WO1996007166A1

WO1996007166A1 - Device for detecting a fire in a closed-off enclosure

Info

Publication number: WO1996007166A1
Application number: PCT/FR1995/001134
Authority: WO
Inventors: Gérard Scheefer
Original assignee: Scheefer Gerard
Priority date: 1994-09-01
Filing date: 1995-08-30
Publication date: 1996-03-07
Also published as: FR2724247A1; ES2133794T3; DE69509536D1; DE69509536T2; EP0777896B1; AU3261495A; FR2724247B1; EP0777896A1

Abstract

Device (10) for detecting a fire in a closed-off enclosure (12) such as a control panel, comprising means (18) for drawing air from the enclosure, two smoke detectors (20, 22) for continuously analyzing the air drawn from the enclosure and an alarm and control unit (24) connected to the smoke detectors for setting off a warning signal when one of the detectors analyzes and detects smoke in the air from the enclosure and setting off an alarm when the second detector also detects smoke in the air returned to the enclosure.

Description

Fire detection device in a closed enclosure

Technical area :

The present invention relates to fire detection devices and in particular a fire detection device in a closed enclosure such as a control cabinet in a workshop or a production unit in a factory.

State of the art;

In a workshop or production unit, it is conventional for all of the electrical and electronic control circuits to be assembled in a closed and often sealed control cabinet, in order to isolate the circuits from the atmosphere prevailing in the workshop or production unit and keep these circuits away from premature corrosion, dust or malicious acts.

Such a control cabinet is generally provided with a fire detection cabinet located outside the cabinet and responsible for rapidly detecting any start of fire in the cabinet. The box of the type described in FR-A-2,523,455 includes a means of extracting the air from the cabinet, one or two smoke detectors responsible for analyzing the air drawn into the cabinet to detect traces of smoke and through which is forced to circulate the air sucked by the suction means before being discharged to the outside, and a control and alarm unit which generally triggers both an audible alarm and a light alarm when a start of fire is detected.

Unfortunately, the above-mentioned fire detector has two major drawbacks. On the one hand, as it was said previously, the control cabinets are closed and often kept tight and consequently, the suction of the air inside is difficult to do which results in poor operation of the fire detection device. This drawback has been remedied by returning the air which has been sucked into the cabinet in order to bring it to the detection and alarm device, as described in European patent application EP 424 881.

On the other hand, such a detection device must be sensitive to the slightest trace of smoke indicating the start of a small fire. To do this, the alarm must therefore have a high sensitivity for its triggering, this obviously having the disadvantage of the possibility of untimely alarm triggers. To avoid such nuisance tripping, fire detection systems are sometimes provided with two detectors, as is the case in the European patent application cited above; one of the two detectors can also be used to confirm the detection carried out by the other. Unfortunately, such a system which has greater reliability avoiding nuisance tripping in the event that one of the detectors is defective, does not allow detection of a fire on the spot that is both specific (for example on a printed circuit board) and of very little importance.

Presentation of the invention: The object of the invention is therefore to provide a fire detection device in a closed or sealed enclosure, which has a high operating reliability avoiding inadvertent triggering of the alarm while allowing detection of very minor fire outbreaks.

The object of the invention is therefore a fire detection device in a closed enclosure such as a control cabinet, having a means of sucking the air from the enclosure which discharges the air into the enclosure after it has been continuously analyzed by a smoke detection means. In addition, the device includes a control and alarm unit which triggers the fire alarm. when the smoke detection means has detected traces of smoke in the air of the enclosure. The smoke detection means comprises a first detector receiving the air drawn in from the first air inlet ports located at first locations of the enclosure, and a second detector receiving the air drawn in from the second air ports air inlet located at second locations of the enclosure different from the first locations. The control and alarm unit comprises alarm means for triggering the alarm when one of the detectors has detected smoke in the air discharged into the enclosure by the suction and discharge means after that this air gave rise to smoke detection by one of the other detectors.

Brief description of the figures:

The aims, objects and characteristics of the invention will emerge more clearly on reading the following description made with reference to the drawings in which: FIG. 1 schematically represents the preferred embodiment of the fire detection device according to the invention, the FIG. 2 schematically represents an embodiment of the part of the control and alarm unit connected to the two fire detectors, and FIG. 3 schematically represents an enclosure having two fire detection devices corresponding respectively to the two embodiments of the invention.

Detailed description of the invention:

As illustrated in FIG. 1, a box 10 containing the fire detection device according to the invention is placed above an enclosure 12 such as a control cabinet located in a workshop and containing the electrical and electronic circuits workshop control (not shown). The air from the enclosure is sucked in by the two tubes or pipes 14 and 16 by means of a suction means such as a fan 18. The two tubes 14 and 16 can be stopped at any height of the enclosure 12. They are pierced with calibrated orifices a, b, c for the tube 14, or d, e, f for the tube 16, responsible for taking the air in "volumes at risk", that is to say parts of the cabinet containing sensitive circuits or vital parts of all the circuits in the cabinet. The opening of the orifices of the tubes 14 and 16 may be different depending on the level of "risk" of the volume to be monitored.

The air sucked through the tubes 14 and 16 by means of the fan 18 passes through smoke detectors 20 and 22 which may be of the optical, ionic or any other type. Then the air which has just been analyzed by the detectors 20 and 22 is returned to the enclosure 12 by the fan 18. Consequently, the fact that the cabinet 12 is closed or even sealed presents no disadvantage for the device. detection insofar as the air circulates in a closed circuit and does not create vacuum or overpressure detrimental to its proper functioning.

A control and alarm unit 24 is connected to the two smoke detectors 20 and 22. The alarm unit 24 has an audible alarm and / or a light alarm (not shown) which are triggered when the The unit receives information from the two smoke detectors 20 and 22 as explained below.

Assuming that the air taken from the risk volume located near the opening 14-c contains smoke, this air analyzed by the smoke detector 20 causes a pre-alarm signal from the alarm unit 24. However, this pre-alarm must be confirmed because it could be a false alarm by the detector 20. The air which has been analyzed by the detector 20 is blown by the fan 18 in the enclosure. 12. This air is sucked in again, but this time at 16-d, 16-e or 16-f, then analyzed by the smoke detector 22. There are therefore truly an alarm confirmation by the triggering of two detectors placed on two different paths of the intake air. If the air does contain smoke, this is detected and a second signal received by the alarm unit 24 confirms the pre-alarm signal. The alarm (visual and audible) is then triggered by the latter. The information is reliable, confirmed, and can only come from an actual detection of smoke. The reaction time between detection by a smoke detector and its confirmation is very short, less than a few seconds.

It is possible that the enclosure includes so-called special risk zones such as zone 30, in other words high risk zones which it is good to monitor more particularly. In this case, this zone 30 can be connected to one or more holes 14b and 14c by one or more capillary tubes 32 and 34, so that any start of fire in the zone 30 will be very quickly detected by the smoke detector 20 and a pre-alarm signal which will be confirmed once the air containing smoke has been returned to the enclosure by the fan 18, then sucked in by the tube 16. It can therefore be seen that the device of the invention can be easily adapted to each case, without disassembly, but only by connecting capillaries in areas with particular risks.

For the triggering of the alarm, the control and alarm unit 24 can be presented in the manner schematically illustrated in FIG. 3. When the detector 20 detects the presence of smoke in the aspirated air, a contact 36 is closed, which allows a current to flow from the voltage point V into a low value resistor 38. The voltage at the upper terminal of the resistor 38 rises and applies to the input 40 d a comparator 42, the second input 44 of which is supplied by a voltage taken at the junction point of a fixed resistor 46 and a variable resistor 48. The resistor 48 is adjusted so that the voltage on the input 40 is greater than the voltage on the input 44 so that the comparator 42 provides a signal to a pre-alarm means 50 which can be light or sound. When the fire 22 is confirmed by the detector, a contact 52 is closed. Thus, a current is added to the current due to the previous closure of the contact 36 in the resistor 38. The sum of the two currents allows the voltage at the upper terminal of the resistor 38 to rise further, which allows d apply a higher voltage to the first input 54 of the comparator 56 than with the single contact 36 closed. This higher voltage on input 54 then exceeds the voltage applied to the second input 58 of comparator 56 taken at the connection between a fixed resistor 60 and a variable resistor 62. the output of comparator 56 then provides a signal to a means d 'confirmed alarm 64 which can be light or audible.

When the contacts 36 and 52 are open (absence of smoke detection), there is still a line monitoring current flowing in the resistor 38 via the resistor 66. As this current is very low, the voltage at the terminal of the resistor 38 is very low but still provides a voltage on the first input 68 of a comparator 70, higher than the voltage on the second input due to the connection between a fixed resistor 74 and a resistor variable 76. The output of the comparator is supplied to a line monitoring means 78 (for example a dial). The contacts 36 and 52 of the detectors 20 and 22 can be produced by thyristors which, when they become conductive, are equivalent to closed contacts. It should be noted that human intervention is necessary to block the thyristors again, so open the contacts. In other words, both the pre-alarm and the alarm can only be triggered again after being restored to their inactive state. The device which has just been described has the advantage of being usable independently by using a simple 24 volt DC power supply, without adding an expensive detection center. In order to be sure that the device is still in good working order, it must be ensured that the air is correctly sucked from the enclosure. It is indeed foreseeable that the openings a, b, c of the tube 14 or d, e, f of the tube 16 become partially blocked by fouling due for example to an accumulation of dust. This is why a flow detector 26 or 28 is provided at the inlet of each smoke detector. If the suction is poor, the air flow in the tube decreases and drops below a threshold beyond which the operation of the detection device no longer has the required efficiency. Each flow detector 26 or 28 is connected to one control and alarm unit 24 so that an alert signal is also triggered if the flow in one of the tubes falls below the fateful threshold.

The control and alarm unit 24 can be equipped with all the means necessary for the commands: automatic shutdown, ventilation shutdown, anti-sabotage, burglary protection and operating safety of the detectors and the fan.

The detection device which has just been described with reference to FIG. 1 is reversible. Indeed, it suffices to reverse the direction of rotation of the fan so that the air is sucked in from the fan 18 and blown into the enclosure by means of the tubes 14 and 16. In this case, the confirmed alarm arrives more earlier than in the previous case. This configuration is particularly effective if you do not want to sample air precisely in risky volumes or if the cabinet does not have parts to be monitored more particularly. The tubes can therefore be stopped open as soon as they enter the enclosure. We can also plan to use a combination of a detection device according to the first embodiment illustrated in FIG. 1 and of a reverse suction detection device as just mentioned, as shown in FIG. 3. In this case, to the sensitivity of the first detection device 80 comprising long tubes having several openings for volumes at risk, the detection speed of the second detection device 82 comprising short tubes is added, d '' where a very high reliability of the combination of the two devices. In this combination, it can be provided that the output information is connected at will according to an AND or an OR allowing all the most appropriate confirmations, timers and commands in terms of security.

The detection device according to the invention, because of its closed ventilation circuit, can therefore be used for the detection of fire in enclosures that need to be completely sealed so that the circuits located inside are completely isolated. from the outside atmosphere. Thus, such a device is particularly suitable for use in the cabinets of clean rooms or other highly protected environments, in particular in explosion-proof cabinets and environments.

Claims

1. Device (10) for detecting fire in a closed enclosure (12) such as a control cabinet, of the type comprising a means (18) of suction and discharge for sucking the air contained in the enclosure connected to a smoke detection means so that the aspirated air is continuously analyzed, and a control and alarm unit (24) connected to said smoke detection means and intended to trigger an alarm when the analysis of the air from the enclosure by the smoke detector reveals that the air contains smoke, said suction and discharge means (18) forcing air into the enclosure after it has been analyzed by said smoke detection means; said device being characterized in that - said smoke detection means comprises a first detector (20) receiving the air sucked in from first air inlet orifices (14) being at first locations of said enclosure, and a second detector (22) receiving the air sucked in from second air inlet orifices (16) located at second locations of said enclosure different from said first locations, and

- said control and alarm unit comprises means for triggering the alarm when one of said first and second detectors has detected smoke in the air discharged into the enclosure by said suction and discharge means after that this air gave rise to smoke detection by the other of said detectors.

2. Device (10) according to claim 1, in which said alarm means comprise a pre-alarm means (50) triggered by the detection of smoke in the air of the enclosure (12) by one of said first or second detectors (20, 22) and a confirmed alarm means (64) triggered when the other of said detectors detects smoke in the air discharged into the enclosure after said pre-alarm means has been triggered.

3. Device according to claim 1 or 2, further comprising at least one flow detector (26, 28) for measuring the flow of the air analyzed by at least one of said first and second smoke detectors (20, 22) of so as to trigger an alert signal when the suction air flow rate has fallen below a determined threshold, as a result of fouling of the air passage openings.

4. Device according to one of claims 1 to 3, wherein said suction and delivery means (18) is a fan which draws air from the enclosure (12) by means of a first tube (14 ) comprising said first orifices and a second tube (16) comprising said second orifices, said first and second tubes being connected respectively to said fan via said first and second smoke detectors (20, 22), the air being returned directly to the enclosure by the action of said fan.

5. Device according to claim 4, wherein said first (14a, b, c) and second (16d, e, f) orifices for sucking air from the enclosure (12) are placed near the sensitive places so as to quickly detect any fire starting in said sensitive places.

6. Device according to claim 5, in which certain particularly sensitive places (30) of said enclosure (12) are connected to some of said orifices by capillaries (32, 34).

7. Device according to one of claims 1 to 3, wherein said suction and discharge means (18) is a fan which draws air directly from the enclosure (12) and returns it to said enclosure by means of said first tube (14) having said first ports and said second tube (16) having said second ports, after the air has been analyzed in said first and second smoke detectors (20, 22).

8. Fire detection system in a closed enclosure (12) such as a control cabinet comprising in combination a device (30) according to claim 4, 5 or 6 and a device (32) according to claim 7 in operation simultaneous.