GB2264865A - Venting and alarm arrangement - Google Patents

Abstract

A fire detection system includes a vent (2) comprising a duct (4) within which is disposed a temperature-dependent valve arrangement (6, 8, 12). On outbreak of a fire, the temperature of the environment of the vent (2) increases. Between certain temperatures, the valve (6, 8, 12) opens to permit smoke from the fire to be detected by smoke detector (10) in order to trigger a fire alarm. Beyond this temperature range, the valve (6, 8, 12) remains closed for safety. <IMAGE>

Description

VENTING ARRANGEMENT The present invention relates to a venting arrangement for use in a fire detection and alarm system.

Until recently conventional fire detection systems employed, for example, in office blocks comprise a series of point or beam smoke detectors or sensors disposed along the corridors with detection signals being relayed to a remote controller. There are generally no smoke detectors within individual "offices" along the corridor.

In the event of a fire in an office with closed door, a certain amount of time elapses between the fire beginning and sufficient smoke exiting the office to reach the smoke detector and initiate a fire alarm.

This problem can be exacerbated in certain situations where there are tightly fitting fire or smoke doors used between each office and the corridor. The purpose of these types of doors is to hold a fire within an office for as long as possible thereby preventing rapid spread of the fire. Even with conventional doors for the time when the fire is burning in the "office" until the door burns through, relatively little smoke generated will actually exit the room and enter the corridor for detection.Furthermore, of that amount which does enter the corridor, a major proportion of this is "cold" smoke generated by pyrolysis of the door frame because it is generated remote from the fire, the temperature of the smoke drops rapidly on leaving the vicinity of the door, because smoke is more dense than air, this cold smoke falls to the lower regions of the corridor obscuring visibility whilst not activating the ceiling mounted detectors.

It will, therefore, be appreciated that a system whereby ventilation of an "office" is effected on commencement of a fire within the "office", this ventilation then being stopped once sufficient smoke has exited the office in order to activate a smoke detector and hence provide a fire alarm, is desirous and would alleviate the need for separate detectors in each office.

French Patent No. 2511128 discloses a fire shutter with automatically releasing louvres. In the event of a fire, the shutters close ventilation outlets which could help find the fire. Alternatively, the shutters can, in the event of a fire, open to provide a passage for smoke to escape. There is no provision for the shutters to both open and close in the event of a fire.

Such a fire shutter as disclosed in French Patent No.

2511128, whilst providing an improvement over an office having no means of ventilation whatever, suffers from the drawback of being in and remaining in either the open or closed state in the event of a fire.

It would be advantageous to have a ventilation system capable of closing or opening in dependence upon the existance of a fire in a more flexible mode than hitherto available.

It is thus an object of the present invention to at least alleviate the aforementioned problems. Hence, in accordance with a first aspect of the invention, there is provided a venting arrangement for use in a fire detection system comprising; a duct for selectively permitting passage of smoke there through in dependence upon the temperature of the environment of the arrangement; and valve means disposed within the duct, the valve means arranged to be closed when the temperature of the environment is below a first, predetermined threshold level and above a second, predetermined threshold level, and arranged to be open when the temperature of the environment is between the first and second threshold levels.

Thus the present invention is effective to be closed when the temperature of an office, for example, is at its ordinary condition, yet as a fire begins to develop, the vent will open to permit egress of hot smoke developed by the fire into the corridor for detection. As the fire becomes more developed the temperature of the office will continue to rise and so the vent will finally close in order to prevent both more smoke entering the corridor and also unnecessary fuelling of the fire.

Preferably the valve means comprises first and second valve arrangements, the first valve arrangement effective to close at temperatures below the first threshold level and open thereabove, and the second valve arrangement effective to close at temperatures above the second threshold-level and open therebelow. By utilising two valve arrangements, each of which having its own open/close temperature which overlap at least to an extent, a temperature range can be provided within which the vent is open.

Preferably the second valve arrangement comprises intumescent material. Because the swelling of such material occurs as the temperature thereof rises, then the need for a mechanical shutter is obviated at the second threshold level.

This is advantageous because at greatly elevated temperatures, structural damage is possible to mechanical arrangements.

According to a second aspect of the present inventiion there is provided a fire detection system including: a venting arrangement comprising a duct for selectively permitting passage of smoke therethrough in dependence upon the temperature of the environment of the arrangment, and valve means disposed within the duct, the valve means arranged to be closed when the temperature of the environment is below a first, predetermined threshold level and above a second, predetermined threshold level, and arranged to be open when the temperature of the environment is between the first and second threshold levels; and further including a smoke detector for detection of smoke via the duct in order to provide a fire alarm on detection of the smoke.

The invention will now be described, by way of example only, with reference to the following drawings, of which; Figure 1 illlustrates schematically a first embodiment of a venting arrangement, and; Figure 2 illustrates schematically a second embodiment of a venting arrangement.

Referring firstly to Figure 1 it will be seen that a venting arrangement shown generally as 2 comprises a duct 4 within which is disposed a valve means such as a rotatable cylinder 6. The cylinder 6 has formed within it, and throughout a cross-sectional diameter thereof, an open channel 8.

The vent 2 is disposed, for example, in a wall or the like forming a barrier between an office and a corridor adjacent the office. The purpose of the vent 2 is, in the event of a fire in the office, to permit egress of smoke from the office to the corridor in order to be detected and so to initiate a fire alarm. Therefore disposed within the corridor is a smoke detector 10 of conventional form.

The rotation of cylinder 6 is controlled by any suitable means which is temperature-dependent, such as helically wound bi-metallic strip 12. When the temperature of the environment of the vent 2 is below a first, predetermined level such as 1500C, the bimetallic strip 12 is arranged such that the cylinder 6 does not present the open channel 8 to both the office and the corridor. Hence, there is no communication between the office and the corridor via the arrangement, as in figure l(a).

In the event of a fire within the office, the temperature of the office, and hence also the environment of the vent 2, will begin to rise. Once the temperature of the environment of vent 2 reaches the first, predetermined level, in this example 1500C, then the bimetallic strip 12 deforms sufficiently to allow cylinder 6 to rotate to a position where channel 8 communicates with both the office and the corrider as shown in figure l(b).

With vent 2 in this "open" position, smoke generated by the fire within the office is allowed to egress into the corridor where, because sufficient smoke of a relatively high temperature (i.e. compared with the aforementioned "cold" smoke) has been produced, detection at smoke detector 10 occurs.

Whilst vent 2 is in the open position, the fire within the office is not hindered in its development, and indeed may be fuelled by influx of oxygen from the corridor. Thus, as the fire continues to burn and the temperature increases further, the bimetallic strip 12 is arranged to deform further at a second, predetermined level, such as 2000C, to such an extent as to rotate cylinder 6 such that channel 8 no longer communicates with both the office and the corridor once more.

The vent is thus 1'closed", and egress of further smoke from the office to the corridor is prevented, as shown in figure l(c).

For the purpose of clarity, bimetallic strip 12 has been shown only in figure l(d) on the reverse side of cylinder 6 from figures l(a),(b) and (c). It will be apparent that the exact positioning of the bimetallic strip 12 is not crucial so long as the ability to rotate cylinder 6 in dependence upon the first and second temperature threshold is retained.

Referring now to figure 2, in which like components to those in figure 1 are referenced similarly, an alternative embodiment of the present invention will be described.

In the embodiment of figure 2, the valve means has been achieved by provision of two discrete valve arrangements.

The first valve arrangement comprises a flap 14 pivotable about point 16 within the duct 4. The flap 14 is arranged to be closed below the first predetermined temperature and open thereabove. This is achieved by way of biassing means such as a first spring 18 urging flap 14 into a closed position and a second spring 20, being formed from a shape memory alloy such as nickel titanium alloy.

As is known to those skilled in the art, the spring 20 will, on reaching the first predetermined temperature, 1500C tend to retract, to its "memor" length and if the tension of spring 20 is arranged to be greater than that of spring 18, then flap 14 will open.

The second valve arrangement comprises an array of deposits of intumescent material, such as polypropylene containing ammonium polyphosphate 22.

An intumescent material is one which swells in volume at a certain temperature. In the present example, polypropylene containing ammonium polyphosphate 22 allows smoke to flow through the duct 4 at all temperatures below the second predetermined temperature, 2000C (in dependence upon flat 14 being open), yet above 2000C, polypropylene containing ammonium polyphosphate 22 swells to such an extent as to block duct 4 completely thereby preventing passage of any further smoke there through.

A particular advantage afforded by utilising in tumescent material for the second valve arrangement is that, within reasonable limits of fires, whatever the highest temperature within the duct caused by the fire, no disintegration of the valve will occur. This is because the material itself acts as the valve - there are no mechanical components which may melt, or deform to such an extent as to be useless.

It will be appreciated that whilst an array of intumescent deposits has been described, the invention is equally applicable if, for example, more or less intumescent deposits are employed. Also, it will be apparent that the positioning of such deposits may be altered.

It will be apparent to those skilled in the art that whilst the above invention has been described by way of reference to a venting arrangement employed for use in an office/corridor situation, the invention finds broader applications than this specific example.

The present invention described above thus provides for a venting arrangement which, in the event of a fire, allows only a certain amount of smoke away from the area of the fire in order to be detected before preventing passage of further smoke which could be very dangerous either by reducing visibility or by being inhaled.

Claims (10)

1. A venting arrangement for use in a fire detection system comprising; a duct for selectively permitting passage of smoke there through in dependence upon the temperature of the environment of the arrangement; and valve means disposed within the duct, the valve means arranged to be closed when the temperature of the environment is below a first, predetermined threshold level and above a second, predetermined threshold level, and arranged to be open when the temperature of the environment is between the first and second threshold levels.

2. An arrangement according to claim 1 wherein the valve means comprises first and second valve arrangements, the first valve arrangement effective to close at temperatures below the first threshold level and open thereabove, and the second valve arrangement effective to close at temperatures above the second threshold level and open therebelow.

3. An arrangement according to claim 2 wherein the second valve arrangement comprises intwnescent material.

4. An arrangement according to claim 2 wherein the first valve arrangement comprises a plurality of biassing means acting on a flap pivotable within the duct.

5. An arrangement according to claim 4 wherein at least one of said biassing means comprises temperature-dependent shape memory alloy.

6. An arrangement according to either claim 4 or claim 5 wherein the biassing means are springs.

7. An arrangement according to any one of the preceding claims wherein the valve means are arranged for temperature-dependent operation.

8. An arrangement according to any one of the preceding claims wherein the second temperature is higher than the first temperature.

9. An arrangement as substantially herebefore described with reference to the accompanying drawings.

10. A fire detection system including d venting arrangement comprising a duct for selectively permitting passage of smoke there through in dependence upon the temperature of the environment of the arrangment, and valve means disposed within the duct, the valve means arranged to be closed when the temperature of the environment is below a first, predetermined threshold level and above a second, predetermined threshold level, and arranged to be open when the temperature of the environment is between the first and second threshold levels; and further including a smoke detector for detection of smoke via the duct in order to provide a fire alarm on detection of the smoke.