WO2012101443A1

WO2012101443A1 - Fire detector unit

Info

Publication number: WO2012101443A1
Application number: PCT/GB2012/050162
Authority: WO
Inventors: Faruk Meah; Wenwei Zhang
Original assignee: Thorn Security Limited
Priority date: 2011-01-26
Filing date: 2012-01-26
Publication date: 2012-08-02
Also published as: GB2487560A; GB201101360D0; GB2487560B

Abstract

The fire detector unit includes a fire detector and a breakaway detector cover. The breakaway detector cover is attachable to the fire detector, and includes openings therein.

Description

Fire Detector Unit

The present invention relates to detector units of a kind which include a fire detector and a cover mountable so as to protectively cover the fire detector. The fire detector may be any one or more of a range of different types of detectors, such as a smoke detector, a heat detector, a flame detector, a toxic and/or inflammable gas chemical detector, or other hazard detector.

It is important to protect buildings and people from fires by the provision of fire detection and alarm systems including fire detectors within buildings. Certain types of buildings have specific requirements. One of these is prisons. In a prison, some of the inmates are at high risk of suicide, and to reduce this risk, prison cells are designed to minimise the ligature points from which a prisoner might attempt to attach a ligature by which the prisoner might hang him or her self. For this reason, point fire detector units are not used within prison cells because they include a grill which, on the one hand, protects the detector from damage, and permits the detector to sense the environment, for example, permitting passage of any smoke particles to the detector, but on the other hand offers a ligature point to which a ligature can be attached. Prisons are, therefore, typically fitted with aspirator type fire detection systems in which cells include vents through which air is continuously extracted by a pump or fan into a remote fire detector or sampling system. In this way, there is no danger of a prisoner being able to attach a ligature to the detector because it is outside of the cell.

Aspiration type fire detection systems do have drawbacks. For example, the continuous flow of air sucks debris from the area being protected which can block or contaminate the detector. Filters are normally installed in the air flow path ahead of the detector, but these require regular maintenance to clear out the debris drawn into the system. The maintenance costs are high because of the frequent need to clean the filters and regular replacement of contaminated detectors. The build-up of debris can also lead to the cell being less well protected from fires than is intended. It is an aim of the present invention to reduce the disadvantages of aspiration type fire detection systems.

According to a first aspect of the present invention, a fire detector unit comprises a fire detector and a breakaway detector cover attachable to the fire detector and having openings therein.

By the word "breakaway" it is meant that, on the application of a force to the cover away from the fire detector, the detector cover will detach completely from the fire detector without damaging either the detector or the detector cover, and without requiring the cover to be unlatched or otherwise released. Normally, it will be possible simply to reattach the detector cover to the fire detector.

It will be appreciated that known fire detector units which have removable covers also have locking arrangements which require an unlocking action or release action to be taken before the cover is removed. In one known detector unit, a release button must be pressed to release a catch, thereby permitting the cover to be opened on a hinged connection. In another known detector unit, the cover is attached to the detector of the detector unit by placing it on the detector and twisting it clockwise so that locking features of the cover engage with locking features of the detector. Removal of the cover requires the cover to be twisted anti-clockwise to release the locking features before pulling the cover away. In yet another known detector unit, the cover has a circumferential ridge which snap-fits into a bead in the detector so that it can only be removed by squeezing the detector or the cover to distort it so as to release a part of the ridge from the bead to permit removal.

It should be appreciated that all of these known detector units are designed to require a two-stage removal process, firstly to unlock or release the means by which the cover is connected to the detector, and secondly to remove the cover. This has always been considered necessary to avoid unintended dislodging of the cover. In fact, regulations require that a cover must remain in place in the event of certain vibrations, hence the use in known detector units of attachment arrangements which require release or unlocking before removal of the cover. By returning to the use of point fire detectors, much better fire detection performance is achieved while reducing the maintenance costs associated with an aspiration fire detector system. Since air is not being continuously pumped over the detector, it has a much longer service life than an aspiration system where dirt is drawn into the detector. Additionally, the traditional ligature point of the detector cover is eliminated by designing it so that it breaks away from the fire detector long before sufficient force is applied which might cause harm to a prisoner. Thus, the detector cover still has openings to allow ambient air to freely enter the fire detector to detect a fire, but the cover will not bear the weight of a person.

Preferably the fire detector unit further comprises an attachment device arranged to attach the detector cover to the fire detector in such a way that it completely detaches from the fire detector when pulled away from it. Preferably, it is arranged to ensure that the detector cover detaches from the detector on application of a pulling force corresponding to a weight of between 1 and 8 kg, this being much less than the weight of a person, but sufficient to hold the detector cover securely to the fire detector in order to protect the fire detector from damage, more preferably between 2 and 5 kg, and most preferably about 2.5 kg. This range is significant not only because it reduces the chances of a person coming to harm, but also because it is necessary for the detector cover to give sufficient protection to the fire detector. There are various standards which dictate the level of protection that the fire detector must have from its housing, specifying various tests which must be passed including a simulation of a ladder being dropped onto the cover. These ranges are required to meet those standards. The cover must give protection from impacts, mechanical shocks and vibrations.

According to one embodiment, the attachment device includes a magnet carried on at least one of the detector and the cover. In this way, the magnet holds the cover sufficiently securely to the detector, but allows the cover to break away from the detector on application of a force. Being magnetic, the break away occurs without damage to either of the cover or the detector, and the cover can simply be placed back onto the detector. Preferably the embodiment includes a first pair of magnets carried respectively on the detector and on the detector cover so as to attract each other. More preferably, the unit further includes one or more additional pairs of magnets carried on the detector and on the cover, each pair being arranged to attract an opposite one of the pair. The magnets can also be arranged to ensure correct alignment of the cover on the detector.

In the first embodiment, there is an absence of any locking or latching means which requires unlocking or releasing before the cover is separated from the detector. In other words, routine removal of the cover requires a single impulse to be applied to the cover away from the detector to separate it from the detector.

In a second embodiment, the attachment device is a mechanical connection, which, for routine removal of the cover, requires the cover to be unlocked or released before the cover is separated from the detector. Unlocking or release might typically require: the cover to be twisted anti-clockwise to disengage locking elements between the cover and the detector; a button to be pressed to release a latch or interlock; or the cover or detector being gently squeezed to release a part of a locking ridge from a bead in the opposite component. At least a part of the mechanical connection is resilient so as to deform and release the connection when the detector cover is pulled away from the detector without unlocking or releasing the connection. Being resilient, the connection returns to its original shape so as to allow the cover to be refitted.

Preferably, the fire detector unit further comprises a switch arranged to detect whether or not the detector cover is mounted on the fire detector. In the first embodiment, it is appropriate if the switch is constituted by an electrical connection between a pair of magnets disposed respectively on the fire detector and the detector cover, the unit being arranged such that the pairs of magnets touch when the detector cover is mounted on the fire detector. Alternatively, the switch may be constituted by a magnetic field detector which detects the presence or absence of a magnet. The magnetic field detector may include an inductor. An advantage of including the switch is to permit the fire detector unit to draw attention to the removal of a detector cover from a fire detector unit, for example, at a central control panel. According to a second aspect of the present invention, a method of installing a fire detector unit comprises mounting a fire detector on a mounting surface and attaching a breakaway cover to the fire detector.

According to a third aspect of the present invention, a fire detector unit comprises a fire detector; a detachable cover attachable to the fire detector; and a switch arranged to detect whether or not the detector cover is mounted on the fire detector. The switch may include a pair of magnets disposed respectively on the fire detector and the detector cover, the unit being arranged such that the pair of magnets touch when the detector cover is mounted on the fire detector.

Embodiments of the present invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 is an exploded side view of a fire detector unit according to a first embodiment of the present invention;

Figure 2 is a view of the cover of the embodiment shown in Figure 1 from above (inside);

Figure 3 is a view of a cover according to a modified version of the embodiment shown in Figures 1 and 2;

Figure 4 is a view of a cover according to a modified version of the embodiment shown in Figures 1 and 2;

Figure 5 is a view of a cover according to a modified version of the embodiment shown in Figures 1 and 2;

Figure 6 is a view of a cover according to a modified version of the embodiment shown in Figures 1 and 2; and

Figure 7 is a view showing a switching arrangement. Referring first to the embodiment shown in Figures 1 and 2, a fire detector unit 1 is shown including a base 2, a fire detector 3 and a detector cover 4. In use, the base 2 is attached to a ceiling or wall, typically by screws (not shown). The base is normally electrically connected to a fire detection circuit which originates from a central control panel (not shown). The base 2 attaches to the ceiling or a wall so as to fit against the wall without any gaps therebetween, and the connectors within the base 2 are arranged so as to ensure that they do not form any ligature points. The base 2 also includes engagement means, in the form of tabs or sockets or the like by which the fire detector 3 may be attached to the base 2.

Typically, the fire detector 3 engages with the base 2 so that the two become secured together as the detector 3 is twisted clockwise onto the base 2. This kind of connection is well known in the art, and is not described here in detail. Not only does the fire detector 3 engage with the base 2 so as to avoid the fire detector falling, but also to form an electrical connection between the two components. In this way, the fire detector 3 is connected to the electrical fire detection circuit so as to connect it with the central control panel.

The fire detector 3 includes an optical detector chamber 5 which detects smoke particles, a thermistor 6 which detects heat, and a CO cell which detects carbon monoxide. The optical detector chamber 5 includes air entry openings (not shown) by which air enters the optical detector chamber 5 for detection of particles. Of course, the fire detector unit could include any one or more of a number of different types of sensing element, and is not limited to the ones described in this embodiment.

The fire detector 3 also includes a pair of magnets 8.

The fire detector 3 is designed so as to ensure that there are no ligature points.

The detector cover 4 can be installed over the top of the fire detector 3 so as to protect the optical detector chamber 5, the thermistor 6 and the CO cell 7 from physical damage. This is important, and the subject of various product standards involving impact tests and the like. The presence of such rigorous product standards indicates that the detector cover must be very securely attached to the fire detector 3. However, the detector cover 4 must include openings 9 to permit ambient air to freely circulate within the fire detector unit so that any smoke in the ambient air is able to enter the optical detector chamber 5, air is able to reach the CO cell 7 for detection of carbon monoxide, and air is able to reach the thermistor 6 to enable it to correctly detect the temperature in the prison cell. Unfortunately, the openings in the detector cover form potential ligature points.

In order to ensure that the potential ligature point cannot support sufficient weight for harm to be done to a prisoner, the detector cover 4 is designed to break away from the fire detector 3. This is achieved by the positioning of magnets 10 (Figure 2) within the detector cover 4, corresponding to magnets 8, which are able to support the detector cover 4 securely in face to face relationship with the fire detector 3 so as to be able to withstand impacts, such as from ladder strikes, but not so strongly that the cover will not come away from the fire detector 3 upon application of a force at a harmless level.

The force required to separate the cover 4 from the fire detector 3 can be tuned to the specific needs of the environment, but in this case, it would require about 2.5 kg of weight to separate them. The weight might, in other applications, range from 1 to 8 kg, although a more preferred range would be between 2 and 5 kg. This is significantly less than the weight of a person.

In Figure 1 , the magnets 8 in the detector 3 are mounted so that their outward-facing poles are angled outwardly. This is because the magnets 10 on the inside of the cover 4 are mounted on an inclined surface and it is desirable to have the opposing magnets 8,10 arranged so that they are face-to-face, preferably touching. Alternatively, the magnets 10 in the cover 4 could be mounted so as to be angled relative to the inclined inner surface of the cover so that the faces of the poles lie in the plane of the interface between the cover 4 and the detector 3. In that case, the magnets 8 in the detector 3 would be mounted so that their outward-facing poles are not angled outwardly. In this embodiment, the magnets are located towards the edge of the fire detector 3 and detector cover 4. Figure 3 shows a modified arrangement in which the magnets 10 are located closer to the centre of the detector cover 4, and the magnets 8 in the fire detector 3 would be located closer together accordingly. The position of the magnets will depend on where there is space within the fire detector unit, and where the risk of the magnets interfering with the detector unit are minimised. The magnets will also be mounted so that, when the detector cover 4 is securely located on the fire detector 3, an air gap is present between paired magnets in order to avoid wear and tear of the magnets.

It will be evident from Figures 1 to 3 that, were someone to pull the detector cover 4 sufficiently hard that it breaks away from the fire detector 3, no damage will be caused to any of the components, and the detector cover 4 can simply be replaced by offering it back up into position until the magnets 8, 10 engage with each other.

In some embodiments it may be necessary to ensure that the detector cover 4 is always located in the same position when it is mounted on the fire detector 3. This can be achieved through appropriate positioning of the magnets 8, 10. Firstly, they can be spacially positioned so that they will only engage in one position, for example by having them irregularly spaced around the detector. Alternatively, or in addition, pairs of magnets 8, 10 can be arranged with opposite polarities so that, if the detector cover is not correctly aligned, like polarity poles will repel each other to prevent the detector cover from being attached. Examples of some different orientations and arrangements are shown in Figures 4 to 6. In Figure 4, four magnets are positioned "inboard" on the inside of the detector cover 4 with two north poles being positioned next to each other, and two south poles positioned next to each other. The magnets in the fire detector 3 would be arranged in a corresponding pattern. The detector cover 4 could only be located on the fire detector 3 in one position otherwise opposing poles will repel. Of course, where the detector cover 4 must be correctly aligned, it is also possible to include structural elements which prevent misalignment. Such structural elements might include the shape of the fire detector 3 and/or the detector cover, and engagement features such as tabs and indents. Figure 5 shows an arrangement within the detector cover 4 similar to that shown in Figure 4, but with the magnets mounted "outboard". Two magnets with their north poles facing outwards are shown adjacent to each other, with two south poles adjacent to each other on the opposite side of the detector cover 4.

In Figure 6, the magnets are shown mounted outboard, and there are just two of them. To aid alignment, they are arranged with opposite poles.

In the embodiment shown in figures 1 and 2, the fire detector 3 is mounted on a base 2. In other embodiments, these two components may be merged into a single component which is attached to the ceiling.

Any one of a number of magnets can be used. A suitable type is an NdFeB magnet because of its high BH value resulting in a very small sized magnet with high magnetic power, ideal for mounting within a device where space is limited. Other types of magnets can also be used. Cylindrical shaped magnets with polarisation at both ends are best for alignment as well as ease of mounting. In the embodiment, the magnets are arranged in pairs. However, it is also possible to have an arrangement which requires a magnet on one of the fire detector and detector cover, and a material on the other which is attracted by the magnet's field, such as mild steel.

There is one further function that the magnets can contribute to the fire detector unit. This is in the form of a switch. If, instead of positioning the magnets so that there is an air gap between them when the detector cover is mounted on the fire detector, the magnets could be arranged to touch. Since the magnets are metallic, the touching of the magnets could be arranged to constitute an electrical switch being closed. This will require the magnets to be connected in a circuit. When the circuit is opened by the removal of a detector cover, this can be transmitted to the central control panel where a person can be alerted, resulting in action being taken to ensure that the detector cover is replaced. Such an arrangement is shown in Figure 7 in which the two magnets located within the fire detector are respectively connected between an earth and a voltage rail so as to create a potential difference between the two. Opposing magnets within the detector cover are electrically connected to each other through a resistor such that, when the detector cover is mounted on the fire detector, opposing magnets come into contact and close an electrical circuit between the earth and the voltage rail. This generates a voltage which can be fed to a monitoring circuit able to send signals to the central control panel.

Various alternative switching arrangements are also possible which do not require electrical contacts between magnets, but use inductors which can sense the presence or absence of an opposing magnet.

Another alternative is a mechanical switch, such as a microswitch which can indicate to the control panel when the detector cover has been removed.

In the embodiments described above, there is an absence of any locking or latching means which requires unlocking or releasing before the cover is separated from the detector. In other words, routine removal of the cover requires a single impulse or force to be applied to the cover away from the detector to separate it from the detector.

According to a second embodiment of the invention (not shown), the magnets are replaced by resilient clips disposed between the fire detector 3 and the detector cover 4. The clips may be made from metal such as spring steel, or from a resilient plastics material. The clips are designed such that the cover can be secured onto the fire detector 3 with a twist action, and that routine removal of the cover requires the cover to be unlocked or released before the cover is separated from the detector by twisting it anti-clockwise. However, when a force is applied to the detector cover 4 away from the detector unit, the clips will deform to release the detector cover 4. The clips will return to their original shape so that the detector cover 4 can be reattached. In this way, the detector cover can be broken away from the fire detector 3 without causing damage to the clips, the fire detector or the detector cover.

Claims

1. A fire detector unit comprising:

a fire detector; and

a breakaway detector cover attachable to the fire detector and having openings therein.

2. A fire detector unit according to claim 1, further comprising an attachment device arranged to attach the detector cover to the fire detector in such a way that it completely detaches from the fire detector when pulled away from it.

3. A fire detector unit according to claim 2, wherein the attachment device is arranged to ensure that the detector cover detaches from the detector on application of a weight of between 1 and 8 kg.

4. A fire detector unit according to claim 2, wherein the attachment device is arranged to ensure that the detector cover detaches from the detector on application of a weight of between 2 and 5 kg.

5. A fire detector unit according to claim 2, wherein the attachment device is arranged to ensure that the detector cover detaches from the detector on application of a weight of about 2.5 kg.

6. A fire detector unit according to any one of claims 2 to 5, wherein the attachment device includes a magnet carried on at least one of the detector and the cover.

7. A fire detector unit according to claim 6, wherein the attachment device includes a first pair of magnets carried respectively on the detector and on the cover so as to attract each other.

8. A fire detector unit according to claim 7, further comprising one or more additional pairs of magnets carried on the detector and on the cover, each pair being arranged to attract an opposite one of the pair.

9. A fire detector unit according to any one of claims 2 to 5, wherein the attachment device is a mechanical connection, at least a part of the connection being resilient so as to deform and release the connection when the detector cover is pulled away from the detector.

10. A fire detector unit according to any one of claims 1 to 9, further comprising a switch arranged to detect whether or not the detector cover is mounted on the fire detector.

11. A fire detector unit according to claim 10, when dependent on claim 7 or 8, wherein the switch is constituted by an electrical connection between a pair of magnets disposed respectively on the fire detector and the detector cover, the unit being arranged such that the pair of magnets touch when the detector cover is mounted on the fire detector.

12. A fire detector unit according to claim 10, when dependent on any one of claims 6 to 8, wherein the switch is constituted by a magnetic field detector which detects the presence or absence of a magnet.

13. A fire detector unit according to claim 12, wherein the magnetic field detector includes an inductor.

14. A method of installing a fire detector unit, comprising:

mounting a fire detector on a mounting surface; and

attaching a breakaway cover to the fire detector.

15. A fire detector unit comprising:

a fire detector;

a detachable cover attachable to the fire detector; and a switch arranged to detect whether or not the detector cover is mounted on the fire detector.

16. A fire detector unit according to claim 15, wherein the switch includes a pair of magnets disposed respectively on the fire detector and the detector cover, the unit being arranged such that the pair of magnets touch when the detector cover is mounted on the fire detector.