Fire alarm

Abstract

To provide a fire alarm device capable of restricting a person in a fire site from failing in escape.SOLUTION: A fire alarm device 1 includes: a CO sensor 2 for detecting a carbon monoxide concentration contained in an environment atmosphere; and a smoke sensor 3 for detecting a smoke concentration contained in the environment atmosphere. The fire alarm device 1 issues alarm when the smoke concentration to be detected by the smoke sensor 3 exceeds a predetermined smoke alarm threshold. The fire alarm device 1 calculates a carbon monoxide hemoglobin concentration in blood from the carbon monoxide concentration to be detected by the CO sensor 2, and reduces the smoke alarm threshold when the carbon monoxide hemoglobin concentration to be calculated exceeds a predetermined carbon monoxide hemoglobin concentration threshold.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fire alarm. [Background technology]

[0002] As stipulated in the "Ministry Ordinance on Technical Standards for Residential Fire Alarms and Residential Fire Alarm Systems," fire alarms for detecting fires must be configured to sound an alarm when the detected smoke concentration exceeds a certain smoke alarm threshold. The smoke alarm thresholds to be adopted are set by ministerial ordinance, such as 5% / m (Type 1) and 10% / m (Type 2). In order to detect a fire as early as possible and ensure personal safety, it is desirable to adopt a smoke alarm threshold as low as possible, 5% / m (Type 1). However, in the case of fire alarms used for residential use, if a smoke alarm threshold of 5% / m (Type 1) is adopted, there is a high possibility that it will react to even slight smoke such as cigarette smoke or smoke generated during cooking and give a false alarm, so a smoke alarm threshold of 10% / m (Type 2) is generally adopted.

[0003] In order to detect the occurrence of a fire as early as possible, a fire alarm such as that disclosed in Patent Document 1 is used. The fire alarm of Patent Document 1 includes a CO sensor that detects carbon monoxide in addition to a smoke sensor that detects smoke. The fire alarm of Patent Document 1 determines that a fire has occurred and issues an alarm when the detected amounts of smoke and carbon monoxide obtained from the smoke sensor and the CO sensor or the rate of change of the detected amounts exceed a predetermined threshold. When a fire occurs, carbon monoxide is often generated before smoke is generated, and thus the occurrence of a fire can be detected early by detecting not only smoke but also carbon monoxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-277138 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the fire alarm of Patent Document 1, an alarm is issued only when the parameters related to detected smoke and carbon monoxide exceed a predetermined threshold and it is determined that a fire has occurred. However, even if a person at the fire scene is in a situation where it is possible to determine that a fire has occurred and an alarm is issued, it may already be difficult for the person to evacuate. For example, if a person at the fire scene is placed in a situation where a low carbon monoxide concentration that does not allow a fire to be determined is detected for a long time, the carboxyhemoglobin concentration in the blood may increase without a warning of the fire occurrence, and the human body functions may become impaired. In that case, even if an alarm is issued only when it is possible to determine that a fire has occurred, the person at the fire scene may already be in a state of impaired human body functions, and may be late in escaping from the fire scene. It is possible to lower the smoke alarm threshold and carbon monoxide alarm threshold in order to detect the occurrence of a fire early, but blindly lowering the thresholds may lead to the occurrence of false alarms.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a fire alarm that can prevent people at the scene of a fire from being late in escaping. [Means for solving the problem]

[0007] The fire alarm of the present invention is equipped with a CO sensor that detects the concentration of carbon monoxide contained in the environmental atmosphere, and a smoke sensor that detects the concentration of smoke contained in the environmental atmosphere, and is configured to issue an alarm when the smoke concentration detected by the smoke sensor exceeds a predetermined smoke alarm threshold, and is characterized in that the fire alarm is configured to calculate a carboxyhemoglobin concentration in blood from the carbon monoxide concentration detected by the CO sensor, and to lower the smoke alarm threshold when the calculated carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold.

[0008] In addition, the fire alarm is preferably configured to correct the calculated carboxyhemoglobin concentration in accordance with the distance between the expected location of a fire and the location where the fire alarm is installed, and to lower the smoke alarm threshold when the corrected carboxyhemoglobin concentration exceeds the predetermined carboxyhemoglobin concentration threshold.

[0009] In addition, it is preferable that the fire alarm is configured to start calculating the carboxyhemoglobin concentration from the time when the carbon monoxide concentration detected by the CO sensor exceeds a predetermined carbon monoxide threshold value that is lower than a predetermined carbon monoxide alarm threshold value that serves as a criterion for issuing an alarm.

[0010] In addition, it is preferable that the fire alarm is configured to reset the carboxyhemoglobin concentration calculated up to the time when the carbon monoxide concentration detected by the CO sensor remains below a predetermined value for a period exceeding a predetermined time, and to return the lowered smoke alarm threshold to its original value.

[0011] Also, the fire alarm is preferably configured to issue an alarm when the carbon monoxide concentration detected by the CO sensor exceeds a predetermined carbon monoxide alarm threshold. Effect of the Invention

[0012] According to the present invention, a fire alarm that can prevent people at the scene of a fire from being late in escaping can be provided. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram of a fire alarm according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing a schematic view of a room in which a fire alarm according to an embodiment of the present invention is installed; [Diagram 3] 2 is a flow chart illustrating, in a simplified manner, the main steps performed in a fire alarm according to an embodiment of the present invention; [Figure 4]4 is a flow chart illustrating generally the sub-steps performed in a fire alarm according to an embodiment of the invention; [Diagram 5] 4 is a flow chart illustrating generally the sub-steps performed in a fire alarm according to an embodiment of the invention; [Figure 6] 4 is a flow chart illustrating generally the sub-steps performed in a fire alarm according to an embodiment of the invention; [Figure 7] 4 is a flow chart illustrating generally the sub-steps performed in a fire alarm according to an embodiment of the invention; [Figure 8] 4 is a flow chart illustrating generally the sub-steps performed in a fire alarm according to an embodiment of the invention; [Figure 9] 1 is a graph showing the time changes in carbon monoxide concentration, carboxyhemoglobin concentration, and smoke concentration obtained by a fire alarm according to one embodiment of the present invention installed on the ceiling of a room when a futon on the floor of the room was burned by a fire source. [Figure 10] 1 is a graph showing the change over time in carbon monoxide concentration and carboxyhemoglobin concentration obtained by a fire alarm according to one embodiment of the present invention installed on the ceiling and near a fire source in a room when a futon on the floor surface in the room is burned by a fire source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a fire alarm according to an embodiment of the present invention will be described with reference to the accompanying drawings. However, the embodiment described below is merely an example, and the fire alarm of the present invention is not limited to the following example.

[0015] As shown in FIG. 1, the fire alarm 1 of this embodiment includes a CO sensor 2 that detects the concentration of carbon monoxide (CO) contained in the ambient atmosphere, and a smoke sensor 3 that detects the concentration of smoke contained in the ambient atmosphere. The fire alarm 1 is configured to issue an alarm when the smoke concentration detected by the smoke sensor 3 exceeds a predetermined smoke alarm threshold. For example, as shown in FIG. 2, the fire alarm 1 is installed and used in a room R of a house for residential use. However, the fire alarm 1 is not limited to residential use, and can be used for other purposes such as an automatic fire alarm system used in an office or the like. In this embodiment, the fire alarm 1 further includes a control unit 4, a memory unit 5, an alarm unit 6, and a power supply unit 7, as shown in FIG. 1. The fire alarm 1 is configured so that each component is activated by power supply from the power supply unit 7 provided inside. However, the fire alarm 1 may be supplied with power from an external power source.

[0016] The CO sensor 2 detects the carbon monoxide concentration contained in the ambient atmosphere at the location where the fire alarm 1 is installed. In this embodiment, as shown in FIG. 1, the CO sensor 2 is communicatively connected to the control unit 4 and detects the carbon monoxide concentration together with the control unit 4. The CO sensor 2 detects carbon monoxide contained in the ambient atmosphere and transmits an output value corresponding to the carbon monoxide concentration to the control unit 4. The control unit 4 calculates the carbon monoxide concentration from the received output value. In this embodiment, the CO sensor 2 is configured separately from the control unit 4, but may be configured as an integral part of the control unit 4.

[0017] In this embodiment, the CO sensor 2 is an electrochemical gas sensor. The electrochemical gas sensor consumes low power, so the power consumption of the fire alarm 1 can be reduced. Furthermore, when the fire alarm 1 uses a battery as the power supply unit 7, the low power consumption makes it suitable for long-term use. The CO sensor 2, which is an electrochemical gas sensor, detects a current value corresponding to the carbon monoxide concentration by utilizing an oxidation reaction of carbon monoxide, and transmits an output value corresponding to the current value to the control unit 4. However, the CO sensor 2 is not limited to an electrochemical gas sensor as long as it can detect the carbon monoxide concentration in the ambient atmosphere, and may be another gas sensor such as a semiconductor gas sensor or a catalytic combustion gas sensor.

[0018] The smoke sensor 3 detects the smoke concentration contained in the environmental atmosphere in the location where the fire alarm 1 is installed. In this embodiment, as shown in FIG. 1, the smoke sensor 3 is communicatively connected to the control unit 4 and detects the smoke concentration together with the control unit 4. The smoke sensor 3 detects smoke contained in the environmental atmosphere and transmits an output value corresponding to the smoke concentration to the control unit 4. The control unit 4 calculates the smoke concentration from the received output value. In this embodiment, the smoke sensor 3 is configured separately from the control unit 4, but it may also be configured as an integral part of the control unit 4.

[0019] In this embodiment, the smoke sensor 3 is a scattered light type smoke sensor. The smoke sensor 3, which is a scattered light type smoke sensor, includes a light emitting unit and a light receiving unit (not shown). The smoke sensor 3 detects a current value corresponding to the smoke concentration that is generated when the light receiving unit receives scattered light generated when light from the light emitting unit is scattered by smoke particles, and transmits an output value corresponding to the current value to the control unit 4. However, the smoke sensor 3 is not limited to a scattered light type smoke sensor as long as it can detect the smoke concentration contained in the environmental atmosphere, and may be another type of smoke sensor.

[0020] The control unit 4 calculates the carbon monoxide concentration and the smoke concentration based on the output values ​​from the CO sensor 2 and the smoke sensor 3. The control unit 4 also has a calculation processing function for performing the processing described below. As shown in FIG. 1, the control unit 4 is communicatively connected to the CO sensor 2 and the smoke sensor 3, and controls the operation of the CO sensor 2 and the smoke sensor 3, and receives the output values ​​obtained by the CO sensor 2 and the smoke sensor 3. In this embodiment, the control unit 4 is communicatively connected to the storage unit 5 and the alarm unit 6, and is configured to control the operation of each component and to transmit and receive information to each component. The control unit 4 can be configured using, for example, a known central processing unit (CPU).

[0021] The storage unit 5 stores information about carbon monoxide and smoke. As shown in FIG. 1, the storage unit 5 is communicably connected to the control unit 4 and configured to communicate information about carbon monoxide and smoke with the control unit 4. The information about carbon monoxide and smoke here includes, for example, output values ​​from the CO sensor 2 and the smoke sensor 3, carbon monoxide concentration and smoke concentration calculated from output values ​​from the CO sensor 2 and the smoke sensor 3, a relational expression (calibration curve) between the output value of the CO sensor 2 and the carbon monoxide concentration obtained in advance, a relational expression (calibration curve) between the output value of the smoke sensor 3 and the smoke concentration obtained in advance, a carbon monoxide alarm threshold, a smoke alarm threshold, a carboxyhemoglobin (COHb) concentration in blood calculated from the detected carbon monoxide concentration, a carboxyhemoglobin concentration threshold, and the like. The storage unit 5 may also be configured to store programs and calculation formulas capable of executing the processes described below. The storage unit 5 is not particularly limited and can be configured by a known volatile memory such as a RAM, or a known non-volatile memory such as a hard disk or a flash memory.

[0022] The alarm unit 6 issues an alarm when the smoke concentration exceeds a predetermined smoke alarm threshold. The alarm unit 6 may also issue an alarm when the carbon monoxide concentration exceeds a predetermined carbon monoxide alarm threshold. As shown in Fig. 1, the alarm unit 6 is communicatively connected to the control unit 4, and issues an alarm under the control of the control unit 4. The alarm unit 6 is not particularly limited and is composed of an LED light, a speaker, etc., and issues an alarm such as turning on an LED or sounding an alarm.

[0023] Next, the operation of the fire alarm 1 of this embodiment will be described with reference to Figs. 3 to 8. Fig. 3 is a flow chart that shows in outline the main step MS performed by the fire alarm 1. Fig. 4 is a flow chart that shows in outline the sub-step SS1 performed in the main step MS of Fig. 3. Figs. 5 to 8 are flow charts that show in outline the sub-steps SS2 to SS5 that are optionally performed in the sub-step SS1 of Fig. 4. Sub-steps SS2 to SS5 may not be performed, any one of them may be performed, or any two or more of them may be performed in combination. Note that the operations described below are not limited to the order described, and may be performed in an order different from the order described.

[0024] The fire alarm 1 is configured to execute a main step MS as shown in FIG. 3. The fire alarm 1 is configured by the main step MS to issue an alarm when the smoke density detected by the smoke sensor 3 exceeds a predetermined smoke alarm threshold (if the smoke alarm threshold is lowered as described later, the lowered smoke alarm threshold, the same below). In this embodiment, the smoke sensor 3 of the fire alarm 1 detects smoke in the environmental atmosphere and transmits an output value corresponding to the smoke density to the control unit 4 of the fire alarm 1. The control unit 4 receives the output value from the smoke sensor 3 and calculates the smoke density from the output value using a relational expression between the output value and the smoke density stored in the storage unit 5. The fire alarm 1 thereby detects the smoke density (MS1). Next, the control unit 4 judges whether the detected smoke density exceeds the predetermined smoke alarm threshold (MS2). If the smoke density exceeds the predetermined smoke alarm threshold, the control unit 4 activates the alarm unit 6 to issue a fire alarm (MS3). This allows people in the environment where the fire alarm 1 is installed to recognize that there is a possibility of a fire occurring. If the smoke density does not exceed the predetermined smoke alarm threshold, the control unit 4 repeats the process from the beginning of the main step MS. After issuing a fire alarm, the control unit 4 may stop the fire alarm if a predetermined condition is satisfied. The predetermined condition here is not particularly limited, but may be, for example, when the smoke density falls to a predetermined smoke alarm threshold or below, or when the time during which the smoke density is below the predetermined smoke alarm threshold exceeds a predetermined time. When the control unit 4 stops the fire alarm, it performs the main step MS as usual. The fire alarm 1 may be configured to store the detected smoke density in chronological order.

[0025] The smoke alarm threshold here refers to the smoke density that is the standard for determining whether a fire may have occurred. The predetermined smoke alarm threshold is not particularly limited, and can be set appropriately according to the smoke density at which it can be determined that a fire has occurred in the environment in which the fire alarm 1 is installed. The predetermined smoke alarm threshold can be set, for example, to 10% / m, which is defined as the second type in the "Ministry Ordinance Prescribing Technical Standards for Residential Fire Alarms and Residential Fire Alarm Systems."

[0026] As shown in FIG. 3, the fire alarm 1 is configured to perform sub-step SS1 in the above-mentioned main step MS. As shown in FIG. 4, the fire alarm 1 is configured to calculate the carboxyhemoglobin concentration in blood from the carbon monoxide concentration detected by the CO sensor 2 in sub-step SS1, and to lower the smoke alarm threshold when the calculated carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold. In this embodiment, the CO sensor 2 of the fire alarm 1 detects carbon monoxide in the environmental atmosphere and transmits an output value corresponding to the carbon monoxide concentration to the control unit 4 of the fire alarm 1. The control unit 4 receives the output value from the CO sensor 2 and calculates the carbon monoxide concentration from the output value using a relational expression between the output value and the carbon monoxide concentration stored in the storage unit 5. The fire alarm 1 thereby detects the carbon monoxide concentration (SS11). Here, the fire alarm 1 may be configured to store the detected carbon monoxide concentrations in chronological order. In this embodiment, the control unit 4 transmits the calculated carbon monoxide concentration to the storage unit 5, and the storage unit 5 stores the carbon monoxide concentration together with the elapsed time from the start of measurement (SS12). Next, the control unit 4 calculates the carboxyhemoglobin concentration in the human blood from the detected carbon monoxide concentration (SS13). The control unit 4 determines whether the calculated carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold (SS14). If the carboxyhemoglobin concentration exceeds the predetermined carboxyhemoglobin concentration threshold, the control unit 4 lowers the smoke alarm threshold (SS15) and ends sub-step SS1. On the other hand, if the carboxyhemoglobin concentration does not exceed the predetermined carboxyhemoglobin concentration threshold, the control unit 4 ends sub-step SS1. At this time, if the smoke alarm threshold has already been lowered, the control unit 4 returns the lowered smoke alarm threshold to its original value. After the control unit 4 ends sub-step SS1, it performs the process following the main step MS described above.

[0027] The carboxyhemoglobin concentration referred to here is the concentration of carboxyhemoglobin estimated to be produced in the blood of a human being when the human being is present in the environment in which the fire alarm 1 is installed. The carboxyhemoglobin concentration can be calculated (estimated) according to the time the human being is exposed to carbon monoxide and the carbon monoxide concentration at that time. The carboxyhemoglobin concentration is not particularly limited, and can be calculated, for example, from the experimentally or empirically obtained relationship between the carbon monoxide concentration and the exposure time and the carboxyhemoglobin concentration in the human blood, or can be calculated using a known formula reported in "Dangers of Combustion (Oxygen-Deficient Combustion) in a Room with Low Ventilation Rate of Domestic Gas Appliances" (Safety Engineering Vol. 19 No. 4 (1980)), or can be calculated using a newly created formula based on such a known formula. When using the above formula to calculate the carboxyhemoglobin concentration, the oxygen concentration contained in the environmental atmosphere is also required, and in this case, the oxygen concentration normally present in the air or the oxygen concentration detected by an oxygen sensor optionally provided in the fire alarm 1 may be used as the oxygen concentration.

[0028] The carboxyhemoglobin concentration threshold here is a carboxyhemoglobin concentration that is a standard for determining that a person in the environment in which the fire alarm 1 is installed has a functional impairment that may hinder the person from escaping from the environment. The predetermined carboxyhemoglobin concentration threshold is not particularly limited, and can be set appropriately according to the carboxyhemoglobin concentration at which it can be determined that a person's functional impairment is occurring. In general, it is said that a carboxyhemoglobin concentration exceeding 10% causes a mild headache and dilation of subcutaneous blood vessels, a carboxyhemoglobin concentration exceeding 20% ​​causes a headache and pulsation in the side of the head, and a carboxyhemoglobin concentration exceeding 30% causes a severe headache, dizziness, blurred vision, vomiting, and a pink-red coloring of the lips and mucous membranes. The predetermined carboxyhemoglobin concentration threshold can be set to, for example, 10% at which a mild headache and dilation of subcutaneous blood vessels occur, taking into consideration a functional decline that may hinder a person from escaping from the environment in which the fire alarm 1 is installed.

[0029] Also, lowering the smoke alarm threshold here means resetting the smoke alarm threshold to a value lower than the preset smoke alarm threshold. The reset smoke alarm threshold is not particularly limited as long as it is at least lower than the preset smoke alarm threshold, but for example, it can be set to 5% / m, which is defined as a type in the "Ministry Ordinance on Technical Standards for Residential Fire Alarms and Residential Fire Alarm Systems."

[0030] As described above, the fire alarm 1 is configured to set a smoke alarm threshold lower than a preset smoke alarm threshold when the carboxyhemoglobin concentration calculated from the carbon monoxide concentration exceeds a predetermined carboxyhemoglobin concentration threshold, and to issue an alarm when the smoke concentration exceeds the lower smoke alarm threshold. Therefore, people in the environment (fire scene) in which the fire alarm 1 is installed can recognize the occurrence of a fire and begin to escape when the smoke concentration is relatively low even if they are in a state where functional impairment may occur, thereby preventing people from being late in escaping from the fire scene. In addition, by lowering the smoke alarm threshold only when there is a high possibility that the human function is impaired, the accuracy of fire detection can be improved while preventing the occurrence of false alarms.

[0031] Here, a specific example of the main step MS including the above-mentioned sub-step SS1 will be described with reference to FIG. 9. FIG. 9 shows the time changes of the carbon monoxide concentration, the carboxyhemoglobin concentration, and the smoke concentration obtained by the fire alarm 1 installed on the ceiling C when a futon D on a floor surface F is burned by a fire source (heater) H in a room R as shown in FIG. 2 to cause a smoldering fire. Referring to FIG. 9, it can be seen that the carbon monoxide concentration starts to rise about 15 minutes after the start of driving the fire source H, and the carboxyhemoglobin concentration also starts to rise accordingly. On the other hand, the smoke concentration starts to rise about 50 minutes after the start of driving the fire source H. For example, if the preset smoke alarm threshold is 10% / m, and the above-mentioned sub-step SS1 is not performed, the smoke concentration will exceed the smoke alarm threshold and an alarm will be issued about 74 minutes after the start of driving the fire source H. For example, when the carboxyhemoglobin concentration threshold is set to 10% and the above-mentioned sub-step SS1 is performed, the carboxyhemoglobin concentration exceeds the carboxyhemoglobin concentration threshold and the smoke alarm threshold is lowered about 54 minutes after the start of driving the fire source H. For example, when the lowered smoke alarm threshold is set to 5% / m, the smoke concentration exceeds the already lowered smoke alarm threshold about 70 minutes after the start of driving the fire source H, and an alarm is issued at this point. In other words, according to the fire alarm 1 of this embodiment, when there is a possibility that the function of a person is impaired, an alarm is issued about 4 minutes earlier than usual. As a result, a person in the environment (fire scene) where the fire alarm 1 is installed can recognize the occurrence of a fire and start to escape at a stage when the smoke concentration is low, even if the person is in a state where functional impairment may occur, so that a delay in escaping from the fire scene is suppressed.

[0032] As described above, the fire alarm 1 may be configured to perform one or more of the sub-steps SS2 to SS5 in the sub-step SS1 of the main step MS. For example, the fire alarm 1 may be configured to perform the sub-step SS2 in the sub-step SS1 as shown in FIG. 4. The fire alarm 1 is configured to issue an alarm in the sub-step SS2 when the carbon monoxide concentration detected by the CO sensor 2 exceeds a predetermined carbon monoxide alarm threshold as shown in FIG. 5. In this embodiment, as shown in FIG. 4, the fire alarm 1 detects the carbon monoxide concentration in the sub-step SS1 (SS11). Next, as shown in FIG. 5, the control unit 4 of the fire alarm 1 determines whether or not the detected carbon monoxide concentration exceeds a predetermined carbon monoxide alarm threshold in the sub-step SS2 (SS21). When the carbon monoxide concentration exceeds the predetermined carbon monoxide alarm threshold, the control unit 4 activates the alarm unit 6 to issue a CO alarm (SS22). This allows people in the environment where the fire alarm 1 is installed to recognize that a fire may have occurred. For example, in cases where no flame occurs, such as in a smoldering fire, smoke may occur significantly later than the generation of carbon monoxide (see, for example, FIG. 9). Even in such cases, people in the environment where the fire alarm 1 is installed can recognize the fire early because an alarm is issued when the carbon monoxide concentration exceeds a predetermined carbon monoxide alarm threshold. If the carbon monoxide concentration does not exceed the predetermined carbon monoxide alarm threshold, the control unit 4 ends sub-step SS2 and performs processing after sub-step SS1. Note that the control unit 4 may stop the CO alarm when a predetermined condition is satisfied after issuing a CO alarm. The predetermined condition here is not particularly limited, but may be, for example, when the carbon monoxide concentration falls to a predetermined carbon monoxide alarm threshold or less, or when the time during which the carbon monoxide concentration is below the predetermined carbon monoxide alarm threshold exceeds a predetermined time. When the control unit 4 stops the CO alarm, it ends sub-step SS2 and performs processing after sub-step SS1.

[0033] The carbon monoxide alarm threshold here refers to a carbon monoxide concentration that is a criterion for determining that a fire may have occurred. The predetermined carbon monoxide alarm threshold is not particularly limited, and can be set appropriately according to the carbon monoxide concentration at which it can be determined that a fire has occurred in the environment in which the fire alarm 1 is installed. The predetermined carbon monoxide alarm threshold can be set to, for example, 100 ppm.

[0034] The fire alarm 1 may be configured to perform sub-step SS3 in sub-step SS1 as shown in Fig. 4. The fire alarm 1 is configured to start calculating the carboxyhemoglobin concentration from the time point when the carbon monoxide concentration detected by the CO sensor 2 exceeds a predetermined carbon monoxide threshold in sub-step SS3 as shown in Fig. 6. In this embodiment, the fire alarm 1 detects the carbon monoxide concentration in sub-step SS1 as shown in Fig. 4 (SS11). Next, the control unit 4 of the fire alarm 1 determines whether the calculation process of the carboxyhemoglobin concentration is continuing or not in sub-step SS3 as shown in Fig. 6 (SS31). That is, the control unit 4 determines whether the calculation process of the carboxyhemoglobin concentration was performed at the time of the previous carbon monoxide concentration detection or not. If the calculation process of the carboxyhemoglobin concentration is ongoing, the control unit 4 ends the sub-step SS3 and performs the process after the sub-step SS1 (calculation process of the carboxyhemoglobin concentration). If the calculation process of the carboxyhemoglobin concentration is not ongoing, the control unit 4 determines whether or not the detected carbon monoxide concentration exceeds a predetermined carbon monoxide threshold (SS32). If the carbon monoxide concentration exceeds the predetermined carbon monoxide threshold, the control unit 4 ends the sub-step SS3 and performs the process after the sub-step SS1 (calculation process of the carboxyhemoglobin concentration). By starting the calculation process of the carboxyhemoglobin concentration at the time when the carbon monoxide concentration exceeds the predetermined carbon monoxide threshold in this way, it is possible to eliminate measurement data of the carbon monoxide concentration that does not substantially affect the increase in the carboxyhemoglobin concentration, and thereby it is possible to calculate the carboxyhemoglobin concentration with high accuracy. If the carbon monoxide concentration does not exceed the predetermined carbon monoxide threshold, the control unit 4 ends the sub-step SS1 and performs the process after the main step MS.

[0035] The carbon monoxide threshold here is a carbon monoxide concentration that is a criterion for determining whether there is a possibility of affecting an increase in the carboxyhemoglobin concentration in human blood. The predetermined carbon monoxide threshold is not particularly limited, and can be set appropriately according to a carbon monoxide concentration that can be determined to have a possibility of affecting an increase in the carboxyhemoglobin concentration in human blood. The predetermined carbon monoxide threshold can be set to a value lower than a predetermined carbon monoxide alarm threshold that is a criterion for issuing an alarm, for example, 50 ppm.

[0036] The fire alarm 1 may be configured to perform sub-step SS4 in sub-step SS1 as shown in FIG. 4. The fire alarm 1 is configured to set the carboxyhemoglobin concentration calculated up until the time when the carbon monoxide concentration detected by the CO sensor 2 is equal to or lower than a predetermined value to zero and to return the lowered smoke alarm threshold to its original value in sub-step SS4 as shown in FIG. 7, when the duration during which the carbon monoxide concentration detected by the CO sensor 2 is equal to or lower than a predetermined value exceeds a predetermined time. In this embodiment, the fire alarm 1 detects the carbon monoxide concentration in sub-step SS1 as shown in FIG. 4 (SS11). Next, the control unit 4 of the fire alarm 1 determines whether the carbon monoxide concentration is equal to or lower than a predetermined value in sub-step SS4 as shown in FIG. 7 (SS41). If the carbon monoxide concentration is equal to or lower than the predetermined value, the control unit 4 performs the following further processing, and if the carbon monoxide concentration exceeds the predetermined value, ends sub-step SS4 and performs processing after sub-step SS1. When the carbon monoxide concentration is equal to or less than the predetermined value, the control unit 4 judges whether or not the duration during which the carbon monoxide concentration is equal to or less than the predetermined value exceeds a predetermined time (SS42). When the duration exceeds the predetermined time, the control unit 4 sets the carboxyhemoglobin concentration calculated up until the time when the predetermined time has elapsed to zero, and when the smoke alarm threshold has been lowered at the time when the predetermined time has elapsed, returns the smoke alarm threshold to its original value (SS43). Then, the control unit 4 ends the sub-step SS1 and performs processing after the main step MS. On the other hand, when the duration during which the carbon monoxide concentration is equal to or less than the predetermined value does not exceed the predetermined time, the control unit 4 ends the sub-step SS4 and performs processing after the sub-step SS1. When the duration during which the carbon monoxide concentration is equal to or less than the predetermined value exceeds the predetermined time, it is highly likely that the carboxyhemoglobin concentration in the human blood has decreased. In such a case, by setting (resetting) the carboxyhemoglobin concentration to zero, the carboxyhemoglobin concentration in the human blood can be calculated (estimated) with higher accuracy when the carbon monoxide concentration rises again. In addition, if the smoke alarm threshold has been lowered, the occurrence of false alarms can be reduced by returning the smoke alarm threshold to its original value.

[0037] The predetermined value for the carbon monoxide concentration is a carbon monoxide concentration that is a criterion for determining that the concentration does not affect the increase in the carboxyhemoglobin concentration in human blood. The predetermined value is not particularly limited, and can be set appropriately according to a carbon monoxide concentration that can be determined not to affect the increase in the carboxyhemoglobin concentration in human blood. The predetermined value can be set to a value lower than a predetermined carbon monoxide alarm threshold that is a criterion for issuing an alarm, and more specifically, can be set to 10 ppm, which is the carbon monoxide concentration standard in indoor air in the Building Environmental Sanitation Management Standards.

[0038] The predetermined time for the duration during which the carbon monoxide concentration is equal to or lower than the predetermined value is a reference time when it is assumed that the carboxyhemoglobin concentration in the human blood has recovered (decreased) to a level at which the functional impairment of the human does not occur. The predetermined time is not particularly limited, and can be set appropriately according to the time at which it can be assumed that the carboxyhemoglobin concentration in the human blood has recovered (decreased) to a level at which the functional impairment of the human does not occur. The predetermined time can be set, for example, to several minutes to several hours (for example, 3 to 4 hours when the half-life of carboxyhemoglobin is used).

[0039] The fire alarm 1 may be configured to correct the calculated carboxyhemoglobin concentration according to the distance between the expected fire occurrence location and the installation location where the fire alarm is installed. Then, the fire alarm 1 may be configured to lower the smoke alarm threshold when the corrected carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold. In this embodiment, the control unit 4 of the fire alarm 1 determines whether the calculated carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold in sub-step SS1 as shown in FIG. 4 (SS14). Instead of this process SS14, the control unit 4 performs sub-step SS5 shown in FIG. 8. In sub-step SS5, the control unit 4 corrects the calculated carboxyhemoglobin concentration according to the distance between the expected fire occurrence location and the installation location where the fire alarm is installed (SS51). Then, the control unit 4 determines whether the corrected carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold (SS52). If the corrected carboxyhemoglobin concentration exceeds the predetermined carboxyhemoglobin concentration threshold, the control unit 4 ends substep SS5 and returns to substep SS1, lowering the smoke alarm threshold (SS15).If the corrected carboxyhemoglobin concentration does not exceed the predetermined carboxyhemoglobin concentration threshold, the control unit 4 returns the corrected carboxyhemoglobin concentration to the original carboxyhemoglobin concentration, ends substep SS1, and performs processing after main step MS.

[0040] Here, the fire alarm 1 is generally installed on the ceiling or wall of a room. In contrast, the location of a fire is often the floor or its surroundings, such as a fire caused by improper cigarette disposal. The carbon monoxide concentration near the location of the fire may be higher than the carbon monoxide concentration near the ceiling or wall, which is a location away from the location of the fire. Accordingly, the carboxyhemoglobin concentration in the blood of a person near the location of the fire may be higher than the carboxyhemoglobin concentration calculated based on the carbon monoxide concentration detected at a location away from the location of the fire. For example, FIG. 10 shows the difference in the time change of the carbon monoxide concentration and the carboxyhemoglobin concentration due to the difference in the installation location between the fire alarm 1 installed near the fire source H and the fire alarm 1 installed on the ceiling C as shown in FIG. 2. In the fire alarm 1 installed near the fire source H, the time when carbon monoxide begins to be detected is earlier and the detected carbon monoxide concentration is higher than the fire alarm 1 installed on the ceiling C, which is away from the fire source H. Accordingly, the carboxyhemoglobin concentration near the fire source H starts to rise earlier and is higher than the carboxyhemoglobin concentration near the ceiling C. In this way, if a fire alarm is installed at a position away from the fire outbreak location, the carboxyhemoglobin concentration in the blood of people near the fire outbreak location may be calculated (estimated) to be lower. In response to this, as described above, the carboxyhemoglobin concentration in the blood of people near the fire outbreak location can be more accurately estimated by correcting the calculated carboxyhemoglobin concentration according to the distance between the expected fire outbreak location and the installation location of the fire alarm. Then, by changing the smoke alarm threshold based on the corrected carboxyhemoglobin concentration, a fire alarm can be issued more accurately, and the delay in escaping by people near the fire outbreak location can be more reliably prevented.

[0041] The carbon monoxide concentration is corrected based on the distance between the expected fire occurrence location and the installation location where the fire alarm is installed. For example, it is known that the carbon monoxide concentration changes depending on the horizontal and vertical distances from the fire occurrence location when a fire occurs in a room. Therefore, the carbon monoxide concentration can be corrected depending on the horizontal and vertical distances between the expected fire occurrence location and the installation location where the fire alarm is installed. For example, a correction formula for correcting the carbon monoxide concentration can be obtained from the relationship between the carbon monoxide concentration at the actual fire occurrence location (or its vicinity) and the carbon monoxide concentration at the installation location where the fire alarm 1 is installed, which is obtained experimentally or empirically. The correction formula can also be constant with respect to the distance when the distance between the expected fire occurrence location and the installation location where the fire alarm is installed is within a certain range. In addition, in this embodiment, when correcting the carboxyhemoglobin concentration, the distance between the expected location of the fire and the installation location where the fire alarm is installed is used, but the distance between the actual location of the fire determined from a thermal sensor or the like and the installation location where the fire alarm is installed may also be used.

[0042] In this embodiment, the calculated carboxyhemoglobin concentration is corrected in sub-step SS5. However, the same effect as above can be achieved even if the carboxyhemoglobin concentration threshold is corrected instead of the calculated carboxyhemoglobin concentration. In addition, the change from the judgment process SS14 in sub-step SS1 to sub-step SS5 can be performed, for example, by switching using a switch provided in the fire alarm 1 when the fire alarm 1 is installed. [Explanation of symbols]

[0043] 1 Fire alarm 2 CO sensor 3 Smoke Sensor 4. Control section 5 Storage section 6 Alarm section 7 Power supply section C Ceiling D. Futon F Floor H Fire source MS Main Step Room R SS1, SS2, SS3, SS4, SS5 substeps

Claims

1. A CO sensor is provided for detecting a carbon monoxide concentration in the environmental atmosphere, and a smoke sensor is provided for detecting a smoke concentration in the environmental atmosphere, A fire alarm configured to issue an alarm when a smoke density detected by the smoke sensor exceeds a predetermined smoke alarm threshold, The fire alarm is configured to calculate a carboxyhemoglobin concentration in blood from the carbon monoxide concentration detected by the CO sensor, and to lower the smoke alarm threshold when the calculated carboxyhemoglobin concentration exceeds a predetermined carboxyhemoglobin concentration threshold. Fire alarm.

2. The fire alarm is configured to correct the calculated carboxyhemoglobin concentration according to a distance between an assumed location of a fire and a location where the fire alarm is installed, and to lower the smoke alarm threshold when the corrected carboxyhemoglobin concentration exceeds the predetermined carboxyhemoglobin concentration threshold.

2. The fire alarm of claim 1.

3. The fire alarm is configured to start calculating the carboxyhemoglobin concentration when the carbon monoxide concentration detected by the CO sensor exceeds a predetermined carbon monoxide threshold value that is lower than a predetermined carbon monoxide alarm threshold value that is a criterion for issuing an alarm.

3. A fire alarm according to claim 1 or 2.

4. The fire alarm is configured to reset the carboxyhemoglobin concentration calculated up to the time when the carbon monoxide concentration detected by the CO sensor is equal to or lower than a predetermined value for a duration exceeding a predetermined time, and to return the lowered smoke alarm threshold to its original value. A fire alarm according to any one of claims 1 to 3.

5. The fire alarm is configured to issue an alarm when a carbon monoxide concentration detected by the CO sensor exceeds a predetermined carbon monoxide alarm threshold. A fire alarm according to any one of claims 1 to 4.

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