US3722597A - Fire protection system with time responsive discharge heads - Google Patents

Abstract

A fire protection system for buildings and the like in which a plurality of extinguishant discharge heads are mounted in an elevated position in the building and are connected to a source of extinguishant. A thermal responsive device is responsive to a fire developing in the building and is adapted to place one or more of the heads in an operable condition for a predetermined time period. The heads that are placed in an operable condition are adapted to be opened in response to a predetermined system condition occuring within the time period.

Description

United States Patent 1 1 1 3,722,597

Friedman 51 Mar. 27, 1973 54 FIRE PROTECTION SYSTEM WITH 3,645,338 2 1972 Livingston ..1s9 42 TIME RESPONSIVE DISCHARGE 3,599,723 8/1971 Vorkapick ..169/42 HEADS 3,587,747 6/1971 Romero et a1 ..l69/42 [75] Inventor: Raymond Friedman, Needham,

Mass. 02062 [73] Assignee: Factory Mutual Research Corporation, Norwood, Mass.

[22] Filed: Aug. 5, 1971 [21] Appl. No.: 169,241

[52] U.S. C1 ..l69/38, 169/42 [51] Int. CI ..A62C 37/08 [58] Field of Search ..169/S, 16, 37, 38, 39, 42

[56] References Cited UNITED STATES PATENTS 2,414,127 1/1947 Shaw ..l69/38 X 2,568,429 9/1951 Burnam et a1. 2,935,135 5/1960 Granttlr. ..169/5 Primary Examiner-Lloyd L. King Attorney-Joseph Lane et a1.

[57] ABSTRACT A fire protection system for buildings and the like in which a plurality of extinguishant discharge heads are mounted in an elevated position in the building and are connected to a source of extinguishant. A thermal responsive device is responsive to a fire developing in the building and is adapted to place one or more of the heads in an operable condition for a predetermined time period. The heads that are placed in an operable condition are adapted to be opened in response to a predetermined system condition occuring within the time period.

16 Claims, 6 Drawing Figures PATENTEUHARZ'HQYS v 3 722.597 SHEET 1 or 2 r INVENTOR RAYMOND, FRIEDMAN ATTORNEYS PATENTlium-mznms 3.722597 SHEET 2 OF 2 FIG. 2.

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INVENTOR RAYMOND FRI EDM AN ATTORNEYS FIRE PROTECTION SYSTEM WITH TIME RESPONSIVE DISCHARGE HEADS BACKGROUND OF THE INVENTION This invention relates to a fire protection system, and more particularly, to such a system employing a plurality of extinguishant discharge heads for discharging extinguishant towards the fire in the space to be protected in response to predetermined conditions.

Recent developments in fire protection systems have attempted to solve the unique fire hazards presented by high-storage enclosures, such as warehouses, etc., which house very large amounts of materials. These materials, which often include highly inflammable plastics and the like, are often stacked to very high levels and develop very high-challenge fires when ignited.

As an example of a type of hazard involved, the fire column, or plume, caused by such fires may exceed twenty feet in height and often flares out beneath the ceiling of the protected space. The increased heat will actuate numerous discharge heads of a fixed fire protection system installed in the building, some of which are located at such a distance from the fire that they are ineffective to deliver the extinguishant to the fuel surfaces. This contributes not only to redundant and flooding use of the extinguishant, but, more significantly, robs the heads directly over the fire from valuable extinguishant needed to extinguish the fire.

In US. patent application Ser. No. 106,652, filed on Dec. 23, 1970, by William L. Livingston and assigned to the same assignee as the present invention, a fixed fire extinguishing system is disclosed which is designed to limit the number of heads which will be activated by fire. This system utilizes heads that are spaced apart relatively long distances and have relatively large outlet orifices to enable greater quantities of water or other extinguishant to be delivered from each head at lower flow rates. Preferably, the heads are in the form of wide angle spray nozzles which develop a downwardly directed spray having large size droplets as compared to the droplets produced by the conventional sprinkler heads. Each nozzle is adapted to be opened by a thermal fuse which is responsive to a predetermined temperature in its immediate vicinity.

With this arrangement, the first nozzle actuated by the fire has a much better possibility of extinguishing the fire, because of the increased ability of the larger droplets to penetrate the fire plume of a high challenge fire. If the heat of the fire spreads, additional nozzles are actuated to help the first nozzle fight the fire and to wet down areas surrounding the fire to provide exposure protection to inhibit the spread of the fire. However, the additional nozzles which are allowed to be actuated are limited to a small number to avoid the problems discussed above. This is achieved by establishing a pressure fioor so that a minimum pressure must exist at each nozzle before it will open, with the system being designed so that this minimum pressure will not be reached until a predetermined number of nozzles have been actuated.

Although this embodiment results in several advantages including increased fire fighting capability and significant cost savings in several respects, it suffers from one disadvantage. Specifically, in establishing the above-mentioned pressure floor, an expellable plug normally blocks the outlet of the nozzle and is adapted to be expelled from the nozzle to permit extinguishant flow therethrough upon the fusing of a conventional temperature responsive device and the presence of a fluid pressure in the nozzle of a magnitude exceeding a predetermined value. In establishing the latter value, a connecter, preferably in the form of a thread, is utilized to retain the expellable plug in a closed position. The design is such that the extinguishant pressure in the nozzle places the thread in tension and must be of a value to break the thread before the expellable plug can be released.

Although providing the several advantages emphasized above, it was subsequently discovered that this pressure floor design could be defeated by delayed increases in the pressure of the system. In particular, assuming that the thermal fuses of a number of nozzles respond to a fire and actuate the nozzles, the pressure floor often operates to prevent a portion of the nozzles from being opened as a result of an inadequate pressure existing at the latter nozzles. However, if at some period of time after this, the system-pressure rises, such as, for example, by the addition of an auxiliary water supply supplied by a fire department or by activating an additional pump, the resulting increase in water supply pressure will then enable some or all of the additional fused nozzles to open. However there may be no fire under these nozzles, with three undesirable consequences: (l) failure to take advantage of the higher pressure to deliver more water to the previously opened nozzles over the fire; (2) increased rate of depletion of the water reservoir, if one is being used; and (3) increased water damage. Even more serious, if the strengthening of the water supply is only of a short duration, and the supply later reverts back to its original condition because of a tactical decision of the fire department, a mechanical failure, a mistake, or any other reason, then the increased number of nozzles remain open at a pressure significantly lower than the the original pressure floor, which may not provide adequate water to suppress the fire. Obviously, this is a deterrent to the fire fighting capability of the system.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fire protection system and discharge head for use in the system, which utilize a pressure floor of the above type, but which eliminate a premature defeating of the pressure floor and the resultant opening of too many discharge heads.

Towards the fulfillment of this and other objects, the fire protection system of the present invention comprises a plurality of extinguishant discharge heads located in a space to be protected, means for connecting said heads to a source of extinguishant, means responsive to a fire developing in said space for placing at least one of said heads in an operable condition for a predetermined time period, and control means for opening said heads placed in said operable condition in response to a predetermined extinguishant pressure.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying drawings for a better understanding of the nature and objects of the present invention. The drawings illustrate the best mode presently contemplated for carrying out the objects of the invention and are not to be construed as restrictions or limitations on its scope. In the drawings:

FIG. 1 is a schematic, perspective view of a building incorporating the fire protection system of the present invention;

FIG. 2 is a vertical cross-sectional view of a nozzle utilized in the system of the present invention;

FIG. 3 is an enlarged partial view similar to FIG. 1, and showing a detail of the nozzle utilized in the system of the present invention; and

FIGS. 4A-4B are partial plan views showing the latching mechanism of the nozzle of FIGS. 2 and 3 in various stages of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a building is shown in phantom lines which is equipped with a fire protection system embodying features of the present invention. The system comprises a feed main 2 connected to a municipal water supply line 4 for delivering an extinguishant, which in this example is water, to a riser 6. The riser 6 is connected to a cross main 8 which, in turn, is connected to a plurality of branch lines 9.

Each branch line has a plurality of nozzle heads which are operated automatically in response to a fire, as will be described, to deliver a downwardly directed spray of water droplets on the fire. The feed main 2 extends beyond the riser 6 and can be connected to risers of other buildings or, in the case of a large building, to other risers in the same building. The cross main 8 and the branch lines 9 are suspended near the ceiling of the building in a conventional manner, and the connections between the various pipes of the system are also made in a conventional manner.

A nozzle 10 is shown in detail in FIGS. 2 4 and comprises a cylindrical body 12- having an upper end portion which is internally threaded as shown at 14 for connection to a source of extinguishant, and a lower end portion which defines an outlet orifice 16 of a reduced cross-section. A pair of spiral vanes 18a and 1812 are fixed within the body 12 for imparting a swirling motion to water flowing downwardly therethrough in a conventional manner. The vanes 18d and 18!: support a hollow central hub 20 which, in turn, slidably supports a rod 22 having a piston head 24 fixed on its lower end.

A pair of sealing rings 26 and 28 are positioned about the periphery of the head 22 and sealingly engage the inner wall of the body 12 near the outlet orifice 16. A fusible nut 30 is located in the outlet orifice 26 adjacent the plug 24, to provide a safeguard against premature expulsion of the rod 22, and to prevent an accumulation of dirt and grime in the outlet orifice which might otherwise affect the expulsion of the plug in the event of fire.

The rod 22 is latched in the position shown in FIG. 2 by a rod 32 which extends slidably through an externally threaded boss 34 projecting from the side of the body 12. The assembly for achieving the latching will be described in detail later.

A sleeve 38 is threaded on the end of the boss 34. The outer end of the sleeve is closed off by an externally threaded stub shaft 40 having a ring or yoke 42 thereon. The rod 32 slidably extends through the stub shaft 40, and the other end of the rod engages a conventional thermal fuse element 44 positioned within the ring 42. The fuse element prevents movement of the rod 32 to the right as viewed in FIG. 2, until the heat of a fire fuses the element 44 so that it collapses. Since the element 44 is the standard type commonly used in conventional sprinkler heads now on the market, it will not be described in greater detail.

The rod 32 has a piston head 46 mounted thereon which slidably engages the internal wall of the sleeve 38. A spring 48 is positioned between the boss 34 and the piston head 46 to bias the piston head and the rod 32 to the right with a predetermined biasing force. A plate 50 is disposed in the sleeve 38 and divides the space between the piston head 46 and the stub shaft 40 into two chambers 52 and 54, with the chamber 52 containing a viscous fluid and the chamber 54 contain-' ing only atmospheric air that is trapped therein. An opening 56 extends through the plate 50 for receiving the rod 32 with a slight clearance to permit passage of the fluid from the chamber 52 into the chamber 54 upon movement of the piston head 46 to the right.

With this arrangement, the piston head 46 and the rod 32 will be driven to the right under the action of the spring 48 upon the fuse element 44 collapsing in response to the heat of the fire. This movement will be dampened by the fluid passing from the chamber 52, through the restricted opening 56, and into the chamber 54, with the size of the latter chamber being selected so that the force resulting from the compression of the air therein is readily overcome by the force of the spring 48.

As better shown in FIG. 3 a thread 58 is provided which has one end fastened to the upper end of the rod 22. The thread 58 extends through an opening 59 formed through an end portion of the hub 20 extending above the vane 18a, and the otherend of the thread is fastened to the latter end. The above-mentioned fastening maybe achieved in any conventional manner, such as by the use of epoxy or the like. The thread is preferably of a nylon material and its length is selected so that it will have a slight slack therein in the deactivated position of FIG. 2 to avoid any unwanted tension being placed thereon due toslight dimensional variations of the other components of the nozzle.

The assembly for latching the rod 22 in the position shown in FIG. 2 is better shown with reference to FIGS. 3 and 4. In particular, the rod 32 extends through two slots formed in diametrically opposite walls of the portion of the hub 20 extending above the upper plane of the vane member 18a. The portion of the rod 32 extending within the hub 20 is enlarged as shown at 60 and has a generally elliptical slot 62 formed therein. A pair of inwardly directed tabs 64a and 64b are formed on the enlarged portion 60 of the rod 32 and are disposed at opposite ends of the slot 62. The rod 22 has an enlarged head 66 of a circular shape which is of a diameter slightly less than the distance between the ends of the tabs 64a and 64b.

In the normal latched position of FIGS. 2, 3, and 4A, the head 66 is retained in the position shown by means of the tab 64b extending underneath the head 66, thereby preventing a release of the latter and therefore the rod 22.

However, upon movement of the rod 32 to the right as viewed in the drawings, the enlarged portion 60 of the rod 32 will move relative to the head 66 and permit the latter to clear the tabs 64b and 64a and thus release the rod 22. On further movement of the rod 32, and therefore the enlarged portion 60, to the right, the assembly will attain the position shown in FIG. 4C, with the tab 64 a extending underneath the head 66 of the rod 22. In this position, as in the position of FIG. 4A, the head 66, and therefore the rod 22, is latched in the position shown in FIG. 2.

In operation, the nozzle is installed at an elevated position in the structure to be protected in the condition shown in FIGS. 2, 3, and 4A, i.e., with the rod 22 latched in the body member by virtue of the tab 64b extending underneath the head 66, and with the thread 58 fixed to-the rod 22 and the upper end of the hub 20. If both the fusible link 44 and the fusible link nut 30 are thermally actuated in response to an elevated temperature in their vicinity, the tension of the spring 48 will cause the piston head 46 to move to the right as viewed in FIG. 2, with this movement being dampened by virtue of the fluid moving from the chamber 52, through the restricted orifice 56, and into the chamber 54. An initial portion of this movement enables the enlarged portion 60 of the rod 32 to attain the positive relative to the head 66 of the rod 22 shown in FIG. 4B, and thus free the rod 22 for discharge from the body member 12. At this point, the pressure of the extinguishant in the body member 12 acts on the inner face of the plug 24 and forces it downwardly to cause a tension to be applied to the thread 58 in direct proportion to the amount of the pressure. If this pressure is sufficient to break the thread, the rod 22 will be completely released and therefore it, along with the plug member 24, will be discharged outwardly from the body member 12 by the force of the extinguishant pressure. Of course, if the extinguishant pressure is not sufficient to break the thread 58, the plug 24 will not be expelled from the body portion 12 despite release of the fuse element 44 and the fusible nut 30.

After a predetermined time delay the rod 32, in continuing its movement to the right, will cause the enlarged portion 60 to attain the position shown in FIG. 4C, with the tab 64a extending underneath the head 66 of the rod 22. At this point the rod 22, and therefore the plug 24, will be latched relative to the body member 12 no matter what value the pressure of the extinguishant in the body member attains.

It can be appreciated from the foregoing that the above arrangement permits the plug 24 to be discharged from the body member 12 in response to a predetermined extinguishant pressure existing in the body member 12 only for a predetermined time period after the actuation of the thermal link 44 and the fusible nut 30. As emphasized above, this eliminates the possibility of the opening of a nozzle or nozzles by virtue of a temporary delayed increase in the extinguishant pressure available to the system. The above arrangement eliminates unnecessary water damage, and prevents the critical nozzles nearest the fire from being robbed of extinguishant as a result of an excessive number of nozzles being actuated at points remote from the fire in response to a temporary increase in the system pressure.

Of course, other variations of the specific construction and arrangement of the time responsive pressure floor for fire protection systems disclosed above can be made by those skilled in the art without departing from the invention as defined in the appendedclaims.

I claim:

l. A fire protection system for buildings and the like comprising a plurality of extinguishant discharge heads located in a space to be protected, means for connecting said heads to a source of extinguishant, a fusible member for each of said heads for normally retaining said head closed, said fusible member being responsive to a predetermined temperature in said space for conditioning said head for opening, and control means for each of said heads for opening said head in response to the extinguishant pressure at said head exceeding a predetermined minimum value during a predetermined time period after said head has been conditioned by said fusible member, said control means maintaining closed those heads whichare not opened during said time period irrespective of the extinguishant pressure at said latter heads.

2. The system of claim 1 wherein end of said head includes a closure member normally preventing the flow of extinguishant through the head, said head opening on the discharge of said closure member from said head, and wherein said control means further comprises a spring loaded rod connecting said fusible member and said closure member and adapted-to move relative to said closure member upon the fusing of said fusible member.

3. The system of claim 2 wherein said rod includes latching means adapted to latch said closure member to said head prior to the fusing of said fusible means and adapted to release said closure member upon a predetermined movement of said rod.

4. The system of claim 3 wherein said latching means is further adapted to latch said closure member to said head after an additional predetermined movement of said rod in the absence of said predetermined minimum pressure at said head, the total movement of said rod corresponding to said time delay.

5. The system of claim 4 wherein said control means further comprises means to dampen said movement.

6. In combination, an extinguishant dispersing head for an automatic sprinkler system for protecting a building, fire responsive means for conditioning said head for opening in response to information received from a fire in said space, and control means for opening said head in response to the extinguishant pressure at said head exceeding a predetermined value within a predetermined time period after the head has been conditioned by said fire responsive means, said control means maintaining said head closed irrespective of information received from said system if it is not opened during said time delay.

7 The system of claim 6 wherein said fire responsive means comprises a fusible member for said head normally retaining said head closed and responsive to a predetermined temperature for activating said control means and initiating said time delay.

8. The system of claim 7 wherein said control means comprises means for said head which, when activated by said fusible member, maintains said head closed it the pressure at said head is below said predetermined minimum pressure and opens said head if the pressure at said head exceeds said predetermined minimum pressure during said time delay, and means to maintain said head closed after said time delay irrespective of the pressure at said head if' it has not opened during said time delay.

9. The system of claim 7 wherein each of said heads includes a closure member normally preventing the flow of extinguishant through the head, said head opening on the discharge of said closure member from said head, and wherein said control means comprises a spring loaded rod connecting said fusible member and said closure member and adapted to move relative to said closure member upon the fusing of said fusible member.

10. The system of claim 9 wherein said rod includes latching means adapted to latch said closure member to said head prior to the fusing of said fusible means and adapted to release said closure member upon a predetermined movement of said rod.

11. The system of claim 10 wherein said latching means is further adapted to latch said closure member to said head after an additional predetermined movement of said rod in the absence of said predetermined minimum pressure at said head, the total movement of said rod corresponding to said time delay.

12. The system of claim 11 wherein said control means further comprises means to dampen said movement.

13. In combination, an extinguishant dispersing head for an automatic sprinkler system for protecting a building, fire responsive means for conditioning said head for opening in response to information received from a fire in said space, and control means for controlling the opening of said conditioned head in response to information received from the system within a predetermined time delay after the head has been conditioned by said fire responsive means, said control means maintaining said head closed irrespective of information received from said system if it is not opened during said time delay, said head having an inlet adapted to be connected to a source of the extinguishant, an outlet for spraying the extinguishant on a fire and a closure member positioned between said inlet and outlet for preventing extinguishant flow through said outlet, said control means comprising latch means having a first deactivated condition, an activated condition and a second deactivated condition, said control means locking said closure member in its closed position in said head in said first deactivated condition, said control means automatically placing itself in said second deactivated condition within a predetermined time period after the initiation of said activated condition, said control means in said activated condition controlling said closure member for opening automatically if the extinguishant pressure in said head exceeds a predetermined minimum pressure, said control means in said second deactivated condition locking said closure member in its closed position irrespective of the extinguishant pressure in said head if the closure member has not been opened during said activated condition, said fire responsive means normally maintaining said control means in said deactivated condition and placing said control means in said activated condition in response to information received from a fire in said space.

14. A fire protec ion system for buildings and the like comprising a plurality of extinguishant discharge heads located in a space to be protected, means for connecting said heads to a source of extinguishant, fire responsive means responsive to a fire developing in said space for conditioning said heads for opening in a sequence dictated by information received from the tire, and pressure responsive means for opening said conditioned heads in response to the existence of a predetermined extinguishant pressure in said system within a predetermined time period after each head has been conditioned by said fire responsive means, said pressure responsive means maintaining closed those heads which are not opened during said time period irrespective of the extinguishant pressure in said system.

15. The system as defined in claim 14 wherein said pressure responsive means is responsive to the extinguishant pressure at each of said heads during said time delay, said pressure responsive means opening each head if the pressure is greater than a predetermined minimum pressure during said time delay.

16. The system of claim 15 wherein said fire responsive means comprises a fusible member for each of said heads normally retaining said head closed and responsive to a predetermined temperature for activating said pressure responsive means and initiating said time delay.

Claims (16)

1. A fire protection system for buildings and the like comprising a plurality of extinguishant discharge heads located in a space to be protected, means for connecting said heads to a source of extinguishant, a fusible member for each of said heads for normally retaining said head closed, said fusible member being responsive to a predetermined temperature in said space for conditioning said head for opening, and control means for each of said heads for opening said head in response to the extinguishant pressure at said head exceeding a predetermined minimum value during a predetermined time period after said head has been conditioned by said fusible member, said control means maintaining closed those heads which are not opened during said time period irrespective of the extinguishant pressure at said latter heads.

2. The system of claim 1 wherein end of said head includes a closure member normally preventing the flow of extinguishant through the head, said head opening on the discharge of said closure member from said head, and wherein said control means further comprises a spring loaded rod connecting said fusible member and said closure member and adapted to move relative to said closure member upon the fusing of said fusible member.

3. The system of claim 2 wherein said rod includes latching means adapted to latch said closure member to said head prior to the fusing of said fusible means and adapted to release said closure member upon a predetermined movement of said rod.

4. The system of claim 3 wherein said latching means is further adapted to latch said closure member to said head after an additional predetermined movement of said rod in the absence of said predetermined minimum pressure at said head, the total movement of said rod corresponding to said time delay.

5. The system of claim 4 wherein said control means Further comprises means to dampen said movement.

6. In combination, an extinguishant dispersing head for an automatic sprinkler system for protecting a building, fire responsive means for conditioning said head for opening in response to information received from a fire in said space, and control means for opening said head in response to the extinguishant pressure at said head exceeding a predetermined value within a predetermined time period after the head has been conditioned by said fire responsive means, said control means maintaining said head closed irrespective of information received from said system if it is not opened during said time delay.

7. The system of claim 6 wherein said fire responsive means comprises a fusible member for said head normally retaining said head closed and responsive to a predetermined temperature for activating said control means and initiating said time delay.

8. The system of claim 7 wherein said control means comprises means for said head which, when activated by said fusible member, maintains said head closed if the pressure at said head is below said predetermined minimum pressure and opens said head if the pressure at said head exceeds said predetermined minimum pressure during said time delay, and means to maintain said head closed after said time delay irrespective of the pressure at said head if it has not opened during said time delay.

9. The system of claim 7 wherein each of said heads includes a closure member normally preventing the flow of extinguishant through the head, said head opening on the discharge of said closure member from said head, and wherein said control means comprises a spring loaded rod connecting said fusible member and said closure member and adapted to move relative to said closure member upon the fusing of said fusible member.

10. The system of claim 9 wherein said rod includes latching means adapted to latch said closure member to said head prior to the fusing of said fusible means and adapted to release said closure member upon a predetermined movement of said rod.

11. The system of claim 10 wherein said latching means is further adapted to latch said closure member to said head after an additional predetermined movement of said rod in the absence of said predetermined minimum pressure at said head, the total movement of said rod corresponding to said time delay.

12. The system of claim 11 wherein said control means further comprises means to dampen said movement.

13. In combination, an extinguishant dispersing head for an automatic sprinkler system for protecting a building, fire responsive means for conditioning said head for opening in response to information received from a fire in said space, and control means for controlling the opening of said conditioned head in response to information received from the system within a predetermined time delay after the head has been conditioned by said fire responsive means, said control means maintaining said head closed irrespective of information received from said system if it is not opened during said time delay, said head having an inlet adapted to be connected to a source of the extinguishant, an outlet for spraying the extinguishant on a fire and a closure member positioned between said inlet and outlet for preventing extinguishant flow through said outlet, said control means comprising latch means having a first deactivated condition, an activated condition and a second deactivated condition, said control means locking said closure member in its closed position in said head in said first deactivated condition, said control means automatically placing itself in said second deactivated condition within a predetermined time period after the initiation of said activated condition, said control means in said activated condition controlling said closure member for opening automatically if the extinguishant pressure in said head exceeds a predetermined minimum pressure, said control means in said second deactivated condition locking said closUre member in its closed position irrespective of the extinguishant pressure in said head if the closure member has not been opened during said activated condition, said fire responsive means normally maintaining said control means in said deactivated condition and placing said control means in said activated condition in response to information received from a fire in said space.

14. A fire protection system for buildings and the like comprising a plurality of extinguishant discharge heads located in a space to be protected, means for connecting said heads to a source of extinguishant, fire responsive means responsive to a fire developing in said space for conditioning said heads for opening in a sequence dictated by information received from the fire, and pressure responsive means for opening said conditioned heads in response to the existence of a predetermined extinguishant pressure in said system within a predetermined time period after each head has been conditioned by said fire responsive means, said pressure responsive means maintaining closed those heads which are not opened during said time period irrespective of the extinguishant pressure in said system.

15. The system as defined in claim 14 wherein said pressure responsive means is responsive to the extinguishant pressure at each of said heads during said time delay, said pressure responsive means opening each head if the pressure is greater than a predetermined minimum pressure during said time delay.

16. The system of claim 15 wherein said fire responsive means comprises a fusible member for each of said heads normally retaining said head closed and responsive to a predetermined temperature for activating said pressure responsive means and initiating said time delay.

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