FIRE DETECTION SYSTEM AND METHOD FOR IDENTIFYING A SOURCE OF SMOKE IN A MONITORED ENVIRONMENT

Abstract

A fire detection system for monitoring a monitored environment includes a smoke detector configured to determine a concentration of smoke in a sample of air from the monitored environment; a gas sensor configured to determine a concentration of a predetermined gas in the sample of air, the predetermined gas is one of carbon monoxide, carbon dioxide, nitrogen dioxide and sulphur dioxide; and a control module in communication with the smoke detector and the gas sensor; the control module is configured to identify a source of the smoke based on the concentration of smoke and the concentration of the predetermined gas; and the source of the smoke is identified to be a non-fire source when the concentration of the predetermined gas in the sample of air is below a first threshold.

Claims

1. A fire detection system (1) for monitoring a monitored environment (100), the system comprising: a smoke detector (3) configured to determine a concentration of smoke in a sample of air from the monitored environment (100); a gas sensor (2) configured to determine a concentration of a predetermined gas in the sample of air, wherein the predetermined gas is one of carbon monoxide, carbon dioxide, nitrogen dioxide and sulphur dioxide; and a control module (4) in communication with the smoke detector (3) and the gas sensor (2); wherein the control module (4) is configured to identify a source of the smoke based on the concentration of smoke and the concentration of the predetermined gas; and wherein the source of the smoke is identified to be a non-fire source when the concentration of the predetermined gas in the sample of air is below a first threshold.

2. A fire detection (1) system as claimed in claim 1, wherein the control module (4) is configured to compare the concentration of smoke and the concentration of the predetermined gas to predetermined concentrations associated with a plurality of known smoke sources; and wherein the control module (4) is configured to select one of the plurality of known smoke sources as the source of the smoke based on the comparison.

3. A fire detection system (1) as claimed in claim 1, wherein the source of the smoke is identified to be a fire source when the concentration of the predetermined gas in the sample of air exceeds the first threshold.

4. A fire detection system (1) as claimed in claim 1, wherein the source of the smoke is identified to be: an organic fire source when the concentration of the predetermined gas in the sample of air exceeds the first threshold and does not exceed a second threshold, wherein the first threshold is less than the second threshold; or a liquid fuel fire source when the concentration of the predetermined gas in the sample of air exceeds the second threshold and does not exceed a third threshold, wherein the second threshold is less than the third threshold; or a synthetic fire source when the concentration of the predetermined gas in the sample of air exceeds the third threshold.

5. A fire detection system (1) as claimed in claim 1, wherein the control module (4) is configured to generate an alarm signal based on the identified source of the smoke.

6. A fire detection system (1) according to claim 1, wherein the fire detection system (1) is an aspirating fire detection system.

7. A method of determining a source of smoke in a monitored environment (100), the method comprising: determining a concentration of smoke in a sample of air from the monitored environment (100); determining a concentration of a predetermined gas in the sample of air, wherein the predetermined gas is one of carbon monoxide, carbon dioxide, nitrogen dioxide or sulphur dioxide; and identifying a source of the smoke based on the concentration of smoke and the concentration of the predetermined gas; wherein the source of the smoke is identified to be a non-fire source when the concentration of the predetermined gas in the sample of air does not exceed a first threshold.

8. A method as claimed in claim 7, the method comprising: comparing the concentration of smoke and the concentration of the predetermined gas to predetermined concentrations associated with a plurality of known smoke sources; and selecting one of the plurality of known smoke sources as the source of the smoke based on the comparison.

9. A method as claimed in claim 7, wherein the source of the smoke is identified to be a fire source when the concentration of the predetermined gas in the sample of air exceeds the first threshold.

10. A method as claimed in claim 7, the method comprising: comparing the concentration of the predetermined gas in the sample of air to each of: the first threshold, a second threshold greater than the first threshold but less than a third threshold, and the third threshold; wherein the source of the smoke is identified to be: an organic fire source when the concentration of the predetermined gas in the sample of air exceeds the first threshold and does not exceed the second threshold; or a liquid fuel fire source when the concentration of the predetermined gas in the sample of air exceeds the second threshold and does not exceed the third threshold; or a synthetic fire source when the concentration of the predetermined gas in the sample of air exceeds the third threshold.

11. A method as claimed in claim 7, the method comprising: generating an alarm signal based on the source of the smoke.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Certain exemplary embodiments of the disclosure will now be described by way of example only and with reference to the accompanying drawings in which:

[0105] FIG. 1 shows a schematic diagram of a fire detection system;

[0106] FIG. 2A shows a cross-sectional view of a central detection unit of the fire detection system;

[0107] FIG. 2B shows a perspective, cutaway view of the central detection unit of fire detection system shown in FIG. 2A;

[0108] FIGS. 3A to 3C show graphs of how a concentration of smoke in a sample of air and how a concentration of carbon monoxide in a sample of air changes over time during combustion of various compounds; and

[0109] FIG. 4 shows a graph comparing how a concentration of carbon monoxide in a sample of air varies versus a concentration of smoke in a sample of air for various compounds.

DETAILED DESCRIPTION

[0110] FIG. 1 shows a schematic diagram of an aspirating fire detection system 1 monitoring an environment 100. The fire detection system 1 includes a central detection unit 5 connected to a sampling pipe 8. The sampling pipe 8 is exposed to the monitored environment 100 via a plurality of sampling holes 9 in the sample pipe 8, such that the central detection unit 5 is in fluid communication with the monitored environment 100. The central detection 5 is in wired and/or wireless communication with a control module 4. The control module 4 is also in wired and/or wireless communication with an alarm system 101 and a fire mitigation device 102, both of which are present in the monitored environment 100.

[0111] The central detection unit 5 includes an inlet 6 which is connected to the sampling pipe 8. The central detection unit 5 also includes a gas sensor 2, a smoke detector 3 and an outlet 7. Air is aspirated into the central detection unit 5 using an aspirator (not shown), which draws a sample of air from the monitored environment through the sampling pipe 8 and into the central detection unit 5 via the inlet 6. The sampled air is passed to each of the gas sensor 2 and the smoke detector 3. The sampled air is then exhausted from the central detection unit 5 via the outlet 7. The flow of air through the central detection unit 5 is generally indicated by the arrows shown in FIG. 1.

[0112] FIGS. 2A and 2B illustrate the central detection unit 5 of the fire detection system 1. The gas sensor 2 and the smoke detector 3 are housed within a housing of the central detection unit 5.

[0113] The arrows in FIG. 2A indicate a general flow of the air sampled through the housing of the central detection unit 5. Aspirated air is motivated into the central detection unit 5 due to the rotation of an impeller of the aspirator (not shown). The aspirated air is then passed to the gas sensor 2 and the smoke detector 3, before being exhausted from the housing via the outlet 7. Whilst not illustrated in the present embodiment, not all of the air is necessarily passed through both the smoke detector 3 and/or the gas sensor 2. The air may be split such that different portions of the sampled air are passed to each of the smoke detector 3 and the gas sensor 2. Optionally a bypass flow may be present, such that a portion of the sampled air is not passed through the smoke detector 3 and/or the gas sensor 2, for example if the flow rate of the aspirator is greater than the flow rates that can be effectively processed by the smoke detector 3 and/or the gas sensor 2.

[0114] The smoke detector 3 is configured to determine a concentration of smoke in a sample of air from the environment 100 which the fire detection system 1 monitors. The smoke detector 3 in the illustrated embodiment is an optical smoke detector and comprises a detection chamber into which the sample of air is passed, a laser which is shone through the detection chamber, and a photodiode. If smoke is present in the detection chamber, the laser light will be scattered. The photodiode detects the scattered light such that an amount of scattered light can be measured. By measuring an amount of scattered light from the laser, a concentration of smoke present in the sample of air can be determined.

[0115] The fire detection system 1 is employed to detect a fire. The fire detection system 1 primarily does this by detecting smoke in the monitored environment 100 using the smoke detector 3. However, the smoke detector 3 may detect smoke from non-fire sources which are expected to be present in the monitored environment 100, such as cooking sources. The smoke from a cooking source may be indistinguishable from smoke from fire sources against which action should be taken. As such, detecting smoke using the smoke detector 2 alone is not sufficient to distinguish between non-fire, or nuisance, sources and fire sources.

[0116] Different sources of smoke produce different amounts of certain gases during combustion. Gases produced during combustion commonly include carbon monoxide, carbon dioxide, nitrogen dioxide and sulphur dioxide. In the present embodiment, the gas sensor 2 is provided to determine a concentration of carbon monoxide in the sample of air from the monitored environment 100.

[0117] Cooking sources and the like produce lower amounts of carbon monoxide during combustion than other common fire sources. As such determining the concentration of carbon monoxide using the gas sensor 2 and comparing the concentration to a threshold value at which fire sources produce quantities of carbon monoxide enables the fire detection system 1 to be able to discriminate between non-fire sources and fire sources, upon initially detecting the source of smoke using the smoke detector 3.

[0118] By being able to differentiate between non-fire sources and fire sources, alarms relating to the detection of smoke may only be raised by the fire detection system 1 when a fire source is detected. This reduces the incidence of nuisance alarms, and increase the reliability of the fire detection system 1.

[0119] The measurements of the concentration of smoke in the sample of air, determined by the smoke detector 3, and the concentration of carbon monoxide in the sample of air, determined by the gas sensor 2, are passed to the control module 4. Based on the concentration of smoke and the concentration of carbon monoxide in the sample of air, the control module 4 is configured to identify the source of the smoke. The criteria used by the control module 4 in identifying the source of the smoke based on the concentration of smoke and the concentration of carbon monoxide in the sample of air are discussed in further detail below.

[0120] FIGS. 3A to 3C illustrate graphs of how a relative concentration of smoke (%) in a sample of air determined by the smoke detector 3 and the concentration of carbon monoxide (ppm) in the sample of air, determined by the gas sensor 2, varied with time for a plurality of different sources of smoke in test conditions. A 60% relative concentration of smoke in the sample of air is equivalent to an obscuration of 3% obs/m.

[0121] FIG. 3A shows how the relative concentration of smoke and the concentration of carbon monoxide determined varies for non-smouldering polyurethane, i.e. polyurethane that has not been treated by any flame retardants and hence combusts with a flame, in test conditions. As can be seen in FIG. 3A, a peak relative concentration of smoke is determined as approximately 58% and a peak concentration of carbon monoxide is determined as approximately 10 ppm. The graph for non-smouldering polyurethane is exemplary for most synthetic materials which have not been treated with fire retardants.

[0122] FIG. 3B shows how the relative concentration of smoke and the concentration of carbon monoxide determined varies for smouldering wood, i.e. wood that burns without a flame, in test conditions. As can be seen in FIG. 3B, a peak relative concentration of smoke is determined to be approximately 64% and a peak concentration of carbon monoxide is determined to be approximately 8. The graph for smouldering wood is exemplary for most organic materials.

[0123] FIG. 3C shows how the relative concentration of smoke and the concentration of carbon monoxide determined varies for a cooking nuisance, in test conditions. As can be seen in FIG. 3C, a peak relative concentration of smoke is determined to be approximately 46% and a concentration of carbon monoxide is not effectively registered, i.e. the concentration of carbon monoxide produced is negligible. The graph for the cooking nuisance is exemplary for most other cooking sources, or other nuisance sources.

[0124] FIG. 4 shows how the measured concentration of carbon monoxide in a sample of air (y-axis) correlates to the measured relative concentration of smoke in the sample of air (x-axis) in test conditions for each of the three examples shown in FIGS. 3A to 3C, namely cooking nuisance, smouldering wood and non-smouldering polyurethane.

[0125] As can be seen from the graphs shown in FIGS. 3A to 3C and FIG. 4, in the tests each source produces a detectable relative concentration of smoke. However, the concentration of carbon monoxide measured for each source differs. In particular, there is a significant difference in the amount of carbon monoxide produced by a cooking nuisance source compared to smouldering wood and/or non-smouldering polyurethane during combustion. There is a different rate of change with respect to time of the determined concentration of carbon monoxide in the sample of air and a different rate of change with respect to time of the determined relative concentration of smoke in the sample of air for each source (see FIGS. 3A to 3C). There is a different determined concentration of carbon monoxide in the sample of air relative to the determined relative concentration of smoke in the sample of air for each source (see FIG. 4). There is also a different peak relative concentration of smoke in the sample of air determined for each source, and a different peak concentration of carbon monoxide in the sample of air determined for each source (see FIGS. 3A to 3C and FIG. 4).

[0126] The control module is configured to identify that the source of the smoke is a non-fire source when the concentration of carbon monoxide in the sample of air does not exceed a first carbon monoxide threshold. As such, by determining a concentration of carbon monoxide in the sample of air, the fire detection system 1 is able to discriminate between non-fire sources and fire sources based on the determined concentrations of smoke and carbon monoxide in the sample of air.

[0127] The relative concentration of smoke and the concentration of carbon monoxide produced by the sources shown in FIGS. 3A to 3C and FIG. 4 are a selection of known sources of smoke from a plurality of many known sources. Known sources of smoke may be generally classified based on the concentration of smoke and the concentration of carbon monoxide they produce during combustion. The determined concentrations of smoke and carbon monoxide in the sample of air are compared to these predetermined concentrations, and the source of the smoke is selected as being one of these known sources based on the comparison.

[0128] The control module 4 is configured to compare the concentration of carbon monoxide in the sample of air with one or more carbon monoxide thresholds. As discussed above, if the concentration of carbon monoxide in the sample of air does not exceed the first carbon monoxide threshold, the source of the smoke may be identified as a non-fire source. If the concentration of carbon monoxide in the sample of air exceeds the first carbon monoxide threshold the source of the smoke is identified as a fire source. Further carbon monoxide thresholds and smoke thresholds are also used to further identify what the fire source is. Thresholds dependent on a concentration of carbon monoxide relative to a concentration of smoke are used by the control module 4 to discriminate between fire sources.

TABLE-US-00001 Concentration of carbon monoxide relative to Source of smoke concentration of smoke; [CO]/[smoke] Non-fire source [CO]/[smoke] < first [CO]/[smoke] threshold Organic fire source First [CO]/[smoke] threshold < [CO]/[smoke] < second [CO]/[smoke] threshold Liquid fuel source Second [CO]/[smoke] threshold < [CO]/[smoke] < Third [CO]/[smoke] threshold Synthetic source Third [CO]/[smoke] threshold < [CO]/[smoke]

[0129] Table 1 shows how the source of the smoke may be identified based on the concentration of carbon monoxide in the sample of air relative to the concentration of smoke in the sample of air. The control module 4 determines a concentration of carbon monoxide in the sample of air relative to a concentration of smoke in the sample of air. The control module 4 then compares this value to a number of thresholds. The source of the smoke is identified according to the result of the comparison.

[0130] By basing the identification of the source of the smoke on the concentration of carbon monoxide in the sample of air, the fire detection system 1 can discriminate between various sources of smoke, particularly between non-fire sources and fire sources. By basing the identification of the source of the smoke on the concentration of carbon monoxide in the sample of air relative to the concentration of smoke in the sample of air, the fire detection system 1 can discriminate further between different fire sources, which produce different concentrations of carbon monoxide relative to a concentration of smoke produced during combustion.

[0131] The control module 4 generates an alarm signal according to the source of the smoke identified. The generated alarm signal varies according to the source of the smoke identified, and as such the fire detection system 1 produces different responses according the source of smoke identified. The alarm signal is communicated to the alarm system 101.

[0132] The alarm system 101 includes an aural indicator, such as a siren, bell or the like to alert occupants in the monitored environment 100. The alarm system 102 also comprises a display panel indicating the status of the fire detection system 1. If the source of the smoke is identified to be a non-fire source, the generated alarm signal does not activate the aural indicator, but is acknowledged as a textual message displayed on the display panel. If the source of the smoke is identified to be a fire source, the alarm signal activates the aural indicator so that the occupants of the monitored environment 100 are alerted to the presence of the fire source. The display panel also acknowledges the fire source, and any further indication of what the identified fire source is.

[0133] The generated alarm signal can also activate a fire mitigation device 102 located in the monitored environment 100, such as an automated fire extinguisher or a sprinkler system, when a fire source is identified.

[0134] Whilst the gas sensor 2 has been discussed herein as determining a concentration of carbon monoxide in the sample of air, the gas sensor 2 could be configured to determine a concentration of carbon dioxide, nitrogen dioxide or sulphur dioxide instead. As discussed above, these gases are also commonly emitted by fire sources of smoke, but are typically present only in low concentrations from non-fire sources of smoke.