GB2135801A

GB2135801A - Fire alarm system

Info

Publication number: GB2135801A
Application number: GB08404394A
Authority: GB
Inventors: Yukio Yamauchi; Akira Kitajima; Norio Muroi; Hiromitsu Ishii; Takashi Ono; Tadashi Sugiyama; Yasaburo Adachi
Original assignee: Hochiki Corp
Current assignee: Hochiki Corp
Priority date: 1983-02-24
Filing date: 1984-02-20
Publication date: 1984-09-05
Also published as: GB8404394D0; NO163877B; GB2135801B; DE3405857C2; DE3405857A1; NO163877C; NO840628L; CH652519A5

Abstract

A fire alarm system which detects a change in the physical phenomena of the surroundings caused by the occurrence of a fire, in an analogue form by a detector (1a, 1b... 1n), and samples the detection data periodically by a central signal station (10) to make determination of fire is disclosed. The system comprises an operation unit (11-14) for computing and preestimating a time required to reach a level which is dangerous to the people, based on the detection data sampled periodically; and a comparing means (26) for comparing the computed and preestimated time required to reach said level with a time necessary for escape from a fire spot which means decides that the degree of danger exceeds an allowable level when the time for escape is shorter than the computed and preestimated time.

Description

SPECIFICATION Fire alarm system This invention relates to a fire alarm system and more particularly to a fire alarm which is capable of computing and preestimating, on the basis of analog data, such as a temperature, a density of CO gas, or a density of smoke detected by a fire detector or detectors, a degree of danger which will threaten the people in the near future, so as to give an alarm preliminarily when the estimated degree of danger is above the predetermined level.

In general, conventional fire alarm systems operate in such a manner that the signal station thereof receives an analog fire detection signal transmitted by the fire detector or detectors upon detection of a fire and compares the fire detection signal with the preset threshold level to determine the signal represents a fire when the signal exceeds the preset level, and give an alarm. These systems, however, involve such a problem that it possibly generates an erroneous fire alarm signal by a noise because they generate a fire alarm signal whenever the detection signal is above the preset level.

Therefore, there has been proposed, for example by Japanese Patent Application Publication No.

57-15437, DAS 2,341,087 and Swiss Patent No. 575629, to obviate such a problem, a fire alarm system having a formation as shown in Figure 1A which operates as shown in Figure 1 B.

More specifically, this type of fire alarm system is comprised of fire detectors M11 - Mmn each equipped with signal means for continuously or periodically transmitting signals specifying themselves respectively and signals representing momentary information conditions, and a central signal station Z comprising means for identifying and storing the detector signals which are periodically coilated, a comparing means for confirming a change with time of the conditions of the detectors and a logical operation circuit for obtaining an information decision criterion differentiated from the change with time of signals from one or plural detectors.

This fire alarm system operates as shown in K1 to K4 of Figure 1 B. In the case of K1,the fire characteristic value Uk changes abruptly in a short time for example by thunderbolt, but the time length of the change At is shorter than the observation time period to, so that the detector information condition is decided as being normal and no alarm is given. In the case of K2, the fire characteristic value is varied, within the observation period, monotonously at a predetermined slope t > S) and an alarm is given. In the case of K3, the fire characteristic value Uk is within the hazard range (9 to 11) throughout the observation time period and an alarm is given.In the case of K4, as in K3, the fire characteristic value is continuously above the alarm level 11 throughout the observation time period and an alarm is given. The normal operation range of the fire alarm system is within 2 to 11.

This fire alarm system, however, has not a function more than the function to determine whether a fire has started or not and cannot preestimating, based on the detection results, a degree of danger which will threaten the people in no distant. By this reason, suitable action against a fire which is coped with the progress of the fire, e.g. guidance for escape, cannot always be taken.

It is an object of the present invention to provide a fire alarm system which is capable of enabling proper guidance for escape coped with the course of the fire progress and the degree of urgency by computing and preestimating a time necessary to reach the level which is dangerous to the people, based on the data of a change in the physical phenomena of the surroundings, comparing the time required to reach the dangerous level with a time required for escape and generating a fire alarm in relation with the time for escape.

It is another object of the present invention to provide a fire alarm system which is capable of eliminating a delay of the data processing by presetting a level for starting computation for determination of a fire, and starting such computation by calculating a degree of danger based on all the data from the beginning only when the detection data is as high as said level. As a result, the computation can be omitted within a range where the data is determined not to be a fire so as to make computation only within the range where the data is determined to be fire.

It is a further object of the present invention to provide a fire alarm system wherein a fire level is set as well as a dangerous level which is determined as dangerous to the people, so that it may generate an alarm when the degree of danger threatening the people on a fire spot, which is computed from the detected data, is below said dangerous level but it exceeds the fire level.

In accordance with the present invention, there is provided a fire alarm system which detects a change in the physical phenomena of the surroundings caused by the occurrence of a fire, in an analog form by a detector, and samples the detection data periodically by a central signal station to make determination of fire, which system is characterized in that it comprises an operation unit for computing and preestimating a time required to reach the level which is judged as dangerous to the people, based on the detection data sampled periodically; and a comparing means for comparing the computed and preestimated time required to reach said level with a time necessary for escape from a fire spot which decides the degree of danger exceeds an allowable level when the time for escape is shorter than the computed and preestimated time and generates an alarm.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 7A is a block diagram of the fundamental formation of a conventional fire alarm system, Figure 1B is a diagram showing determination criterion of a fire characteristic; Figure 2 is a diagram of the detection data detected by analog type fire detectors; Figure 3 is a block diagram of a first embodiment of the present invention; Figure 4 is a program flowchart of the embodiment shown in Figure 3; FigureS is a block diagram of a second embodiment of the present invention; Figure 6 is a diagram showing determination criterion for information; Figure 7 is a circuit block diagram of third embodiment of the present invention;; Figure 8 is a program flowchart of the difference value computing processing operation of the third embodiment; Figure 9 is a time chart showing changes in temperature and densities of smoke and CO gas; Figure 70 is a time chart showing an operating waveform of a logical determination section.

Afire alarm system of the present invention is so constructed that it converts changes in the physical phenomena of the surroundings into a multi-degree approximation equation based on analog detection data of temperature, densitites of smoke and CO gas detected by an analog fire detector and obtains a degree of danger by the approximation equation so as to generate a fire alarm when the degree of danger is above the preset level.

The term "degree of danger" is used here to means a time which is required for the surrounding condition to reach a certain dangerous condition to the people. For example, as to the temperature, a dangerous temperature TD is set for the surrounding condition which is dangerous to the people as shown in Figure 2, and the times R1, R2 and P3 required to reach the dangerous temperature T0 are defined as the degrees of danger in the fires A, B and C, respectively. Therefore, the smaller of the value of the degree of the danger, the larger the degree of danger to the people becomes.

A threshold level Rs which is a reference value for the determination of the degree of danger is defined as a time necessary for escape from the spot of fire which is determined considering the various conditions of the spot of fire.

There will now be described a first embodiment of the present invention.

Figure 3 is a block diagram of a fire alarm system of the first embodiment of the present invention. la, .... . , in each designates a fire detector which detects a fire in analog form in proportion to the changes in the physical phenomena of the surroundings caused by a fire. Each of the fire detector comprises a detector means 2 for detecting a temperature, densities of a gas or smoke, an A/D converter 4 for converting the analog value detected by the detector means 2 into a digital value and a transmission circuit 3 for transmitting the detected data. Numeral 10 designates a central signal station having a microcomputer and connected to the plural fire detectors 1 a, ..... in by signal lines. 11 is a receiving circuit for sequentially receiving, at certain time intervals, the A/D converted analog detection data from the respective fire detectors la, it. . . in while identifying them. The detection data received by the receiving circuit 11 are input to a storing circuit 12 and stored there with respective addresses. 13 is an approximate-equation converting circuit for converting the stored contents in the storing circuit 12 into an approximation equation. The approximate-equation converting circuit 13 is connected to a degree-of-danger computing circuit 14 where the stored contents is computed by the degree-of-danger circuit 14.The so obtained value of the degree of danger is compared with a predetermined alarm reference value to allow a fire determining circuit 15 to determine a fire and to generate an output to drive an alarming circuit 16 formed of an alarm lamp and buzzer.

Figure 4 is a program flowchart of the approximate-equation converting circuit 13, the degree-of-danger computing circuit 14 and the fire determining circuit 15. The operation of the fire alarm system of the present invention will now be described referring to the program flowchart.

The detection data from the fire detectors 1 a, it. . . in are sequentially received, at predetermined time intervals, by the receiving circuit 11 while being identified with respect to the fire detectors. Nowletm detection data from the fire detector I a be: (xi, f(x1)) Xp, f(x2) ). . .( xm, f(xm) where x1,x2.. . xm each represent a detection time and f(x1),f(x2)... f(xm) each represent an analog amount with the detection time. These detection data (x1, f(x1) ) ( x2, f(x2) ) . . . (urn, f(xm) ) are stored by the storing circuit 12 and input to a block g. Blocks h, i, and j show the process of conversion of them detection data into a quadratic approximation equation. The method of working out the simultaneous equations as shown in block based on the m detection data will be explained using the method of least squares. Now, letting data functions obtained from them detection data (x1,f(x1)) (x2,f(x2)). . . (xm,f(xm) ) bef(x),thequadratic approximation F(x) of the data function f(x) is expressed as follows: F(x) ax2 + bx + c (1) where a, b and care coefficients, respectively.

In order to obtain the approximation equation F(x) of the data function f(x), there may be obtained the coefficients a, band c of the F(x) which minimize the following formula (F(x) - f(x) )2 dx may be obtained. However, the actual data function f(x) is not a continuous one and obtained in the form of n discrete values and if function Q(a, b, c) of a, band c is expressed by

such a, b and c as make the Function Q(a, b, c) minimized may be obtained. Therefore,

The equations (3) is rewritten into

Since F(x) = ax2 + bx + c, the following simultaneous equations are obtained from (1) and (4).

In block h, each value of

of the left side of (5) is computed from the detection data of the block g and in block i, each value of the right side of the formula (5), i.e.

is computed from the detection data of the block g. In block j, the simultaneous equations (5) is calculated by the Guass -Jordan method from the left side of (5) computed in the block h and the right side of (5) computed in the block i to obtain the coefficients a, band c of the quadratic function F(x) = ax2 + bx + c which is the approximation equation of the data function f(x).

Blocks 1, u, v, and w show the process for calculating the degree of danger R based on the values a, b and c obtained in the block j. The method for computing the degree of danger R is as follows: Now letting the dangerous temperature which makes the surrounding dangerous to the people beT0, since the degree of danger R is a time required to reach the dangerous temperature TD, the degree of danger R is obtained by solving the following equation: F(x) = TD ..... (6) More specifically, the equation (6) is substituted for the equation (1), and there is obtained: ax2 + bx - (T0 - c) =0 (7) Since the degree of danger R is a value obtained from the equation (7) solved for x which is a time required to reach the dangerous temperature TD, it may be obtained as follows::

Therefore, by substituting the value of the dangerous temperature TD preliminarily set and the values of the coefficients a, b and c of the quadratic approximation equation F(x) obtained by the block j, for the equation (8), the value ofthe degree of danger R may be calculated.

The determination of the degree of danger R will now be explained.

After the values of the coefficients a, band c have been obtained by the calculations in the blocks h, i and j, the following formula b2 + 4a (TD - C ) (9) is calculated in the block 1 and the obtained value is subjected to the determination in the block u as to the following: b2+4a(TD-c) > O (10) It suffices to continue the calculation only when the value of the degree R of danger is a real number in (8), i.e. the value of (9) becomes a positive number. Therefore, if (9) is a negative number like the detection data of curve C in Figure 2, the block g is resumed again after the determination in the block u to extract the detection data of predetermined time period from the respective fire detectors 1 a, it .. . in.

Although the approximation equation computed based on the analog detection data from the analog fire detector is a quadratic function, an approximate equation of cubic or more degrees may be employed. In the latter case, more accurate degree of danger can be obtained.

The AID converting circuit may be incorporated into the central signal station instead of being provided in the respective fire detectors. In this case, the circuit arrangement of the fire detector can be simplified and rendered small-sized. An erasing circuit for erase the analog detection data of below a predetermined level may be provided in the signal station to allow the capacity of the storing circuit to be smaller.

The degree-of-danger computing circuit may alternatively be such that it obtains the degree of danger in the form of a difference value of difference in the detection data as will be described in detail later. The difference value is used herein to mean a value obtained by substituting the difference in the detection data for a difference equation.

A second embodiment of the present invention will now be described.

The second embodiment is so formed that it obtains difference of the detection data such as a temperature, a densities of CO gas, or smoke which are detected by the detectors in the form of a difference value, compares the difference value with a first threshold level and a second threshold level, to give an alarm when the difference value exceeds the second threshold, cancel the detection data below the first threshold level to reduce the burden of the computing processing operation of the central signal station, convert the detection data from the detector into an approximation equation when the difference value exceeds the first threshold level but is below the second threshold level, and obtains the degree of danger from the approximation equation to effect the fire determination.

Figure 5 is a block diagram of a fire alarm system according to the second embodiment of the present invention.

la, 1 b . . . 1 n are fire detectors for detecting, in analog form, a change in physical phenomenon of the surroundings caused by occurrence of a fire. Each of the detectors comprises a detecting means 2 for detecting a temperature, a density of a CO gas or smoke and a transmission circuit 3 for transmitting the detected data detected by the detecting means 2. 20 is a central signal station including a microcomputer therein for carrying out computing processing operation based on the detection data from the fire detectors 1 a, 1 b . . . in. The signal station 20 is connected to the plurality of detectors la, it .. . in by signal lines. 21 is a receiving circuit for sequentially receiving, at predetermined time intervals, the detection data while identifying them, and 22 is an A/D converting circuit for converting the analog value of the detection data received by the receiving circuit 21 into a digital value. The detection data after the AID conversion are input to a storing circuit 23 and stored there at addresses assigned to the respective detectors 1 a, 1 b . .. 1 n, respectively. 24 is an average value computing circuit which sequentially takes out the detection data for the respective detectors stored in the storing circuit 23 by groups of three and makes computation to obtain an average value of the taken-out three data values for preventing an error alarm from being generated by an abnormal data value produced by a noise. 25 is a difference value computing circuit for computing an amount of change for every predetermined period, taking the difference of the respective average values as a difference value. The difference value representing the change amount for every predetermined period is output to a difference value determinating circuit 26.In the difference value determining circuit 26, a second threshold level a and a first threshold level ss which is lower than the first threshold level cr. a are preliminarily set and they are compared with the difference value computed by the difference value computing circuit 25.

As a result of the comparison by the difference value determining circuit 26, if the difference value is below the first threshold value ss, determination of non-fire is made and the detection data is erased to reduce the burden of the computing processing operation in the signal station 20. If the difference value is above the second threshold level a, an alarming circuit 29 comprising a buzzer and an alarm lamp is driven to immediately make a fire alarm indication.When the difference value is above the first threshold level ss but below the second threshold level, the relevant detection data stored in the storing circuit 23 is taken out and output to an approximation equation computing circuit 27 to effect conversion into an approximation equation. 28 is a degree-of-danger determining circuit which computes the degree of danger R based on the converted approximation equation and compares it with a preset threshold level Rs. When the degree of danger R is smaller than the threshold level Rs, i.e. the degree of danger is higher than the preset degree of danger represented by the threshold value Rs, the alarming circuit 29 is driven to generate a fire alarm.

In the foregoing, the first threshold level ss and the second threshold value a represent a difference value which is expected to reach an alarm level and a fire level of Figure 6, respectively within a predetermined time period. The degree of danger R is a time required to reach the dangerous level and the threshold level Rs is a time necessary to escape from the fire spot.

In accordance with the second embodiment, a difference value is computed based on the detection data sampled for predetermined period and a fire alarm is given upon comparison with the second threshold value preliminarily set so that a fire which shows linear and abrupt change in physical phenomenon can be detected in its early stage.

Further according to the present embodiment, the detection data whose difference value is below the first threshold level is cancelled and the detection data whose difference value is above the first threshold level but below the second threshold level is converted into the approximation equation based on the detection data from the detecting means to obtain the degree of danger from the approximation equation and given an alarm in relation with the threshold level preliminarily set. Thus, the burden of the computing processing operation by the signal station is reduced and necessary detection data can be processed more rapidly and the reliability of the fire alarm system can be increased through accurate fire determination.

Still further according to the present embodiment, when the detection data exceeds the second threshold level, i.e., the fire level, a fire alarm is immediately generated irrespective of the succeeding estimation and computation. Therefore, even when the degree of danger is not high enough to generate an alarm, it can be possible to inform a dangerous condition. Thus, the fire alarm system can improve security against a fire.

In the second embodiment, for the computation of the difference value of the respective average values which is computed based on the groups of plural detection data, e.g. three detection data, of the predetermined period, detection data may be partly overlapped with detection data of the succeeding or preceding group so as to be subjected to the computation for the fire determination. Thus, the computation of the difference values can be made from a reduced number of detection data and a fire determination can be made more rapidly.

In addition to the alarm level, another preset level may be provided so as to preliminarily initiate computation when the detection data is below the alarm level but exceeds this preset level. In this case, immediately the detection data exceeds the preset level, the computation of the approximation equation is started to eliminate a delay in processing time. The computation starting level in the present embodiment corresponds to an alarm level or a preset level, if it is provided.

Although the threshold level Rs, i.e. a time required for escape may be selected suitably, considering various conditions of the place where the fire detector is installed, a time Rp necessary for preparation for escape may be further set in addition to the threshold level Rs. With this arrangement, when the degree of danger R is determined to be within the preparation time Rp after the preestimation and computation thereof, an attentioning signal may be generated.

There will now be described a third embodiment of the present invention.

The third embodiment is so formed that detection data of plural physical phenomena which are caused to change by occurrence of a fire are preestimated, computed and determined, and as a result thereof, only when the degrees of dangers with respect to two or more physical phenomena are larger than the threshold level, determination of fire is made. In this embodiment, a time required to reach a dangerous level is computed from the detection data and when the computed time is within a set time necessary for escape, a danger signal is transmitted and when the computed time is below the set time, an uncertainty signal is transmitted.Logical determination is made based upon the danger signal and uncertainty signal, in such a manner that when the danger signal is obtained, a fire signal is output and when the uncertainty signal is obtained after the danger signal has been gotten already, a fire signal is transmitted, and even when the danger signal disappears, a fire signal is continued to be output for some time period.

Figure 7 is a circuit block diagram of the fire alarm system according to the third embodiment of the present invention and Figure 8 is a program flowchart showing the operation ofthethird embodiment.

The third embodiment will now be described in detail referring to Figures 7 and 8. 31 is a temperature sensor for detecting, in an analog form, an ambient temperature which is caused to rise by a fire, 32 is a gas sensor for detecting a density of CO gas generated by a fire, and 33 is a smoke sensor for detecting a density of smoke which is caused by a fire. A temperature detection signal T, a gas density signal G and a smoke density signal S are output in the form of analog detection signals from the temperature sensor 31, the gas sensor 32 and the smoke sensor S, respectively.

34 is a difference value computing and determining section which samples, at predetermined time intervals, the analog detection signals from the temperature sensor 31, gas sensor 32 and smoke sensor 33, respectively carries out the computation of difference values each time several number of, for example m, sampled data are obtained so as to calculate a time required to reach a threshold level which is dangerous to the people and makes determination of danger, uncertainty or safety.

The determination of a fire by the preestimation and computation based on the detection data, which is carried out at the difference value computing and determining section 34, is made according the computation routine shown by in flowchart of Figure 8 wherein the temperature data T is exemplarily shown.

First, at block a, an average value Ta is computed upon every sampling of m temperature data according the following formula:

After the computation at the block a, a difference value (Ta - (Ta - 1) ) is calculated at block b based on the average value Ta - 1 previously obtained in the preceding cycle. Thereafter, at block c, a slope a of the temperature change is calculated by dividing the difference value (Ta - (Ta - 1)) by a sampling time to (a fixed value).Then, at block d, a time t which is required to reach a predetermined threshold level TD for a dangerous temperature which is determined as a fire according to the following formulae: T0 = at + Ta t = ( - Ta )/(y Succeedingly, at determinating block e, a first threshold level, i.e., time tl and the time t computed at the block d are compared with each other and when the time t is below the first threshold level, time to, the determination is made to be a fire and a danger signal is output at block f.

In this connection, it is to be noted that the first threshold level, time tl, is a time for determining danger or uncertainty and it corresponds to the time Rs for escape or the preparation time Rp in the foregoing embodiments. The time t corresponds to the time R required to reach the dangerous level in the second embodiment. However, the threshold level TD of dangerous temperature may differ from a dangerous level and it may be a fire level. In the latter case, the first threshold time tl may be changed.

On the other hand, if the time t is larger than the first threshold time tl at the determining block e, the time t required to reach the dangerous temperature TD is compared with a second threshold time t2 to determine at the block g as to whether the time t is safe and free from a fire or uncertain or doubtful. When the time t is below the second threshold time t2, an uncertainty signal is output at block h. When the uncertainty signal is output at block i, the operation proceeds to a function approximation computation routine. When the time tl is above the second threshold time t3 at the determining block g, the temperature rise is determined to be due to other cause than a fire and determined to be safe at the block i.

After completion of the series of determination operation based on the difference values, the previous average value Ta-l is substituted for the average value Ta now obtained at the blockj and the operation is returned to the block a.

Referring again to Figure 7, a function approximation computing and determining section 35 is provided after the difference value computing and determining section 34 so that the function approximation computing and determining section 35 may carry out the computation and determination of fire based on the detection data from the respective detector sensor in such a manner as in the first embodiment only when the difference value computing and determining section 34 outputs an uncertainty signal.

A danger signal output after the operation by the difference value computing and determining section 34 and the function approximation computing and determining section 35 is input to a logical determining circuit 36. The logical determining circuit 36 carries out logical determination in such a manner that when danger signals based on at least two different detection data are generated, a fire signal is output.

More specifically, letting a danger signal based on the temperature data, a danger signal based on the gas density and danger signal based on the smoke density output from the difference value computing and determining section 34 be dl, d2 and k3, respectively, and letting a danger signal based on the temperature, a danger signal based on the gas density and a danger signal based on the smoke density which are output from the function approximation computing and determining section 35 be d10, d20 and d30, respectively, logical sums of the danger signals dl and d10 based on the same detection data, of the danger signals d2 and d20 based on the same detection data and of the danger signals d3 and d30 based on the same detection data are taken out through OR gates 37,38 and 39, respectively.As a result, a temperature danger signal Et is output from the OR gate 37, a gas danger signal Eg is output from the OR gate 38 and a smoke danger signal Es is output from the OR gate 39. The outputs from the OR gates 37 to 39 are input to AND gates 40, 41 and 42. The AND gate 40 outputs a H-level signal i.e. signal Etg when the temperature danger signal Et and the gas danger signal Eg are obtained. The AND gate 41 outputs a H-level signal i.e. signal Egs when the gas danger signal Eg and the smoke danger signal Es are obtained. The AND gate 42 generates a H-level signal i.e. signal Ets when the smoke danger signal Es and the temperature danger signal Et are obtained.

The outputs from the AND gates 40 to 42 are all input to an OR gate 43 to be output as a H-level signal of the OR gate 43 so as to generate a fire signal through an OR gate 44.

In addition to the logical determining circuit 36, which determines a fire and outputs a fire signal based on at least two danger signals, a logical determining section 55 is provided to continue output of a fire signal when an uncertainty signal is obtained after the fire signal has been output based on the danger signals or when neither of danger signal and uncertainty signal are obtained temporarily.

The logical determining section 55 comprises an OR gate 45 to which uncertainty signals ul, u2 and u3 corresponding to the respective detection data from the difference value computing and determining section 34 are input and an OR gate 46 to which uncertainty signals u10, u20 and u30 from the function approximate computing and determining section 35 are input. Outputs from the OR gates 45 and 46 are supplied directly to one of the inputs of OR gates 49 and 50, respectively and further supplied to another input through delay circuits 47 and 48, respectively. Outputs from the OR gates 49 and 50 are connected to one of inputs of AND gates 51 and 52, respectively. Other inputs of the respective AND gates 51 and 52 are so connected as to receive an output of the OR gate 44 through a delay circuit 54. Outputs from the AND gates 51 and 52 are input to OR gate 53 and an output from the OR gate 53 is supplied to one of the inputs of the OR gate 44 whose other input is so connected as to receive the output from the logical determining circuit 36.

The delay circuits 47, 48 and 54 each have a function to delay the signals input thereto by one cycle of computation by the difference value computing and determining section 34 and the function computing and determining section 35.

In this connection it is to be noted that the logical determining circuit 36 may also output a fire signal in response to a combination of two or more different kinds of danger signals from the difference value computing and determining section 34 and the function approximation computing and determining section 35.

The operation of the logical determining section 55 in the embodiment of Figure 7 will now be described.

In the diagram of Figure 9, now assuming that the density of smoke or CO gas is increased with time due to smoldering and the smoldering is developed into a fire at a time tn, the density of smoke or CO gas is transiently reduced due to generation of hot air stream or complete combustion caused by the starting of fire. On the other hand, the temperature is kept substantially constant at the stage of smoldering before starting of fire as shown by a broken line, but it quickly rises after starting of fire at the time.

With respect to the change in the densities of smoke and CO gas and the temperature as shown in Figure 9, if danger signals d2 and d3 are output as a result of the computation and preestimation by difference value or function approximation based on the increase in the smoke density as shown for example by the time chart of Figure 10, the logical determining circuit 36 outputs a fire signal through the OR gate 44 by the two danger signals d2 and d3. Such danger signals d2 and d3 are transmitted every cycle of computation and preestimation which corresponds to a clock.

Thereafter, the densities of smoke and CO gas are lowered due to starting of fire at time tn and uncertainty signals u2 and u3 are began to be transmitted instead. In response to the uncertainty signals u2 and u3, the OR gate 45 of the logical determining section 55 generates a H-level output which is supplied to one input of the AND gate 51. At this time, a delayed output based on the danger signal of the previous period is being supplied to the AND gate 51 from the delay circuit 54, and the AND gate 51 is in its enable state. Therefore, a fire signal based on the uncertainty signals u2 and u3 are transmitted through the AND gate 51, OR gate 53 and the OR gate 44.

Subsequently, if the difference value computing and determining section 34 determines safety based on the lowering of the smoke and CO gas densities and no danger signal and uncertainty signal are generated, since the output of the OR gate 45 based on the previous uncertainty signal is being supplied to the OR gate 49 after being delayed by one cycle by the delay circuit 47 and at this time a delayed output is generated from the delay circuit 54 by the output of the previous fire signal based on the uncertainty signal, the AND gate 51 is in its enable condition and a H-level output based on the uncertainty signal delayed by the delay circuit 47 is transmitted as a fire signal through the OR gate 49, AND gate 51 OR gate 53 and OR gate 44.

Then, a certain length of time has been passed from the starting of fire, the densities of smoke and CO gas begin to increase again. Therefore, uncertainty signals u2 and u3 are transmitted again and they are switched to the danger signals d2 and d3, so that a fire signal is continued to be output from the OR gate 44 irrespective of the transient condition which is determined to be safe.

Although the logical determination is carried out based on the danger signal obtained by the combination of the difference value method and the function approximation method in the third embodiment, determination of fire may be made in such a manner that a fire is determined when at least two danger signals are obtained from different kinds of detection data obtained by the fire determination according to the difference value method or function approximation method.

Various techniques disclosed in relation with the respective embodiments may be applied to any other embodiment as described above although the description thereof is omitted in the specification.

As described above, according to the present invention, a time required to reach the level which is dangerous to the people is computed and preestimated based on the data of a change in the physical phenomena of the surroundings and the time is compared with a time necessary for escape so as to give a fire alarm related to the escape time. Thus, suitable guidance for escape can be conducted.

Claims

1. A fire alarm system including a fire detecting means for detecting a change or changes in physical phenomena of the surroundings caused by a fire and a central signal station for periodically sampling the detection data from the said fire detecting means so as to make determination of fire, which system is characterized by a degree-of-danger computing circuit for computing and preestimating, based on said detection data sampled periodically, a time required to reach a level at which the physical change or changes in the surroundings is or are judged as being dangerous to the people; and a determining circuit for comparing said time with a preset time for escape from the fire spot so as to output a fire alarm signal when the former time is shorter than the latter time.

2. A fire alarm system as claimed in claim 1, wherein said computing circuit converts the detection data into an approximation equation and carries out the computation and preestimation by the functional approximation method.

3. A fire alarm system as claimed in claim 1, wherein said computing circuit carries out the computation and preestimation based on a difference value obtained from a difference between the detection data now sampled and the detection data sampled previously.

4. A fire alarm system as claimed in claim 1, wherein said computing circuit which compares a difference value obtained by first computation by the difference value method with a first and a second threshold level, outputs a cancelling signal for cancelling the detection data when the obtained difference value is lower than the first threshold level, outputs a fire alarm signal when the difference value is above the second threshold level, and carries out a second computation, by the functional approximation method, when the difference value is higher than the first threshold level but lower than the second threshold level.

5. A fire alarm system as claimed in claim 1,2,3 or 4, which further comprises a logical determining circuit for computing and preestimating, and determining the detection data of plural kinds of physical phenomena which are caused to change by a fire so as to output a fire alarm signal when the times required to reach the dangerous levels with respect to two or more physical phenomena, respectively are shorter than the preset time for escape.

6. A fire alarm system as claimed in claim 1,2,3,4 or 5, wherein said computing circuit is adapted to compare the periodically sampled detection data with a computation-initiating level so as to initiate the computation and preestimation only when said detection data exceed said computation-initiating level.

7. A fire alarm system as claimed in claim 1, 2, 3, 4, 5 or 6, wherein said determining circuit sets a fire level judged as being a fire in addition to the danger level which is judged as being dangerous to the people and outputs a fire alarm signal, irrespective of the computation and preestimation, when the detection data exceed said fire level.

8. A fire alarm system substantially as hereinbefore described, with reference to, and as shown in, Figures 2 to 10 of the accompanying drawings.