor 23 of the furnace 24 and the electrical alarm circuit for the fire alarm device 14 are never completed at the same time. Normally, the switch lever 32 will be held in a position wherein the contact plate 36 thereon engages contact 30 to complete the electrical circuit through the motor 23 of furnace 24, this being accomplished by a heat-fusible strand 43 of thermoplastic material, such as nylon or polyethylene, one end of which is attached to the end of the witch lever 32 opposite from the pivotally mounted end in a suitable manner. The thermoplastic strand 43 is disposed about a room in a dwelling structure which is infrequently occupied, such as a basement, cellar or attic, FIGURE 1 illustrating the strand 43 as being threaded through a plurality of eye-bolts 44 depending from the beams 45 of a basement ceiling. The eyebolts 44 are preferably arranged to distribute the thermoplastic strand 43 in such a manner as to cover a large area of the room. A weight 46, such as a sandbag or the like, is attached to the other end of the thermoplastic strand 43 to maintain it in a taut position so as to pull the switch lever 32 in a counter-clockwise direction, thereby compressing spring 40 and effecting engagement between the contact 30 and plate 36.

The thermoplastic strand 43 is very susceptible to an abrupt increase of heat and will part at a point or points therealong upon a fire being started in the vicinity thereof. In this respect, tests were conducted with strands of nylon and high-tenacity polyethylene as compared to a strand of cotton, wherein the strands were held in a taut condition above the flame from a match. The nylon and polyethylene strands readily parted, but the cotton strand remained intact and did not part until it was lowered relative to the flame. Because of the high tensile strength of nylon and polyethylene strands as contrasted to that of a cotton strand, a nylon or polyethylene strand when employed as the thermoplastic strand 43 in the present invention can be of a filamentous nature, while a cotton strand would necessarily be somewhat bulky in order to withstand the tension placed thereon without breaking. The nylon and polyethylene strands thus exhibited high heat sensitivity and high tensile strength. These factors coupled together in the strand 43 employed in the fire alarm system result in a marked degree of sensitivity of the fire alarm system to the presence of a fire.

A single break in the thermoplastic strand 43 relieves the switch lever 32 from the pull exerted thereon by the weight 46, whereupon the compressed coil spring 40 is permitted to expand while the counter-weight 35 tends to fall downwardly. The conjoint action of the coil spring 40 and the counter-weight 35 causes the switch lever 32 to pivot in a clockwise direction to effect engagement 'between the contact 31 and plate 37, while breaking the engagement between the contact 30 and plate 36. The provision of the counter-weight 35 on the leg 34 of the switch lever 32 insures that the switch lever 32 will move in a clockwise direction upon a parting of the thermoplastic strand 43, even though the coil spring 40 may have become permanently deformed or crystallized in its compressed state due to remaining in its compressed state over a long period of time.

Upon clockwise movement of the switch lever 32 being effected as described herein, the electrical alarm circuit is completed by the engagement between the contact 31 and plate 37 to actuate the alarm device 14 which warns of the presence of a fire. At the same time, the electrical circuit through the motor 23 of the furnace 24 is broken by the disengagement of the contact 30 and plate 36 to stop the operation of the furnace 24 and accordingly eliminate the danger presented by the continuous flow of fuel into the furnace 24 if the furnace 24 remained in operation.

Referring now more particularly to FIGURES 4-8, inclusive, a modified form of the fire alarm system is shown- Reference characters with the prime notation added will be used to designate elements similar to those found in the fire alarm system disclosed in FIGURES 1-3, inclusive. Thus, FIGURE 8 shows an electrical connector plug 10 for connecting the modified fire alarm system to the existing source of electrical current in the dwelling structure. From the plug 10', a pair of electrical conductors or wires 50, 51 extend to a bell transformer 13' to supply electrical current thereto, the bell transformer 13' being for the same purpose described in connection with bell transformer 13 of FIGURES 1-3, inclusive, that isto supply six (6) volts to an alarm device 14 through wires 52, 53. A switch means is interposed in the wire 53 extending between the transformer 13 and the alarm device 14'.

It will be observed that the wires 50, 51 across which the primary coil of the 'bell transformer 13 is connected form an electrical circuit for operating the electric motive means, hereinafter referred to as motor 23', of a furnace 24'.. The wire 50 leads directly from the plug 10' to one terminal of the motor 23', while the wire 51 is interrupted by the disposition of the switch means 20' therein so as to form an indirect connection between the plug 10 and the other terminal of the motor 23.

The switch means 20' in the modified fire alarm system comprises a switch housing or casing 55 adapted to be afiixed to an outer wall surface of the furnace 24' and having a cover or lid 56 received thereon so as to enclose the operating components of the switch means 20' within the switch housing 55. Within the confines of the switch housing 55, there is a first switch unit 57 which comprises a closed tube or vial 60 having one end loosely mounted about a pin 61 attached to a bracket member 62 (FIG- URE 7). The bracket member 62 is secured to the back wall of the switch housing 55. The vial 60 is free to pivot about the pin 61. The terminal portions of the segments comprising wire 51 extend into the vial 60 in spaced apart relationship to provide a break in the electrical circuit for the motor 23. A globule of mercury M is contained within the vial 60 and is adapted to bridge the gap between the adjacent terminal ends of the segments comprising wire 51 to complete the electrical circuit through the motor 23 for the furnace 24'. The first switch unit 57, hereinafter termed a mercury switch, isnormally maintained in the position shown in-FIGURE 8, wherein the mercury globule M bridges the gap between the adjacent terminal ends of the segments comprising wire 51 by means to be subsequently described.

A second switch unit 66 is also contained within the switch housing 55, the second switch unit 66 being disposed in the wire 53 forming part of the electrical alarm circuit through the alarm device 14". As shown, the second switch unit 66 [is of the push-button type and comprises a switch arm 67 having a contact 68 on its lower surface and a push-button 69 on its upper surface, the switch arm 67 being mounted in the switch housing 55 for pivotal movement about its end remote from the contact 68. A stationary switch element 70 having a contact 71 thereon opposed to the contact 68 on the switch arm 67 is mounted in spaced relationship with respect to the switch arm 67; Resilient means in the form of a spring 72 is interposed between the pivotal switch arm 67 and the stationary switch element 70 to normally maintain the contacts 68, 71 carried thereby in spaced apart relationship. It will be observed that the pivotal switch arm 67 is connected'to the terminal portion of one segment of wire 53, while the stationary switch element 70 is connected to the terminal portion of the other segment of Wire 53.

The switch means 20" is adapted to be interposed in a suitably insulated tubular member 74 which extends vertically along an outer wall surface of the furnace 24'. The tubular member 74 receives one terminal portion of a thermoplastic strand 43' which is intended to be disposed throughout a room or rooms of the dwelling 6 structure in a manner similar to that disclosed in FIGURE 1. It will be observed that the portion of the thermoplastic strand 43' in the tubular member 74 also extends through the switch housing 55, suitable openings being provided in the switch housing 55 for that purpose, and is attached to a damper element 75 for the air intake opening 76 of the furnace 24.

The damper element 75 is mounted for slidable movement along the outer wall surface of the furnace 24 for opening and closing the air intake opening 75 of the furnace 24. In this connection, a pair of spaced angleiron brackets 77 extending vertically along opposite sides of the air intake opening 75 may be aflixed to the outer wall surface of the furnace 24 to provide oppositely disposed slots or trackways for slidably receiving the side edges of the damper element 75. In normal operation, the damper element 75 is held in the position shown in FIGURE 6 by the thermoplastic strand 43' under the pull of a weight (not shown), such as the weight 46 shown in FIGURE 1, thereby uncovering the air intake opening 76 to permit air to be drawn into the furnace 24' for allowing proper combustion of the fuel being burned thereby.

It will be observed in FIGURE 8 that the thermoplastic strand 43 is provided with a collar member 80 of rigid material securely afiixed therearound and located within the switch housing 55. A stop means in the form of a pin 81 extends forwardly from the back wall of the switch housing 55. The mercury switch 57 includes an aperture 82 through the vial 60, the aperture 82 being located in the end thereof remote from the pivotally mounted end. The modified fire alarm system disclosed in FIGURES 4-8, inclusive, is cocked or readied for operation by passing the thermoplastic strand 43 through the aperture 82, in the vial '60 of the mercury switch 57 so as to dispose the collar member'St) on the thermoplastic strand 43 below the vial 611', while the pin 81 is disposed above the vial 60. The thermoplastic strand 43' is maintained in a tautcondition by a weight (not shown), such as the weight 46 shown in FIGURE 1, which pulls the collar member 80 upwardly against the vial 66 of the mercury switch 57 to pivot the vial 60 in a counter-clockwise direction until the vial abuts the pin 81. At the same time, the damper element 75 is drawn upwardly in the angle-iron brackets 77 to uncover the air intake opening 76 of the furnace 24'. The men: cury globule M accordingly shifts within the vial 60 to a position wherein it spans the gap between the adjacent terminal portions of the segments comprising wire 51 to complete the electrical circuit through the motor 23 for the furnace 24'. When the mercury switch 57 is in closed position, as shown in FIGURE 8, the push-button switch 66 is open and thereby holds the electrical alarm circuit through the alarm device 14 open because of the interruption in the wire 53 extending between the bell transformer 13' and the alarm device 14'.

Upon a fire breaking out in the vicinity of the thermoplastic strand 43, the strand 43' parts at a point or points therealong to release the upward pulling force of the collar member 80 on the switch 57. When the vial 60 of the mercury switch 57 is no longer drawn upwardly against the retaining pin 31 by the collar member 80, it pivots downwardly about pin 61 in a clockwise direction to cause the mercury globule M to shift its position therein which breaks the circuit through the motor 23' for the furnace 24'. The vial 60 strikes the button 69 on the pivotal switch arm 67 and forces the switch arm 67 downwardly in a clockwise direction against the biasing force of spring 72 to a position wherein the contact68 on the switch arm 67 engages the opposed contact 71 on the stationary switch element to close the electrical alarm circuit for actuating the alarm device 14'. Meanwhile, the parting of the thermoplastic strand 43' also releases the damper element which slides downwardly in the angle-iron brackets 77 to close the air intake opening 76 of the furnace 24.

In effect, therefore, the parting of the thermoplastic strand 43 by the presence of a fire in the room in which the thermoplastic strand 43' is located causes three separate safeguards in the modified fire alarm system to be actuated: (1) The electrical alarm circuit itself is completed to sound the alarm device 14' for warning occupants of the dwelling structure of the fire; (2) The electrical circuit through the motor 23 for the furnace 24 is broken, thereby shutting ofi the furnace 24'; and (3) the air intake opening 76 for the furnace 24 is closed by the damper element 75 which will eventually result in the fire within the furnace 24' being smothered to stop the operation of the furnace 24'. The shutting off of the furnace 24' whenever a fire breaks out in a room of the dwelling structure eliminates the hazard inherently incident upon continued operation of the furnace 24- by a constant flow of combustible fuel thereinto. It will be understood that such control of the furnace 24- insures that a fire which has broken out in the dwelling structure will not be fed by fuel flowing into the furnace 24', nor will the fire within the furnace 24' be permitted to escape its confines.

There have been disclosed improved fire alarm systems of a type suitable for use in a dwelling structure, the fire alarm systems being highly sensitive and accurate in operation, while relatively inexpensive in cost and free from maintenance.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

I claim:

1. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said electrical alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit, said switch means comprising a housing, a switch lever pivotally mounted in said housing and having contact plates on opposite sides thereof electrically connected in said furnace circuit and said alarm circuit respectively, and a pair of spaced apart contacts fixed in said housing on opposite sides of said switch lever in alinement with said contact plates carried thereon, one of said fixed contacts being disposed in said furnace circuit and the other in said alarm circuit, and a heatfusible strand attached to said switch lever and holding said switch lever in a position wherein said plate thereon and said fixed contact in the furnace circuit are in engagement for closing said furnace circuit and opening said alarm circuit, and means to pivot said switch lever to a position wherein said plate thereon and said fixed contact in the alarm circuit are in engagement for opening said furnace circuit and closing said alarm circuit in response to a parting of said strand for shutting off the furnace and actuating said alarm device.

2. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said electrical alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit, said switch means comprising a housing, a switch lever pivotally mounted in said housing and having contact plates on opposite sides thereof electrically connected in said furnace circuit and said alarm circuit respectively, and a pair of spaced apart contacts fixed in said housing on opposite sides of said switch lever in alinement with said contact plates carried thereon, one of said fixed contacts being disposed in said furnace circuit and the other in said alarm circuit, and a heatfusible strand attached to said switch lever and holding said switch lever in a position wherein said plate thereon and said fixed contact in the furnace circuit are in engagement for closing said furnace circuit and opening said alarm circuit, and a compression spring seated between said switch lever and said housing, said spring expanding to pivot said switch lever to a position wherein said plate thereon and said fixed contact in the alarm circuit are in engagement for opening said furnace circuit and closing said alarm circuit in response to a parting of said strand for shutting off the furnace and actuating said alarm device.

*3. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said alarm circuit, switch means interposed in said alarm circuit and operable to close said alarm circuit, a heat-fusible strand attached to said switch means and holding said switch means in a position opening said alarm circuit, a furnace having an air intake opening, a damper mounted on said furnace for movement between positions opening and closing the air intake opening, said strand being secured to the damper to normally restrain said damper in a position opening the air intake opening, said switch means being movable to a position closing said alarm circuit and said damper being movable to a position closing the air intake opening in said furnace in response to a parting of said strand for actuating said alarm device and stopping the intake of air by the furnace.

4. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said alarm circuit, switch means interposed in said alarm circuit and operable to close said alarm circuit, a heat-fusible strand attached to said switch means, means maintaining said strand in a pre-arranged manner extending over a wide area, and means stretching said strand taut for holding said switch means in a position opening said alarm circuit, a furnace having an air intake opening above which a damper is slidably mounted, said strand being secured to the damper to restrain said damper against downward movement, said switch means being movable to a position closing said alarm circuit and said damper descending to cover the air intake opening in said furnace in response to a parting of said strand for actuating said alarm device and stopping the intake of air by the furnace.

5. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit and operable to alternatively close said furnace circuit and said alarm circuit, a heat-fusible strand attached to said switch means and holding said switch means in a position closing said furnace circuit and opening said alarm circuit, a furnace having an air intake opening, a damper mounted on said furnace for movement between positions opening and closing the air intake opening, said strand being secured to the damper to normally restrain said damper in a position opening the air intake opening, said switch means being movable to a position opening said furnace circuit and closing said alarm circuit and said damper being movable to a position closing the air intake opening in said furnace in response to a parting of said strand for shutting off the furnace. actuating said alarm device and stopping the intake of air by the furnace.

6. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said electrical alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit, said switch means comprising a first switch unit movable between open and closed positions in said furnace circuit and a second switch unit being normally open to hold said alarm circuit open, a heat-fusible strand, and means on said strand bearing against said first switch unit and holding said first switch unit in a position closing said furnace circuit, said first switch unit shifting to open position in response to a release of said means bearing thereagainst caused by a parting of said strand and engaging said second switch unit to close said second switch unit for completing the alarm circuit and actuating the alarm device while opening said furnace circuit to shut off the furnace.

7. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said electrical alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit, said switch means comprising a mercury switch having a vial mounted for pivotal movement between open and closed positions, said mercury switch being disposed in said furnace circuit, and a push-button switch having a movable contact and a fixed contact normally maintained in spaced relationship, said push-button switch being disposed in said alarm circuit, a heat-fusible strand attached to said vial of the mercury switch and holding said vial in closed position to complete said furnace circuit, and said vial of the mercury switch being pivotable to open position breaking said furnace circuit and engaging said push-button switch to force said movable contact into abutment with said fixed contact for closing said alarm circuit in response to a parting of said strand for shutting oft the furnace and actuating said alarm device.

8. In a fire alarm system, an electrical alarm circuit, an alarm device disposed in said electrical alarm circuit, an electrical circuit for operation of a furnace, switch means interposed in said alarm circuit and said furnace circuit, said switch means comprising a mercury switch having a vial mounted for pivotal movement between open and closed positions, said mercury switch being disposed in said furnace circuit, and a push-button switch having a movable contact and a fixed contact normally maintained in spaced relationship, said push-button switch being disposed in said alarm circuit, a heat-fusible strand, a collar member afiixed on said strand and bearing against said vial of the mercury switch to hold said vial in closed position to complete said furnace circuit, a furnace operated by said furnace circuit and having an air intake opening, a damper slidably mounted on said furnace above the air intake opening, said strand being secured to the damper to restrain said damper against downward movement, and said vial of the mercury switch being pivotable to open position breaking said furnace circuit and engaging said push-button switch to force said movable contact into abutment with said fixed contact for closing said alarm circuit and said damper descending to cover the air intake opening in said furnace in response to a parting of said strand releasing said collar member from bearing against said vial of the mercury switch for shutting off the furnace, actuating said alarm device and stopping the intake of air by the furnace.

References Cited in the file of this patent UNITED STATES PATENTS 1,176,809 Barton Mar. 28, 1916 1,225,437 Hammond May 8, 1917 1,633,923 Casey June 28, 1927 2,290,047 Hildebrecht July 14, 1942 2,470,711 Moberg May 11, 1949 2,540,527 Ingels Feb. 6, 1951 2,567,112 Kagan Sept. 4, 1951 FOREIGN PATENTS 555,268 Great Britain Aug. 13, 1943

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