TECHNICAL FIELD

This invention relates to fire extinguishers, particularly automatic fire extinguishers.

BACKGROUND ART

Automatic fire extinguishers are known where a reservoir of extinguishing fluid is maintained, where a nozzle is provided through which the extinguishing fluid can be sprayed and where a sensor detects the presence of a fire and opens the nozzle so that the liquid can be sprayed out. Such installations are costly and tend not to be targeted at the precise place where a fire may break out. Particularly when extinguishants such as bromochlorodifluoromethane (BCF) are used, a large volume of extinguishant may have to be dispersed in order to put out a small fire. Since the BCF vapour is environmentally damaging as well as being expensive, there is a requirement to keep the use of the extinguishant to a minimum.

DISCLOSURE OF INVENTION

According to the present invention, there is provided a fire extinguisher comprising an enclosure with thermoplastic walls containing a fire extinguishing medium under pressure.

In use, the extinguisher will be placed with at least part of its thermoplastic wall adjacent to a place where a fire might start. When that place becomes hot, the thermoplastic wall heats up and because of the internal pressure in the enclosure the wall of the enclosure is ruptured and the extinguishing medium sprays out. The

result is an extinguishing of the fire.

In a preferred form, the enclosure is a length of thermoplastic tubing, and the tubing can be wound around a component which' it is necessary to protect from fire. For example the tubing could be wound around and between circuit boards in a computer casing such that if any dangerous overheating occurs on any one of the boards around which the tubing is wound, then the tubing will rupture at that point and put out the fire.

The tubing can be any thermoplastic tubing which is capable of withstanding the necessary internal pressures, and nylon 12 has been found to be a particularly effective material. The internal pressure used will depend upon the nature of the extinguishing medium. When using BCF as the extinguishant, the pressure can be in the range, of 75 to 450 psi (500 to 3,000 kPa) .

BCF is the preferred extinguishant, but other extinguishants such as water and even powder extinguishants can also be used.

The pressurisation of the enclosure can be achieved by the use of a known inert gas, in a manner conventionally known for fire extinguishers.

The internal pressure in the enclosure can be monitored in order to produce alarm signals. When a fire is detected and as a result the enclosure wall is ruptured, then the internal pressure in the enclosure will clearly drop sharply and this pressure can be sensed to operate an audible or visual fire alarm signal. A similar mechanism can also provide a system malfunction signal by responding to a drop in internal pressure which is less than that experienced when the extinguisher discharges, but which is

sufficient to indicate that there is a pressure leak from the extinguisher.

Because the rupturing of the thermoplastic wall and therefore the triggering of the extinguisher is temperature dependant, the extinguisher can operate when a particular temperature is reached, even when this temperature is less than that required to cause a fire to break out. In this way, the extinguisher can work in a preventive capacity and respond to a dangerous situation before a fire actually occurs.

The sensing of a pressure drop in the enclosure can also be used to provide a signal which switches off a power feed to the equipment being protected.

Depending on the application, the enclosure may be entirely in the form of a thermoplastic tube or other enclosure, or the thermoplastic walled part of the enclosure may be directly linked to a reservoir containing a larger quantity of extinguishant.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which :

Figure 1 shows an extinguisher in accordance with the invention in the form of a plastics tube;

Figure 2 shows the extinguisher of Figure 1 after rupturing; and

Figure 3 shows a typical installation in a computer cabinet.

MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows a length of tubing 10 which has its end sealed at 12 and 14. The internal bore of the tube contains an extinguishant 16 which can conveniently be bromochlorodifluoromethane (BCF). Part of the internal bore also contains gas 18 under pressure to pressurise the extinguishant 16.

Figure 1 also shows a fire 20 burning close to the tube. The fire will heat up the tube wall, and as a result partly of the heat and partly of the internal pressure exerted on the tube walls, at a certain critical stage the tube will rupture where it has been softened by the heat and the gas pressure 18 inside the tube will force the extinguishant out onto the fire to extinguish the fire. Such an extinguisher can be very simply made by taking a length of nylon or other thermoplastic tube, sealing one end, filling the interior of the tube about 95% full with BCF under pressure and then supercharging the remaining 5% volume of the tube bore with an inert gas before sealing the other end 12.

The exceptional feature of this extinguisher is that it opens to allow the escape of extinguishant at any point along its length, and at that point which happens to get hot under the particular circumstances. This is to be contrasted with a conventional extinguisher where the nozzle through which the extinguishant escapes is in one fixed position. As a result, the actual quantity of extinguishant needed to put out a fire is very much less resulting in smaller discharges of the environmentally harmful extinguishant.

Figure 3 is a schematic illustration showing an enclosure with walls 20 and a base 22 containing four printed circuit

board cards 24. One side wall and the top wall of the enclosure are omitted in the drawing for the sake of clarity. A flexible nylon tube 26 is placed in the ^' enclosure and is wound in and out between the boards 24. One end 28 of the tube is sealed, and the other end is connected to a gas cylinder 30 outside the enclosure and which contains a reservoir of extinguishant. A pressure meter 32 is also connected to the internal space of the tube 26 to monitor the pressure. An alarm unit 34 is connected to the pressure meter.

This fire extinguisher can be very easily installed into any particular application since the tube 26 is entirely flexible and can be arranged to follow any path through the apparatus. If local overheating occurs at any particular point, then the tube will soften at that point and the internal pressure in the tube will cause the tube to rupture to dispense the extinguishing medium at the point where overheating is occurring. When this happens the pressure in the system will drop and this will be sensed by the meter 32 which will activate an alarm 34 to indicate that a fault condition has occurred. Even if there is no fire damage because the extinguisher has acted before a fire broke out, the location of the fault will be obvious because the rupturing of the tube 26 will be visible. Depending on the application, there may be a requirement for a larger or smaller extinguishant reservoir 30, or indeed it may be dispensed with entirely.

The alarm unit 34 can also operate a switch which closes down all power to the computer in question.

By selecting the wall material and diameter of the tube 10, and the internal pressure of the tube, the extinguisher can be set to operate at any desired temperature. For example when using 6mm diameter nylon 12 tubing with a 4mm or a

4.5mm inside diameter, the operating temperature varied in accordance with the following table.

4.0mm i.d. 4.5mm i.d. Operating temp. 400 psi 285 psi 20°C

345 245 30°C

280 199 40°C

250 180 50°C

225 160 60°C 185 133 70°C

165 115 80°C

155 110 90°C

145 100 100°C

124 85 110°C 105 75 120°C

INDUSTRIAL APPLICABILITY

The invention thus provides an exceptionally simple and effective extinguisher mechanism which can be used in a very wide variety of circumstances, for example under the bonnet of a car.

Because it is only necessary to have an enclosure with thermoplastic wall, an extinguisher of this type could form an integral part of a article moulded from thermoplastic material, if a suitable space which can be charged with extinguishant is provided in the moulding.