Fire detection

Abstract

A particle detection system including a particle detector in fluid communication with at least two sample inlets for receiving a sample flow from a monitored region. The particle detector includes detection means for detecting the level of particles within the sample flow and outputting a first signal indicative of the level of particles within the sample flow. A flow sensor is located downstream of the sample inlets for measuring the flow rate of the sample flow and outputting a second signal indicative of the flow rate of the sample flow. At least a first sample inlet is normally open to the monitored region for receiving at least part of the sample flow. At least a second sample inlet is normally closed to the monitored region but is openable to the monitored region in response to a change in environmental conditions in the monitored region. The particle detection system further includes processing means adapted for receiving the first and second signals and comparing the first signal to a predetermined threshold level and comparing the second signal to a predetermined threshold flow rate, and generating an output signal based on the respective comparisons of the first and second signals. A method of particle detection is also described.

Claims

1. A method of particle detection including: analysing an air sample from an air volume being monitored and determining a level of first particles in the air sample; analysing a flow rate of the air sample from the air volume and determining a flow rate of the air sample; processing the level of particles in the air sample in accordance with at least one first alarm criterion and processing the flow rate of the air sample in accordance with at least one second alarm criterion, wherein the second alarm criterion is a threshold flow rate and is indicative of a possible heat event; and performing an action.

2. The method of particle detection according to claim 1, wherein the step of performing an action includes sending a signal, a signal indicative of an alarm or fault condition, a change in an alarm or fault condition, a pre-alarm or pre-fault condition or other signal, a signal indicative of either or both of the level of particles and flow rate.

3. The method of particle detection according to claim 1, wherein the first alarm criterion is a threshold particle level and is indicative of a possible smoke event.

4. The method of particle detection according to claim 1, wherein the air sample and the flow rate can be analysed simultaneously, consecutively or alternately.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described, by way of example only, with reference to the accompanying drawings in which;

(2) FIG. 1 is a schematic representation of a conventional aspirated particle detection system;

(3) FIG. 2 is a schematic representation of an alternate form of conventional aspirated particle detection system; and

(4) FIG. 3 is a schematic representation of an aspirated particle detection system according to an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

(5) An aspirated particle detection system 10 is shown in FIG. 1, and comprises a pipe 12 having a number of sampling inlets shown as points 14, and a detector 16.

(6) The detector may be any type of particle detector, comprising for example a particle counting type system such as a VESDA LaserPlus smoke detector sold by the applicant. Typically the detector 16 comprises a detection chamber, indicator means and an aspirator for drawing sampled air through the pipe into the detection chamber.

(7) In operation, each sampling point 14 may be placed in a location where smoke detection is required. In this way a sampling point 14 acts to detect smoke in a region.

(8) A second embodiment of a particle detection system is shown in FIG. 2, where a pipe network 20 comprising a number of pipes 22 with sampling points 24 is shown. A similar detector to the detector 16 shown in FIG. 1 may be used. One pipe 22 may consist of a branch, such as branch A in FIG. 2.

(9) In the above systems, air is drawn through sample points 14, 24 and into the pipe 12, 22. The pipe 12 (or 24), will have a number of sampling points 14, (or 24), and therefore air will be drawn through all sampling points within a single pipe when the sampling points are open.

(10) Typically there are 2 commonly used styles of sampling points in aspirated particle detectors. The first type of sample point is a simple hole drilled in a sampling pipe 12. Typically the hole may be of 3 mm diameter, while a pipe may be of 25 mm outer diameter; though these figures will vary from design-to-design and from region to-region. The second style of sampling point is typically in the form of a nozzle connected to the sample pipe 12 by a length of relatively narrow flexible hose.

(11) Referring to the embodiment of the invention illustrated in FIG. 3, a flow sensor 30 is provided downstream of the sampling points 34, either before or after the detector 16. Sampling points 34 are the same as sampling points 14, 24 described above and under normal ambient conditions are open to the monitored region.

(12) In the embodiment illustrated a flow sensor 30 is provided in each pipe 32 immediately upstream of the detector 16. The flow sensor 30 may take a number of forms. In one embodiment an ultrasonic flow meter is used. The ultrasonic flow meter comprises two transducers spaced apart by a known distance, exposed to but not necessarily in the air flow into the sampling point. The flow is detected by measuring time of flight of an ultrasound waveform or signal transmitted from one transducer to another. The use of ultrasonic transducers allows for accurate measurement of airflow, while providing low resistance to air flow, as the transducers do not need to project into the airstream. Each flow sensor outputs a reading, for example in liters of air per minute, to a processor (not shown). Thermal flow sensors such as the resistance temperature detectors employed in the VESDA LaserPlus smoke detector may also be used in the present invention.

(13) Heat activated sampling points 36 are provided in one or more of the pipes 32. In this embodiment, one heat activated sampling point is provided in each pipe 32 but there may of course be more than one heat activated sampling point in each pipe 32. Sampling points 36 are shown located towards an end of pipe 32 but they may be positioned anywhere along the pipe 32 depending on the region to be monitored. The heat activated sampling points 36 may have the same cross-sectional area in communication with the monitored region as sampling points 34 although it is preferred that sampling points 36 either have a larger cross-sectional area or that there is a higher ratio of heat activated sampling points 36 to sampling points 34. This allows a larger increase in flow rate to be introduced to the sampling pipe 32 in the event the sampling points 36 are activated.

(14) In preferred embodiments of the invention heat activated sampling points 36 are used in the sampling pipe network in conjunction with conventional sampling points 34 described above. The heat activated sampling points 36 comprise a housing (not illustrated) that allows the flow of air from a monitored region into a sampling pipe and to detector 16. The housing is blocked by a plug that is either formed from or retained by a substance with a predetermined melting point such as a sealant or wax. When the temperature in the monitored region reaches the predetermined melting point of the wax, the plug either melts or falls away thereby opening the housing and allowing air into the sampling pipe from the monitored region. The increase in flow is measured by the flow sensor which effectively detects a flow fault and sends a signal to the processor.

(15) In a preferred embodiment of the invention the detector 16 includes detection means for detecting the level of particles within the sample flow and outputting a first signal indicative of the level of particles within the sample flow to a processor (not shown). Similarly the flow sensor 30 measures the flow rate of the sample flow and outputs a second signal indicative of the flow rate of the sample flow to the processor.

(16) The processor receives the first and second signals and compares the first signal to a predetermined threshold level and compares the second signal to a predetermined threshold flow rate. As a result of the respective comparison the processor generates an output signal.

(17) There are four output signals or alarm states that may be generated by the processor:

(18) TABLE-US-00001 No smoke Smoke No Particles detected in air sample Particles detected in air sample heat below threshold level above threshold level Flow rate of air sample below Flow rate of air sample below threshold level threshold level Heat Particles detected in air sample Particles detected in air sample below threshold level above threshold level Flow rate of air sample above Flow rate of air sample above threshold level threshold level

(19) At the first alarm level particles detected in air sample are below a threshold level and the flow rate of air sample is below a threshold level. This indicates that there is no smoke or heat, i.e. no fire, and no alarm is raised.

(20) At the second alarm level, particles detected in the air sample are below a threshold level and the flow rate of the air sample is above a threshold level. This indicates that there is heat or a flow fault, such as a sampling pipe breakage, in the monitored region but no smoke. A signal is generated to further investigate the monitored region and to rectify the flow fault. This may include a visual inspection for example.

(21) At the third alarm level particles detected in the air sample are above a threshold level and the flow rate of the air sample is below a threshold level. This indicates that there may be smoke present but no heat. In this instance a signal is generated to further investigate the monitored region. The detector may include a secondary particle detection stage that can be used to further verify the type and/or level of particles in the sample flow.

(22) At the fourth alarm level particles detected in the air sample are above a threshold level and the flow rate of the air sample is above a threshold level. This indicates that there is smoke and either heat or a flow fault present in the monitored region. An alarm is activated to urgently investigate the monitored region, fire authorities may be notified, and fire suppression devices may be activated.

(23) In certain embodiments a lower threshold flow rate may also be monitored. In this instance, the measured flow rate is compared to a threshold flow range having an upper threshold flow rate and a lower threshold flow rate. If flow to the flow sensor exceeds the upper threshold flow rate this could be indicative of a heat event or sampling pipe breakage, as described above. If flow to the flow sensor decreases to below the lower threshold flow rate this could be indicative of a blockage in a sampling pipe and/or one or more sampling inlets. If the measured flow rate is below the lower threshold flow rate a signal is generated indicating a flow fault, potentially due to pipe and/or inlet blockage, and action may be taken to rectify the flow fault.

(24) It will be appreciated that the use of heat activated sampling points in conjunction with conventional sampling points of an aspirated smoke detector allows the present invention to be used in environments where it is desirable to distinctly monitor heat events, smoke events, and heat and smoke events.

(25) It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.