GB2112283A - Improvements in or relating to fire-safety systems - Google Patents

Abstract

This invention relates to fire- safety systems for multi-storey buildings, and provides means for clearing smoke from communal units in the building when a fire occurs. The system includes a plurality of fan control units (numbers 1 to 12) each serving to control a pair of fans (P1 to P24). The system also includes a plurality of smoke detectors (SD1 to SD17) connected in groups to detector control units (1 to 11). Each of the fan control units is arranged so that it can deenergise the fans connected thereto, or energise them to run either at low speed or at high speed. The fan control units and the detector control units are interconnected in such a way that, when the mains supply is first connected to the system, all the fans are run up to high speed in succession from the ground floor upwards. Assuming that no smoke is detected by any of the detectors, the fans will then drop back to low speed or stop in accordance with the condition of manual control means in each fan control unit. As soon as smoke is detected, however, by any of the smoke detectors, all the fans will run up to high speed, again commencing from the ground floor upwards. All the fans will reach high-speed operation irrespective of whether they were previously stopped or running at a low speed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fire-safety systems This invention relates to fire-safety systems for multi-storey buildings of the kind which include a plurality of accommodation units and a plurality of communal units providing means of access to said accommodation units.

When a fire occurs in a large multi-storey building such as a block of flats, smoke may penetrate to, and collect in, the communal units making it difficult for the occupants of the building to find their way to the exits from the building.

Accordingly, means may be provided to increase the pressure in the communal units above atmospheric pressure in order to prevent smoke from penetrating to those units from any part of the building where a fire occurs.

From one aspect the invention consists in a fire safety system for a multi-storey building having a plurality of accommodation units and a plurality of communal units providing means of access to said accommodation units, said system including a plurality of smoke detectors associated with said accommodation and communal units; a plurality of electrically driven fans each capable of being energised to run at a relatively low speed and to introduce ventilating air into at least one of said communal units, and each also capable of being energised to run at a relatively high speed and thus to introduce air under increased pressure to said communal unit; and means controlled by said smoke detectors, and responsive to the detection of smoke by any one of said detectors, to energise all said fans to run at said relatively high speed irrespective of whether or not they were energised to run at said relatively low speed prior to the detection of said smoke.

It is to be understood that it is frequently necessary, or at least desirable in a large building, to provide ventilating air to the communal units under normal conditions. Such ventilating air may be provided by means of permanently-open vents, but a more satisfactory solution is to use an electrically driven fan operating at a relatively low speed to provide it. However, under certain conditions, for example in very cold weather, it may be desirable to prevent, or at least reduce, the introduction of the ventilating air into one or more of the communal units. Accordingly, it is desirable that means should be provided for de-energising each fan, or each group of fans. In addition, automatically closing shutters may be provided to restrict entry of air into the building when any particular fan is de-energised.

When a fan is to be used to introduce sufficient air under pressure to restrict the entry of smoke into a communal unit, it must be run at a relatively high speed since the pressure in the communal unit must be maintained at a sufficiently high value to provide a pressure differential across any communications between that communal unit and adjacent accommodation units or other communal units.

It is to be understood that the term "communication" is used herein to include any opening in a boundary wall of the respective communal unit. Normally such "communication" will be constituted solely by the cracks that are present around the doors leading from the communal unit to the accommodation unit or to another communal unit. Air which is thus introduced into the accommodation units under pressure will normally leak from these accommodation units through the cracks that are present around the windows in the exterior walls of the accommodation units. However, if the building is provided with sealed windows, the accommodation units may be provided with unidirectional ventilators which will allow air and smoke to leave the accommodation units, but will not allow air to enter the accommodation units from outside the building.Alternatively, the accommodation units may be provided with ventilators which are normally closed, but which open automatically when smoke is detected anywhere in the building. These automatic opening ventilators may be provided in the exterior walls of the accommodation units or, alternatively, they can be provided at the inner ends of ducts which communicate with the exterior of the building, for example, at roof level.

In some cases, each communal unit will be enclosed by doors which are normally maintained in the closed position. However, in other cases, the doors between the communal units and stairways, halls or lobbeys may normally be held open. In this case, these doors are preferably self-closing doors which are maintained open by means of electromagnetically controlled locking devices which are released when smoke is detected.

It is to be understood that the term "communal unit" as used herein may refer to staircases, halls or lobbeys as well as to corridors. Similarly, the term "accommodation unit" may refer, for example, to offices or flats.

The smoke detectors referred to herein may be of any kind adapted to control electrical apparatus and may be, for example, dependent on the interruption of a light beam or a beam of gammaradiation, or of light-scatter produced by smoke particles. The term "associated" is intended to indicate that one or more smoke detectors may be provided in each communal unit, or in each of the accommoda-ion units communicating with a particular communal unit.

When a communal unit is bounded by one or more exterior walls of the building, it is preferred that the fan, or fans, for that communal unit should be located in the exterior wall, or walls.

However, in the case of a communal unit which is not bounded by any exterior walls, it is necessary to provide a duct from an exterior wall to a wall of the corridor. Preferably this duct should be as short as possible, and the fan should be located at the inner end of the duct so that it operates to reduce the air pressure within the duct.

In some cases, one or more of the communal units will be provided with an air-conditioning system which is additional to any ventilation provided by a system in accordance with the present invention. In this case, the air-conditioning system should be controlled by the smoke detectors so that it is shut-down immediately smoke is detected anywhere in the building, Preferably also automatically closing dampers should be provided at the duct outlets from the air-conditioning system so that the air which is introduced under pressure by the electrically driven fans in accordance with the present invention does not enter the air-conditioning system.

If desired, a fire-safety system in accordance with the present invention may be combined with a fire alarm system so that an audible, and possibly visual, warning is given where ever smoke is detected anywhere in the building and, in addition, the system may be designed to send a signal to a central fire-control office whenever smoke is detected.

In a preferred form of the invention, a control panel is provided for the fan, or fans, on each floor of the building. Each control panel includes means for automatically changing over the fans on the respective floor from low speed to high speed operation when smoke is detected on any floor.

However, the panels are linked together in such a way that, whenever smoke is detected, the fans on the ground floor are run up to high speed first, and thereafter the fans on the higher floors are run up in succession. Each panel also includes means for switching off the fans on its respective floor, but these switch means are over-ridden by the detection of smoke.

Preferably the fans are driven by the alternating current mains supply. Preferably also a standby generator is provided to produce an alternative alternating current supply automatically in the case of mains failure. Preferably the control system, including the smoke detectors, is operated from a low-voltage direct-current supply powered by secondary batteries which are constantly charged by the alternating current mains supply.

Preferably the delay between the running up of the fans on successive floors is adjustable.

Normally two-speed electrically driven fans of the kind which are suitable for use in ventilating and fire-safety systems do not start reliably at low speed. Accordingly, each panel is designed to start all the fans controlled by that panel at high speed and then switch them to low speed for normal running.

As already stated, switch means are preferably provided in each panel to de-energise the fans controlled by that panel. However, these switch means are arranged so that they will only deenergise fans running at low speed, and will not affect the operation of the fans if they are running at high speed as the result of the detection of smoke.

In one embodiment of the invention, the fans are controlled by electro-magnetic relays. In the absence of smoke, these relays are normally energised to keep the fans running at low speed.

However, if smoke is detected by any smoke detector in the building, all these relays are de energised and cause the switching sequence to start so that the fans are run up to high speed successively from the ground floor upwards. In such a system, the alternating current for the fans is normally supplied through an auto-transformer and switching means so that a relatively low voltage can be supplied to the fan under normal conditions to keep it running relatively slowly, while the fu!l mains voltage is applied when smoke is detected to cause the fans to run at high speed.

In an alternative embodiment, the fans are controlled electronically and, in this case, both the switching and the changeover from low speed to high speed may be performed by electronic components.

It is to be understood that smoke detectors, or the control units to which they are connected, normally include latching relays so that, once smoke has been detected, the fans will continue to run at high speed until the activated smoke detector, or the control unit to which it is connected, is reset. This arrangement is normally necessary to prevent hunting. In other words, if no latching relay was provided, the fans would run up to high speed when smoke was detected, but would immediately drop back again to low speed or non-operation as soon as the smoke had been cleared from the activated detector. Assuming that the fire was still burning, smoke would shortly afterwards re-enter the smoke detector, and the sequence would start again. This form of operation is clearly undesirable.However, it is equally undesirable that the fans should continue to operate after the smoke has been completely cleared. Accordingly, in a preferred embodiment of the invention, a timer is provided in association with each group of detectors to reset those detectors, or the control unit associated therewith, after a period of time equal to that required to provide a complete change of air in the space in which that group of detectors is located. Thus, after the air has been completely changed, the fans will drop back to their low speed or non operation. If at this time the fire is no longer burning, no more smoke will be detected, and low speed or non-operation will continue. If, however, smoke is detected by any of the detectors, high speed operation will recommence in the sequence already described.

One embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a simplified block diagram of the electrical system for controlling the fans in one particular fire-safety system in accordance with the invention; and Figure 2 is a simplified circuit diagram of one of the fan control units in the system illustrated in Figure 1.

The particular system illustrated in Figure 1 is intended for a ten-floor building. Each floor of the building, apart from the ground floor, is divided into a plurality of accommodation units, access to which is provided from a communal corridor. A lift shaft interconnects all the floors, and access is provided from the lifts on each floor to the communal corridor on that floor. In addition, all the floors are interconnected by a staircase, and the staircase communicates on each floor with the communal corridor on that floor through a staircase lobby which is normally isolated from the corridor by a self-closing door. The system illustrated includes twenty-four fans controlled by twelve fan control units. Only fan control units numbers 1, 2, 11 and 12 are shown in the drawing.

Fan control unit number 1 controls fans P1 and P2 which are located in a communal unit on the ground floor of the building, and fan control unit number 2 controls fans P3 and P4 which are located in a communal corridor on the first floor.

Fan control unit number 11 controls fan number P2 1 , which is located on the eighth floor of the staircase of the building, and fan number P22 which is located on the sixth floor of the staircase.

Fan control unit number 12 controls fan number P23, which is located on the fourth floor of the staircase, and fan number P24 which is located on the second floor of the staircase. Fan control units numbers 3 to 10 which are not illustrated control fans located on the third to the tenth floors of the building.

Each of the fan control units includes terminals L, N and E which are connected respectively to the line, neutral and Earth terminals of a 240V alternating current supply. The mains supply is connected to a contact breaker C/B1 from which it is distributed to a number of subsidiary contact breakers of which C/B2 and C/B5 are shown in the drawing. As can be seen, contact breaker CiB2 supplies fan control units numbers 1 and 2, and it also supplies fan control unit number 3 which is not illustrated. Contact breaker C/B5 supplies fan control units numbers 11 and 12.

Each of the fan control units also includes output terminals 11,12,13,21,22 and 23. The terminals 11, 12 and 13 of fan control number 1 are connected to fan P 1, and the terminals 21, 22 and 23 of that fan control unit are connected to the fan P2. As will be described in more detail hereinafter, the fans are designed so that they will run at high speed if the line voltage is connected to two of their terminals while the third terminal is connected to neutral, and will run at a lower speed if one of the first-mentioned two terminals is connected to a lower voltage.

The system illustrated also includes smoke detectors SD1 and SD2 located in the communal unit in the ground floor of the building, and smoke detectors SD3 to SD8 located in the communal corridor on the first floor of the building. It also includes smoke detectors SD9 to SD17 which are respectively located in the staircase lobbies on the first, second, third, fourth, fifth, sixth, seventh eighth and ninth floors. Other smoke detectors (not illustrated) are, of course, provided on the remaining floors of the building.

The smoke detectors SD1 and SD2 are connected in series to terminals R1 and R2 of a detector control unit number 1. Similarly, the smoke detectors SD3 to SD8 are connected to the terminals R1 and R2 of a detector control unit number 2. An end-of-line resistors is connected to the left-hand terminals of smoke detector SD1 and, similarly, end-of-line resistors W2 and W1 1 are connected to smoke detectors SD3 and SD9 respectively. A test switch T1 is connected across the terminals R1 and R2 of detector control unit number 1, and test switches T2 and T1 1 are connected respectively to detector control units 2 and 11.The smoke detectors operate so that, if any one of them detects smoke, it provides a short circuit between the terminals R1 and R2 of the detector control unit to which it is connected. A similar short circuit can be provided by manual operation of any of the test switches T1 to T1 1.

The end-of-line resistors W1 to Wi 1 serve to maintain relays in the respective detector control units energised so that, if any of the lines leading to terminals R1 and R2 of the detector control units is broken, the respective relay drops out and operates an alarm system (not illustrated).

The smoke detectors and their control units are run from a 24V battery supply which is shown connected to the terminals V1 and V2 of each detector control unit. Each of the detector control units has a pair of terminals Z1 and Z2, and operates to interconnect these terminals unless smoke is detected. The Z1 terminal of the first detector control unit is connected to the positive battery supply, and the Z2 terminal of this control unit is connected to the Z1 terminal of the second control unit. Similarly, all the Z2 terminals of the remaining control units are connected to the Z1 terminal of the next unit in the series. The Z2 terminal of detector control unit number 11 is connected to a terminal 4 in each of the fan control units.Thus it will be seen that, so long as smoke is not detected by any of the smoke detectors, the 24V supply is maintained on terminal 4 of each of the fan control units.

However, as soon as smoke is detected, the respective detector control unit serves to break the connection between the 24V battery supply and the line connected to all the terminals 4. As will be explained in more detail hereinafter, removal of the 24V supply from terminal 4 causes all the fans to operate at high speed in order to remove smoke from the communal units and thus allow the occupants of the building to escape. To enable the fan control units to respond to the 24V supply of terminal 4 it is, of course, necessary for the negative terminal of the battery also to be connected to each unit, and this connection is provided between terminal V3 of each detector control unit and terminal 3 of each fan control unit.

When a fan is started, it initially draws a much higher current from the mains supply than when it is running normally. Accordingly, as has already been stated, it is necessary to start the fans sequentially and, in the particular system being described, the fans on the ground floor are run up to high speed first, followed by the fans on the higher floors in succession. As will be described hereinafter, the fan control units provide this sequential starting and, for this purpose, they are provided with terminals 1, 2, 5 and 6. The terminals 5 and 6 of fan control unit number 1 are linked together, while terminals 1 and 2 of this unit are connected to terminals 5 and 6 of fan control unit number 2. Similarly, terminals 1 and 2 of each control unit are connected to terminals 5 and 6 of the control unit associated with the next higher floor.Because of the linking of the terminals 5 and 6 of fan control unit number 1, the full 240V supply will be applied to terminals 11 and 12 connected to the fan P 1, and to terminals 21 and 22 connected to the fan P2 as soon as the main supply is connected to the system by means of the circuit breakers. Assuming that, at this time, no smoke is detected by any of the smoke detectors, the full mains voltage will be removed from the terminals 12 and 22 after a predetermined time delay. As a result, the fans P 1 and P2 will run at low speed for normal ventilation purposes. Also after a predetermined time delay, a short circuit will be applied to the terminals 1 and 2 of fan control unit number 1.This will produce a short circuit between the terminals 5 and 6 of fan control unit number 2 with the result that fans P3 and P4 will be started at high speed and, after a run up period, will drop back to low speed for ventilation. This process will be repeated throughout the succession of fan control units until all the fans are running at low speed.

In addition to the equipment already described, each of the fan control units is provided with a manually operabla switch. This switch is arranged to enable the fans controlled by the respective unit to be switched off if normal ventilation is not required. This switching off will not affect the sequence of operations already described except that, in the case of any fan control unit in which the switch is moved to the off position, the fans connected to that control unit after being run up to full speed will run down to zero instead of running down to the low speed operation previously described. If smoke is detected by any of the smoke detectors, all the fans will be run up to high speed in sequence as already described.However, each of the detector control units includes a timer which is set to a period of time equal to that required for the fans to provide a complete change of air in the space in which the smoke detectors connected to that control unit are located. After this period, the timer in the detector control unit connected to the smoke detector which has detected smoke will operate to restore the connection between the terminals Z1 and Z2 which was broken by the detection of smoke.

Thus, assuming that the terminals Z1 and Z2 in all the other detector control units are still interconnected, the 24V supply will be restored to terminal 4 of each of the fan control units, enabling the fans to return to their low speed or stopped condition of operation. If, however, smoke is again detected by any of the smoke detectors, the short circuit between terminals Z1 and Z2 of the detector control unit connected to that smoke detector will once again be broken with the result that the 24V supply will be removed from the terminals 4 of the fan control units so that high speed operation of all the fans is restored.

Figure 2 is a simplied circuit diagram of one of the fan control units illustrated in Figure 1. As already stated, each of these units controls two fans, one of which is connected to the terminals 11, 12 and 13, and the other of which is connected to the terminals 21,22 and 23. The fans are designed so that, if terminals 11 and 12 (21 and 22) are connected to the line side of a 240V alternating current supply, and terminal 13(23) is connected to the neutral line, the fan will run at high speed. On the other hand, if only terminal 11(21) is connected to line while terminal 12 is connected to a low voltage ac supply, the fan will run at a lower speed. However, as already explained, the fans will not necessarily start reliably if terminal 1 2(22) is connected to the low voltage supply while the fan is stationary.

Accordingly, the control unit is designed to connect the terminal 12(22) to line initially even if slow running is required.

As can be seen, auto-transformers T1 and T2 are connected across the 240V ac supply, and terminal 13(23) is permanently connected to neutral. Terminal 11 is connected to line through a relay contact B1, and a relay contact K1, and terminal 12 is connected to line through a relay contact B2. Alternatively, terminal 1 2 may be connected to the low voltage tapping on the autotransformer T1 through a relay contact K2.

Similarly, terminal 21 is connected to line through a relay contact C1 and a relay contact L1, and terminal 22 may be connected to line through a relay contact C2. Terminal 22 may be connected to the low voltage tapping on the autotransformer T2 through a relay contact L2.

The terminals 3 and 4 are connected to a relay A. As already stated, terminal 3 is permanently connected to the negative terminal of the 24V battery supply, and terminal 4 is connected to the positive terminal when no smoke is detected by any of the detectors. Thus the normal condition is that relay A is energised so that its contact Al is changed over from the position illustrated in the drawing. The operation of the fan control unit when the mains supply is first switched on will now be described on the assumption that the relay A is operated.

As can be seen from Figure 1, the fan control unit number 1 has its terminals 5 and 6 interconnected. Thus, when the mains are switched on, the line voltage will be applied through the changed-over contact Al, and the normally closed contact G1 to a relay F. This relay is slow to operate but, after a delay, it will close its contact F1 with the result that relay G will be energised, opening its contact G 1 and closing its contacts G2, G3 and G4. The opening of contact G 1 will release relay F, while the closure of contact G2 will hold relay G. The closure of contact G3 will energise relay H through the normally closed contact J 1. Operation of relay H will close its contact H1 and open its contact H2.

The closure of contact H1 will energise relays B and C through the normally closed contacts M1.

As a result, the contacts B1, B2, C1 and C2 will be closed causing both fans to commence to run at full speed.

The closure of relay contact G3 will also energise relay J through normally closed contacts M2. However, relay J is slow to operate so that it will not de-energise relay H by opening contacts J 1 until the fans have had time to run up to speed.

At the end of its delay period, on the other hand, it will release relay H so that relays B and C are also de-energised with the result that contacts B1, B2, C1 and C2 are all opened. On the other hand, release of relay H will close contacts H2 and, provided the switch contact S1 is closed, relays K and L will be energised. The contacts S1 and S2 are controlled by a manually operated switch which may be used to determine whether the fans will run at low speed for normal ventilation purposes, or will switch off after their initial run up. The contacts S1 and S2 are shown in the positions in which the fans operate at low speed.

Operation of the relays K and L will close the contacts K1, K2, L1 and L2 which will connect the terminals ii and 21 to line and the terminals 12 and 22 to the respective low voltage tappings on the auto-transformers T1 and T2. As a result of this, the fans will run at slow speed for normal ventilation purposes. If, however, the contacts S1 and S2 are manually moved to the opposite position to that shown in the drawings, the relays K and L will not be energized by closure of the contacts H2. On the other hand, the relay M will be energised to open its contacts M1 and M2.

When the contacts M2 open, the relay J will release with the result that its contacts will close to energise relay H. This will close the contacts H1 but, since the contacts M1 are now open, the relays B and C will not be operated thereby.

It is to be understood that operation of the contacts G4 will have interconnected the terminals 1 and 2 which are connected to the terminals 5 and 6 of the next fan control in the series. As a result, in the absence of smoke, the relay F in that unit will energise and commence the sequence of operations as described for the first fan control unit. Again, when relay G operates in the second fan control unit, it will start the sequence in the third fan control unit and so on throughout the series.

If smoke is detected by any of the smoke detectors, the 24V battery supply will be removed from terminal 4 of each of the fan control units. As a result, all the relays A will change over to the position shown in Figure 2. This will release relay G in each of the fan control units and will release relays J, K and L in all the units in which the manually operated switches are in the position to cause the fans to run slowly, and will release the relays H and M in those units in which the manually operated switch is in the position to switch off the fans. In addition, release of the relay A will energise relay D. This relay is slow to operate but, after a time delay, it will close its contact D1 thereby energising the relay E. This will close its contacts El, E3 and E4 and open its contacts E2.Closure of the contacts E3 will hold relay E, and closure of contacts El will energise the relays B and C, thus causing both fans to run up to full speed. Opening of contacts E2 will deenergise relay D. Closure of the contacts E4 will interconnect terminals 1 and 2 thereby interconnecting terminals 5 and 6 of the second fan control unit in the series. Since the contacts Al in this unit will be in the position shown in Figure 2, this will energise the relay D and initiate the sequence just described. Owing to the fact that the relay D is slow to operate, the fans controlled by the second fan control unit will not commence to run until the fans controlled by the first control unit have reached their normal running speed.Once the relay D is operated in the second control unit, it will initiate the sequence of operations in the third unit by operating the relay E and closing the contacts E4. The sequence will continue throughout the series of interconnected fan control units.

After a time delay determined by the timers in the detector control units, the 24V battery supply will be reconnected to terminal 4 in each fan control unit. As a result all the relays A will be changed over so that the relays E will release, thus de-energising relays B and C and disconnecting the power supply from the fans. Release of the relays E will also remove the interconnection between terminals 5 and 6 of each fan control unit except the first.If the 24V supply is maintained on the terminals 4, the relay F in the first fan control unit will operate after a delay, thus starting up the sequence in which the fans controlled by the first fan control unit run up to full speed and then fall back to slow speed or stop, and in which the fans controlled by the second control unit run up to full speed as soon as the fans controlled by the first control unit have reached full speed, this sequence being followed throughout the series. If, on the other hand, smoke is still present in the vicinity of any of the smoke detectors, the 24V supply will be removed from all the terminals 4 as soon as the relevant smoke detector has responded to the presence of smoke. Thus, in this case, the alternative sequence will recommence in which all the fans run up to full speed in succession and remain at full speed until the 24V supply is, once again, restored.

Claims (11)

1. A fire-safety system for a multi-storey building having a plurality of accommodation units and a plurality of communal units providing means of access to said accommodation units, said system including a plurality of smoke detectors associated with said accommodation and communal units; a plurality of electrically driven fans each capable of being energised to run at a relatively low speed and to introduce ventilating air into at least one of said communal units, and each also capable of being energised to run at a relatively high speed and thus to introduce air under increased pressure to said communal unit; and means controlled by said smoke detectors, and responsive to the detection of smoke by any one of said detectors, to energise all said fans to run at said relatively high speed irrespective of whether or not they were energised to run at said relatively low speed prior to the detection of said smoke.

2. A system as claimed in Claim 1 , wherein at least one of the communal units is bounded by one or more exterior walls of the building, and the fan or fans for that communal unit are located in said exterior wall or walls.

3. A system as claimed in Claim 1, wherein at least one of the communal units is not bounded by any exterior walls, and in which a duct is provided from an exterior wall of the building to a wall of said communal unit, a fan being located at the inner end of the duct so that, when it is operating, it serves to reduce the air pressure within the duct and increase the air pressure within the communal unit.

4. A system as claimed in any of the preceding Claims, wherein control units are provided for groups of fans, said control units being linked together in such a way that, whenever smoke is detected, the fans on the ground floor are run up to high speed first, and thereafter the fans on the higher floors are run up in succession.

5. A system as claimed in Claim 4, wherein each control unit includes manually operable means to enable the fans controlled thereby in the absence of smoke to run at low speed or not to run.

6. A system as claimed in Claim 5, in which each control unit is designed to start all the fans controlled thereby at high speed, and then switch them to low speed or non-operation in accordance with the condition of said manually operable means.

7. A system as claimed in Claim 1, in which the fans are controlled by electromagnetic relays which are normally energised in the absence of smoke.

8. A system as claimed in Claim 7, in which, so long as said relays are energised, the fans may be manually controlled to operate at low speed or not to operate.

9. A system as claimed in Claim 8, in which, if smoke is detected by any smoke detector in the building, all said relays are deenergised and cause a switching sequence to start so that the fans are run up to high speed successively from the ground floor upwards.

10. A fire-safety system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying diagrammatic drawings.

11. Any features of novelty, taken singly or in combination, of the fire-safety system hereinbefore described with reference to the accompanying diagrammatic drawings.