- Email: [email protected]
An automatic fire searching and suppression system for large spaces
ARTICLE IN PRESS
Fire Safety Journal 39 (2004) 297–307
An automatic fire searching and suppression system for large spaces Tao Chen, Hongyong Yuan*, Guofeng Su, Weicheng Fan State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230027, PR China Received 25 November 2002; received in revised form 11 August 2003; accepted 19 November 2003
Abstract An automatic fire searching and suppression system with remote-controlled fire monitors for large spaces is developed. The fire searching method is realized based on computer vision theory via one CCD camera fixed at the end of a fire monitor chamber. While the fire monitor is pivoting, continuous images are taken from the CCD camera and transmitted into a computer. Then the images are processed with an image fire detection method to determine whether a fire occurs in the vision field. Once a fire is detected, it will be automatically located through an image processing algorithm. Displacement and pivot angle of the CCD camera in searching process are the essential parameters to calculate the space coordinates of a fire. When the coordinates of the fire are obtained, the fire monitor can be adjusted to the appropriate direction and elevation to spray according to water pressure. r 2003 Elsevier Ltd. All rights reserved. Keywords: Automatic fire monitor; Fire searching; Fire suppression; Large spaces
1. Introduction Water is most acceptable for fire suppression in large space when performance and quantity are taken into account. In this case, water type fire suppression apparatus have many advantages such as larger protection area and low suppression cost. Furthermore, it does not produce toxic products. Sprinklers, as the most common suppression apparatus, have been widely installed for fire protection. However in
*Corresponding author. Fax: +86-551-3606430. E-mail address: [email protected] (H. Yuan). 0379-7112/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.firesaf.2003.11.007
ARTICLE IN PRESS 298
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
Nomenclature D chamber length of the fire monitor d measured distance between a fire and the pivot point of the fire monitor dc calculated distance between a fire and the pivot point of the fire monitor f focal length of the CCD camera e distance between a fire and the shooting spot of the fire monitor (i1, j1) pixel coordinates of a fire in the image at time t1 (i2, j2) pixel coordinates of a fire in the image at time t2 H maximum pixel number per row of the CCD h actual width of the CCD T time of extinguish after the water is issued Ts time of searching process V maximum pixel number per column of the CCD v actual height of the CCD X–Y–Z fixed object space coordinate system X1–Y1–Z1 camera coordinate system at time t1 X2–Y2–Z2 camera coordinate system at time t2 (X,Y,Z) coordinates in X-Y-Z coordinate system (X1,Y1,Z1) coordinates in X1-Y1-Z1 coordinate system (X2,Y2,Z2) coordinates in X2-Y2-Z2 coordinate system x–y image plane of the camera (x,y) coordinates in x–y image plane (x1,y1) coordinates in image plane at time t1 (x2,y2) coordinates in image plane at time t2 a angle to Z-axis in Y–Z plane of the fire spot b visual angle of the CCD camera o1 angle to Z-axis in Y–Z plane of Z1-axis o2 angle to Z-axis in Y–Z plane of Z2-axis recent years, with the increasing large space buildings, the suitability of sprinkler use in such large space situations has been challenged. Commonly, thermally activated sprinklers are not suitable for high ceiling space use. The height of the ceiling in large space will greatly affect the sprinklers so that they cannot provide effective protection. The main problem is the activation delays of the sprinklers in large spaces, particularly high ceiling spaces. For example, even a 5 MW fire on the atrium floor would not generate a smoke temperature high enough to activate the sprinklers on an atrium ceiling higher than 15 m [1, 2]. Due to the distance between the potential fire source and the sprinkler heads which are mounted near the ceiling, sprinkler activation may be too late to minimize the fire hazards or damage. Even the early suppression fast response (ESFR) sprinklers have the recommended height limit [3–5]. Moreover, the height may also affect how much water can reach the flame before vaporized or blown away by the fire plume [6]. In those large spaces where the combustible materials are distributed
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
299
dispersedly, it is also not very efficient to install many sprinklers to cover all these materials. Now, robotic fire monitor that can be automatically controlled by computer and can work as a linkage device in a fire detection and suppression system is becoming a more suitable solution. Liu et al. [7] and Yuan et al. [8] have done some early researches. Compared to a sprinkler, a fire monitor has many advantages. First, the most remarkable advantage is that the activation time of these fire monitors is much shorter than sprinklers. They are activated by the alarm signal given by the fire detectors which are much more sensitive than the sprinklers’ explosion glass bulbs. These detectors can be conventional fire detectors or gas sensors. Second, water stream from a fire monitor has a higher speed, a greater flux and a larger impulse so it is more effective for fire suppression. Its spot type suppression may sometimes avoid the consequent losses caused by sprinklers and will not cause a downward moving of smoke [9] to endanger the occupants in the building. Last, a typical fire monitor has a shooting range of 50 m long, which enables it to protect much larger area than a sprinkler. In this paper, a new fire searching and suppression system using such automatic fire monitors is described. These fire monitors are assembled into a larger fire detection–suppression system. After fire confirmation and searching process, the direction and elevation of the fire monitor can be easily calculated and suppression can consequently be executed.
2. Principle 2.1. Structure of the automatic fire monitor system The automatic fire monitor system is a fire detection–searching–suppression system [10] which consists of three parts: the fire detection module (including detectors and the detector controller), the fire monitor module (including the fire monitor, the fire monitor manual controller and the CCD camera) and the central control module (including the computer, data-sampling interfaces and communication interfaces). In this system (shown in Fig. 1), the fire monitor serves as a fire searching and suppression device in conjunction with the fire detectors. Once the detector is in alarm state, the fire detection module will give a fire alarm signal and the central control module will send a linkage signal to activate the corresponding fire monitor. The fire monitor module and the central control module accomplish the fire searching and suppression after the fire monitor is activated. An automatic fire monitor itself is much like a little barbette which consists of a chamber, a CCD camera, a motor, an electromagnet valve, a computer connection interface (RS485 and video) and a shell. At the end of the fire monitor chamber, a CCD camera is fixed which is used for capturing the spot images. The optical axis of the CCD camera is adjusted parallel to the axis of the fire monitor chamber. In large space condition, the two axes can be practically considered coincident. The electromagnet
ARTICLE IN PRESS 300
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
Fig. 1. Sketch of automatic fire monitor system.
Table 1 Technical specification of the water cannon Maximum operating pressure Operating pressure Flow rate Pivot range Pivoting speed Remote control Computer interface
16 bar (16 105 Pa) 8 bar (8 105 Pa) (lower pressure is allowable) 1200 lpm 80 ?+60 max vertical, 7100 max horizontal 9 /s RS-485 bus RS-232 (with a protocol conversion box)
valve and the motor inside the fire monitor shell are controlled by the computer via RS-485 serial communication interface. The former releases or holds the water jet and the latter drives the fire monitor chamber to pivot in left–right and up–down directions. Furthermore, the pivot angle of the chamber is fed back to the computer as an important parameter to the fire searching algorithm. The fire monitor has dual control modes. A manual fire monitor controller is used for manual operations at emergency situation. In case a fire is discovered by a human, the cannon can be operated manually by a trained personnel. In the automatic mode, multiple fire monitors can be controlled and switches between them are available. The main technical specifications of a typical fire monitor are shown in Table 1. 2.2. Fire searching method based on computer vision theory Computer vision tries to simulate man’s vision and reconstruct 3D scene with 2D images. Usually, at least two cameras are needed to construct a 3D vision system [11]. Baseline distance between the two cameras is essential to reconstruct 3D coordinates. The relationship between image coordinates and object coordinates
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
based on single fixed camera imaging system can be established as Xo xi ¼ f ; Zo Yo yi ¼ f ; Zo
301
ð1Þ
where (xi, yi) represent the image coordinates, (Xo, Yo, Zo) represent the object coordinates and f represents the camera’s focal length. Here we use only one CCD camera to construct a vision system according to the position change of the camera between time t1 and t2 when it is pivoting in Y–Z plane. Fig. 2 shows the coordinates system in our vision system. *
*
* *
*
The pivoting point of the camera–fire monitor system is the origin of X–Y–Z coordinate system. The camera’s optical center is the origin of the X1–Y1–Z1 and X2–Y2–Z2 coordinate systems. X–Y–Z, X1–Y1–Z1 and X2–Y2–Z2 are right-handed coordinate systems. In X–Y–Z coordinate system, o measures zero along Z-axis and positive by righthand rule with X-axis as the thumb direction. Thus we have o1o0 and o2>0. P(d,a) in the Y–Z plane is supposed to be the fire position in object space. From Eq. (1) we have Y1 Z1 ¼ f ; y1 Y2 Z2 ¼ f : y2
ð2Þ
Between object space coordinates and image space coordinates we have Y ¼ Y1 cos o1 Z1 sin o1 þ D sin o1 ; Z ¼ Y1 sin o1 þ Z1 cos o1 þ D cos o1 ;
Fig. 2. Coordinates built from computer vision theory.
ð3Þ
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
302
Y ¼ Y2 cos o2 Z2 sin o2 þ D sin o2 ; Z ¼ Y2 sin o2 þ Z2 cos o2 þ D cos o2 :
ð4Þ
Take Eq. (2) into (3) and eliminate Y1, the relationship between Y and Z has an expression ðy1 cos o1 f sin o1 ÞðZ D cos o1 Þ þ D sin o1 : ð5Þ Y¼ y1 sin o1 þ f cos o1 Take Eq. (2) into (4) and eliminate Y2, the relation between Y and Z has another expression ðy2 sin o2 þ f cos o2 ÞðY D sin o2 Þ þ D cos o2 : ð6Þ Z¼ y2 cos o2 f sin o2 Solution of Y and Z can be obtained from Eqs. (5) and (6), as shown in Eq. (7). Y¼
Dðy2 f tan o2 Þ½ðsin o2 sin o1 þ A cos o1 B cos o2 Þ=ðA þ BÞ D cos o2 y2 tan o2 þ f
þ D sin o2 ; Z¼
D ðsin o2 sin o1 þ A cos o1 B cos o2 Þ; AB
ð7Þ
where A ¼ ðy1 f tan o1 Þ=ðy1 tan o1 þ f Þ; B ¼ ðy2 f tan o2 Þ=ðy2 tan o2 þ f Þ:
ð8Þ
In the above equations, y1 and y2 are still unknown. Actually, they can be calculated from the pixel coordinates (i, j) of the images, because most of the CCD camera are of the same standard specifications. Suppose the CCD camera’s scanning area is known as H V pixels and h v m2, the relationship between [y1, y2] and [j1, j2] can be found. y1 ¼ ðj1 V =2Þv=V ; y2 ¼ ðj2 V =2Þv=V : Thus the fire position P(d,a) in the space is confirmed and expressed as pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d ¼ Z2 þ Y 2 ; a ¼ tan1 ðY =ZÞ:
ð9Þ
ð10Þ ð11Þ
2.3. Working process Initially, the fire monitor is set at the horizontal-left limit position. Once a fire is detected by a fire detector in the system, the corresponding fire monitor will be activated. It will start searching for fire and be driven to the down-right limit position step-by-step (shown in Fig. 3). The fire monitor rests for a short time after each step. During this period of time, continuous images are captured from the CCD
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
303
Fig. 3. Fire monitor’s scanning process. 1: horizontal-left limit; 6: down-right limit.
I
II
t1 fire monitor pivot
fire monitor pivot
y x IV
III
t2
fire monitor pivot
Fig. 4. Aiming process when a fire is detected.
camera and sent into computer to be processed by image fire detection algorithm [12]. In the searching process, the robotic fire monitor scans in horizontal direction for three times however, each time in a different vertical angle. If no fire is detected in the entire searching process when the fire monitor reaches its down-right limit, it will be reset to its initial position. Otherwise, the locating algorithm is employed. In the locating algorithm, the distance between the fire monitor and fire is calculated. The step angle of the fire monitor is chosen as b (less step angle can be chosen) which is the visual angle of the CCD camera, thus no protection area is skipped. By pivoting the fire monitor, we perform the calculation by the displacement at different time. Images I, II, III and IV in Fig. 4 show the searching and aiming movements.
ARTICLE IN PRESS 304 *
*
*
*
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
First, when a fire region is detected on the image, mark the region and its gravity center. Move the fire monitor and mark the fire region repeatedly until the fire region reach the bottom edge and x-center of the image. Second, the vertical pivot angle of the fire monitor at this time (t1) is recorded as o1. Move the fire monitor vertically until the fire region reach the top edge of the image. Third, the vertical pivot angle at this time (t2) is recorded as o2. Move the fire monitor vertically until the fire region is at the center of the image. Thus combined with step two, the coordinate systems as shown in Fig. 2 are formed. Last, now the fire monitor nozzle is pointed right to the fire, record the vertical pivot angle as o3.
Now the distance d between the fire and the fire monitor can be calculated from computer vision theory with the aforesaid coordinate systems. Longer baseline yields more accuracy in fire location, so in image II and image III, the fire region is moved from one edge to another so that |o2o1| is as large as possible to achieve long baseline. 2.4. Suppression characteristic Above describes the fire searching process. To shoot the fire with water stream, change the elevation of the chamber according to d, a, o3 and water pressure. After the water pump is started up, the fire monitor can spray once the electromagnet valve is opened. While spraying, the chamber will swing in about 75 in all directions to fully cover the fire region. The diameter of water stream can be adjusted according to distance and environment in order to achieve best suppression effect. The maximum detection distance of the CCD is 100 m and the maximum spray distance of the fire monitor is 50 m. The protection area is considerable for the application in large space. By proper installation of multiple fire monitors, the protection area can be almost fully covered. Fig. 5 shows the protection area. The vertical limit of the fire monitor is 80 , so there will be a dead area right below each fire monitor. Usually the dead area can be ignored because it is relatively small. For example, a fire monitor mounted at 8 m only has a dead area of about 3.1 m2.
Fig. 5. Protection area of the fire monitors.
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
305
3. Experiment Experiments were conducted in a large test hall which is 30 m high, 30 m long and 18 m wide. The fire monitor was installed on one wall at the height of 6 m. Fuels in different tests were placed in a line on the ground of the hall every 2 m from the fire monitor (recorded as L). In each test, the fire monitor started its search from the horizontal-left limit. Water pressure is 4 bar. Different fuels, such as diesel oil, wood, and paper box are tested separately. Fig. 6 shows the experimental setup. Usually, the spraying lasts for 10 s and during this time the chamber will swing in 75 in all directions for 3 times. Table 2 shows the data for diesel oil fire tests. The fire is a 0.2 m 0.2 m pool fire ignited by flock. In all tests, the values of e are obtained by eyeballing and are of low precision. Searching time Ts varied in different tests, but usually it was less than 30 s if a fire is found. In the test data of the same fire type, all the former three Ts values were obviously greater than the later three Ts values. This was caused by the limitation of the CCD camera’s vision field since the fire monitor started its search from the same point in our tests. Fires farther than 16 m were detected in 1–2 scanning period (reference to Fig. 3) and fires between 10 and 16 m were detected in 3–4 scanning period (reference to Fig. 3) after the fire monitor chamber pivoted down. Generally,
Fig. 6. Experimental setup.
Table 2 Experimental data (diesel oil) Number
Fire type
L (m)
d=(h2w+L2)0.5 (m)
dc (m)
Ts (s)
e (m)
T (s)
1 2 3 4 5 6
Diesel Diesel Diesel Diesel Diesel Diesel
10.0 12.0 14.0 16.0 18.0 20.0
11.66 13.42 15.23 17.09 18.97 20.88
11.86 13.14 15.07 17.26 18.93 20.30
25.3 22.2 23.8 14.9 12.2 12.3
0.3 0.1 0.2 0.1 0.0 0.1
5.1 3.2 4.0 3.7 2.9 4.2
oil oil oil oil oil oil
ARTICLE IN PRESS 306
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
searching time varied with fire position, fire strength and computation depth of our detection algorithm, which will not be further discussed here. Calculated distance and the actual distance are fairly accordant. The deviation is mainly due to the low precision of the pivot angle fed back to the computer. The angle measuring device in the fire monitor is quite simple and the motor gears also have mechanical errors. Extinguishing time T is usually smaller than 6 s because the fire strength in our tests is very small while the water flux is relatively large. Generally, larger e caused longer extinguishing time. Usually, if the water stream dose not hit the fire spot initially, it will cover the fire spot while the fire monitor is swinging.
4. Conclusion Fire searching and suppression were combined together and realized automatically in the automatic fire monitor system. Displacement and pivot angle of the CCD camera in fire searching process are the essential parameters to calculate the space coordinates of fire. Once the direction and the distance of the fire are obtained, the horizontal pivot angle and the vertical elevation of the fire monitor can be calculated according to water pressure. The fire searching precision is enough for practical use and the suppression effect is also satisfactory. Remote and automatic control of the fire monitor improves its efficiency and adaptability. Moreover, it provides more safety in fire fighting and is very economical when incorporated with fire protection system for large spaces use. Instead of installing multiple layers of sprinklers, the application of the fire monitor will not influence the inside sight of the buildings. It can be very useful to apply this technology in large spaces such as large museums, palaestras, showplaces and storehouses.
References [1] Chow WK. Performance of sprinkler in atria. J Fire Sci 1996;14(6):466–88. [2] Gott JE, Natariani KA. Analysis of high bay hangar facilities for detector sensitivity and placement. Society of fire protection engineers. Honors Lecture Series, May 20, 1996, Proceedings. Engineering seminars: Fire Protection Design for High Challenge of Special Hazard Applications, May 21–22, 1996, Boston, MA, 1996. [3] Hankins J. ESFR sprinklers–the facts you should know. Fire Prevention and Fire Safety Eng J 1995; 2(6). [4] Kung HC, et al. Early suppression fast response (ESFR) sprinkler protection for 12 m high warehouses. Proceedings of the Fifth International Symposium on Fire Safety Science. Melbourne, 1997. [5] Yao C. Overview of sprinkler technology research. Proceedings of the Fifth International Symposium on Fire Safety Science. Melbourne, 1997. [6] Chow WK. Full-scale burning facilities for atrium fire research. Fire Safety Sci 1993;2(2):61–4 [in Chinese].
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
307
[7] Liu Shenyou, et al. Automatic orientating fire extinguishing monitor. China Safety Sci J 2001; 11(2):37–41 [in Chinese]. [8] Yuan Hongyong, Chen Tao, Su Guofeng, Liu Binghai. Fire location and suppression with automatic hydrant in large space. Second NRIFD Symposium—Science, Technology and Standards for Fire Suppression Systems, Proceedings. Tokyo, Japan: 17th–19th July, 2002. [9] Cooper LY. The interaction of an isolated sprinkler spray and a two-layer compartment fire environment. Phenomena and model simulations. Fire Safety J 1995;26(1):1–33. [10] Fan Weicheng, Yuan Hongyong, Liu Shenyou. The integrated system for fire detection and extinction. Fire Safety Sci 1995;4(3):49–53 [in Chinese]. [11] Gao Wen, Chen Xilin. Computer vision—algorithm and principle. Tsinghua University Press: Beijing; 1999. [12] Yuan Hongyong, et al. Image type intelligent fire detection and location method. Safety Eng 1996; (3):17–19 [in Chinese].
Fire Safety Journal 39 (2004) 297–307
An automatic fire searching and suppression system for large spaces Tao Chen, Hongyong Yuan*, Guofeng Su, Weicheng Fan State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230027, PR China Received 25 November 2002; received in revised form 11 August 2003; accepted 19 November 2003
Abstract An automatic fire searching and suppression system with remote-controlled fire monitors for large spaces is developed. The fire searching method is realized based on computer vision theory via one CCD camera fixed at the end of a fire monitor chamber. While the fire monitor is pivoting, continuous images are taken from the CCD camera and transmitted into a computer. Then the images are processed with an image fire detection method to determine whether a fire occurs in the vision field. Once a fire is detected, it will be automatically located through an image processing algorithm. Displacement and pivot angle of the CCD camera in searching process are the essential parameters to calculate the space coordinates of a fire. When the coordinates of the fire are obtained, the fire monitor can be adjusted to the appropriate direction and elevation to spray according to water pressure. r 2003 Elsevier Ltd. All rights reserved. Keywords: Automatic fire monitor; Fire searching; Fire suppression; Large spaces
1. Introduction Water is most acceptable for fire suppression in large space when performance and quantity are taken into account. In this case, water type fire suppression apparatus have many advantages such as larger protection area and low suppression cost. Furthermore, it does not produce toxic products. Sprinklers, as the most common suppression apparatus, have been widely installed for fire protection. However in
*Corresponding author. Fax: +86-551-3606430. E-mail address: [email protected] (H. Yuan). 0379-7112/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.firesaf.2003.11.007
ARTICLE IN PRESS 298
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
Nomenclature D chamber length of the fire monitor d measured distance between a fire and the pivot point of the fire monitor dc calculated distance between a fire and the pivot point of the fire monitor f focal length of the CCD camera e distance between a fire and the shooting spot of the fire monitor (i1, j1) pixel coordinates of a fire in the image at time t1 (i2, j2) pixel coordinates of a fire in the image at time t2 H maximum pixel number per row of the CCD h actual width of the CCD T time of extinguish after the water is issued Ts time of searching process V maximum pixel number per column of the CCD v actual height of the CCD X–Y–Z fixed object space coordinate system X1–Y1–Z1 camera coordinate system at time t1 X2–Y2–Z2 camera coordinate system at time t2 (X,Y,Z) coordinates in X-Y-Z coordinate system (X1,Y1,Z1) coordinates in X1-Y1-Z1 coordinate system (X2,Y2,Z2) coordinates in X2-Y2-Z2 coordinate system x–y image plane of the camera (x,y) coordinates in x–y image plane (x1,y1) coordinates in image plane at time t1 (x2,y2) coordinates in image plane at time t2 a angle to Z-axis in Y–Z plane of the fire spot b visual angle of the CCD camera o1 angle to Z-axis in Y–Z plane of Z1-axis o2 angle to Z-axis in Y–Z plane of Z2-axis recent years, with the increasing large space buildings, the suitability of sprinkler use in such large space situations has been challenged. Commonly, thermally activated sprinklers are not suitable for high ceiling space use. The height of the ceiling in large space will greatly affect the sprinklers so that they cannot provide effective protection. The main problem is the activation delays of the sprinklers in large spaces, particularly high ceiling spaces. For example, even a 5 MW fire on the atrium floor would not generate a smoke temperature high enough to activate the sprinklers on an atrium ceiling higher than 15 m [1, 2]. Due to the distance between the potential fire source and the sprinkler heads which are mounted near the ceiling, sprinkler activation may be too late to minimize the fire hazards or damage. Even the early suppression fast response (ESFR) sprinklers have the recommended height limit [3–5]. Moreover, the height may also affect how much water can reach the flame before vaporized or blown away by the fire plume [6]. In those large spaces where the combustible materials are distributed
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
299
dispersedly, it is also not very efficient to install many sprinklers to cover all these materials. Now, robotic fire monitor that can be automatically controlled by computer and can work as a linkage device in a fire detection and suppression system is becoming a more suitable solution. Liu et al. [7] and Yuan et al. [8] have done some early researches. Compared to a sprinkler, a fire monitor has many advantages. First, the most remarkable advantage is that the activation time of these fire monitors is much shorter than sprinklers. They are activated by the alarm signal given by the fire detectors which are much more sensitive than the sprinklers’ explosion glass bulbs. These detectors can be conventional fire detectors or gas sensors. Second, water stream from a fire monitor has a higher speed, a greater flux and a larger impulse so it is more effective for fire suppression. Its spot type suppression may sometimes avoid the consequent losses caused by sprinklers and will not cause a downward moving of smoke [9] to endanger the occupants in the building. Last, a typical fire monitor has a shooting range of 50 m long, which enables it to protect much larger area than a sprinkler. In this paper, a new fire searching and suppression system using such automatic fire monitors is described. These fire monitors are assembled into a larger fire detection–suppression system. After fire confirmation and searching process, the direction and elevation of the fire monitor can be easily calculated and suppression can consequently be executed.
2. Principle 2.1. Structure of the automatic fire monitor system The automatic fire monitor system is a fire detection–searching–suppression system [10] which consists of three parts: the fire detection module (including detectors and the detector controller), the fire monitor module (including the fire monitor, the fire monitor manual controller and the CCD camera) and the central control module (including the computer, data-sampling interfaces and communication interfaces). In this system (shown in Fig. 1), the fire monitor serves as a fire searching and suppression device in conjunction with the fire detectors. Once the detector is in alarm state, the fire detection module will give a fire alarm signal and the central control module will send a linkage signal to activate the corresponding fire monitor. The fire monitor module and the central control module accomplish the fire searching and suppression after the fire monitor is activated. An automatic fire monitor itself is much like a little barbette which consists of a chamber, a CCD camera, a motor, an electromagnet valve, a computer connection interface (RS485 and video) and a shell. At the end of the fire monitor chamber, a CCD camera is fixed which is used for capturing the spot images. The optical axis of the CCD camera is adjusted parallel to the axis of the fire monitor chamber. In large space condition, the two axes can be practically considered coincident. The electromagnet
ARTICLE IN PRESS 300
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
Fig. 1. Sketch of automatic fire monitor system.
Table 1 Technical specification of the water cannon Maximum operating pressure Operating pressure Flow rate Pivot range Pivoting speed Remote control Computer interface
16 bar (16 105 Pa) 8 bar (8 105 Pa) (lower pressure is allowable) 1200 lpm 80 ?+60 max vertical, 7100 max horizontal 9 /s RS-485 bus RS-232 (with a protocol conversion box)
valve and the motor inside the fire monitor shell are controlled by the computer via RS-485 serial communication interface. The former releases or holds the water jet and the latter drives the fire monitor chamber to pivot in left–right and up–down directions. Furthermore, the pivot angle of the chamber is fed back to the computer as an important parameter to the fire searching algorithm. The fire monitor has dual control modes. A manual fire monitor controller is used for manual operations at emergency situation. In case a fire is discovered by a human, the cannon can be operated manually by a trained personnel. In the automatic mode, multiple fire monitors can be controlled and switches between them are available. The main technical specifications of a typical fire monitor are shown in Table 1. 2.2. Fire searching method based on computer vision theory Computer vision tries to simulate man’s vision and reconstruct 3D scene with 2D images. Usually, at least two cameras are needed to construct a 3D vision system [11]. Baseline distance between the two cameras is essential to reconstruct 3D coordinates. The relationship between image coordinates and object coordinates
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
based on single fixed camera imaging system can be established as Xo xi ¼ f ; Zo Yo yi ¼ f ; Zo
301
ð1Þ
where (xi, yi) represent the image coordinates, (Xo, Yo, Zo) represent the object coordinates and f represents the camera’s focal length. Here we use only one CCD camera to construct a vision system according to the position change of the camera between time t1 and t2 when it is pivoting in Y–Z plane. Fig. 2 shows the coordinates system in our vision system. *
*
* *
*
The pivoting point of the camera–fire monitor system is the origin of X–Y–Z coordinate system. The camera’s optical center is the origin of the X1–Y1–Z1 and X2–Y2–Z2 coordinate systems. X–Y–Z, X1–Y1–Z1 and X2–Y2–Z2 are right-handed coordinate systems. In X–Y–Z coordinate system, o measures zero along Z-axis and positive by righthand rule with X-axis as the thumb direction. Thus we have o1o0 and o2>0. P(d,a) in the Y–Z plane is supposed to be the fire position in object space. From Eq. (1) we have Y1 Z1 ¼ f ; y1 Y2 Z2 ¼ f : y2
ð2Þ
Between object space coordinates and image space coordinates we have Y ¼ Y1 cos o1 Z1 sin o1 þ D sin o1 ; Z ¼ Y1 sin o1 þ Z1 cos o1 þ D cos o1 ;
Fig. 2. Coordinates built from computer vision theory.
ð3Þ
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
302
Y ¼ Y2 cos o2 Z2 sin o2 þ D sin o2 ; Z ¼ Y2 sin o2 þ Z2 cos o2 þ D cos o2 :
ð4Þ
Take Eq. (2) into (3) and eliminate Y1, the relationship between Y and Z has an expression ðy1 cos o1 f sin o1 ÞðZ D cos o1 Þ þ D sin o1 : ð5Þ Y¼ y1 sin o1 þ f cos o1 Take Eq. (2) into (4) and eliminate Y2, the relation between Y and Z has another expression ðy2 sin o2 þ f cos o2 ÞðY D sin o2 Þ þ D cos o2 : ð6Þ Z¼ y2 cos o2 f sin o2 Solution of Y and Z can be obtained from Eqs. (5) and (6), as shown in Eq. (7). Y¼
Dðy2 f tan o2 Þ½ðsin o2 sin o1 þ A cos o1 B cos o2 Þ=ðA þ BÞ D cos o2 y2 tan o2 þ f
þ D sin o2 ; Z¼
D ðsin o2 sin o1 þ A cos o1 B cos o2 Þ; AB
ð7Þ
where A ¼ ðy1 f tan o1 Þ=ðy1 tan o1 þ f Þ; B ¼ ðy2 f tan o2 Þ=ðy2 tan o2 þ f Þ:
ð8Þ
In the above equations, y1 and y2 are still unknown. Actually, they can be calculated from the pixel coordinates (i, j) of the images, because most of the CCD camera are of the same standard specifications. Suppose the CCD camera’s scanning area is known as H V pixels and h v m2, the relationship between [y1, y2] and [j1, j2] can be found. y1 ¼ ðj1 V =2Þv=V ; y2 ¼ ðj2 V =2Þv=V : Thus the fire position P(d,a) in the space is confirmed and expressed as pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d ¼ Z2 þ Y 2 ; a ¼ tan1 ðY =ZÞ:
ð9Þ
ð10Þ ð11Þ
2.3. Working process Initially, the fire monitor is set at the horizontal-left limit position. Once a fire is detected by a fire detector in the system, the corresponding fire monitor will be activated. It will start searching for fire and be driven to the down-right limit position step-by-step (shown in Fig. 3). The fire monitor rests for a short time after each step. During this period of time, continuous images are captured from the CCD
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
303
Fig. 3. Fire monitor’s scanning process. 1: horizontal-left limit; 6: down-right limit.
I
II
t1 fire monitor pivot
fire monitor pivot
y x IV
III
t2
fire monitor pivot
Fig. 4. Aiming process when a fire is detected.
camera and sent into computer to be processed by image fire detection algorithm [12]. In the searching process, the robotic fire monitor scans in horizontal direction for three times however, each time in a different vertical angle. If no fire is detected in the entire searching process when the fire monitor reaches its down-right limit, it will be reset to its initial position. Otherwise, the locating algorithm is employed. In the locating algorithm, the distance between the fire monitor and fire is calculated. The step angle of the fire monitor is chosen as b (less step angle can be chosen) which is the visual angle of the CCD camera, thus no protection area is skipped. By pivoting the fire monitor, we perform the calculation by the displacement at different time. Images I, II, III and IV in Fig. 4 show the searching and aiming movements.
ARTICLE IN PRESS 304 *
*
*
*
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
First, when a fire region is detected on the image, mark the region and its gravity center. Move the fire monitor and mark the fire region repeatedly until the fire region reach the bottom edge and x-center of the image. Second, the vertical pivot angle of the fire monitor at this time (t1) is recorded as o1. Move the fire monitor vertically until the fire region reach the top edge of the image. Third, the vertical pivot angle at this time (t2) is recorded as o2. Move the fire monitor vertically until the fire region is at the center of the image. Thus combined with step two, the coordinate systems as shown in Fig. 2 are formed. Last, now the fire monitor nozzle is pointed right to the fire, record the vertical pivot angle as o3.
Now the distance d between the fire and the fire monitor can be calculated from computer vision theory with the aforesaid coordinate systems. Longer baseline yields more accuracy in fire location, so in image II and image III, the fire region is moved from one edge to another so that |o2o1| is as large as possible to achieve long baseline. 2.4. Suppression characteristic Above describes the fire searching process. To shoot the fire with water stream, change the elevation of the chamber according to d, a, o3 and water pressure. After the water pump is started up, the fire monitor can spray once the electromagnet valve is opened. While spraying, the chamber will swing in about 75 in all directions to fully cover the fire region. The diameter of water stream can be adjusted according to distance and environment in order to achieve best suppression effect. The maximum detection distance of the CCD is 100 m and the maximum spray distance of the fire monitor is 50 m. The protection area is considerable for the application in large space. By proper installation of multiple fire monitors, the protection area can be almost fully covered. Fig. 5 shows the protection area. The vertical limit of the fire monitor is 80 , so there will be a dead area right below each fire monitor. Usually the dead area can be ignored because it is relatively small. For example, a fire monitor mounted at 8 m only has a dead area of about 3.1 m2.
Fig. 5. Protection area of the fire monitors.
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
305
3. Experiment Experiments were conducted in a large test hall which is 30 m high, 30 m long and 18 m wide. The fire monitor was installed on one wall at the height of 6 m. Fuels in different tests were placed in a line on the ground of the hall every 2 m from the fire monitor (recorded as L). In each test, the fire monitor started its search from the horizontal-left limit. Water pressure is 4 bar. Different fuels, such as diesel oil, wood, and paper box are tested separately. Fig. 6 shows the experimental setup. Usually, the spraying lasts for 10 s and during this time the chamber will swing in 75 in all directions for 3 times. Table 2 shows the data for diesel oil fire tests. The fire is a 0.2 m 0.2 m pool fire ignited by flock. In all tests, the values of e are obtained by eyeballing and are of low precision. Searching time Ts varied in different tests, but usually it was less than 30 s if a fire is found. In the test data of the same fire type, all the former three Ts values were obviously greater than the later three Ts values. This was caused by the limitation of the CCD camera’s vision field since the fire monitor started its search from the same point in our tests. Fires farther than 16 m were detected in 1–2 scanning period (reference to Fig. 3) and fires between 10 and 16 m were detected in 3–4 scanning period (reference to Fig. 3) after the fire monitor chamber pivoted down. Generally,
Fig. 6. Experimental setup.
Table 2 Experimental data (diesel oil) Number
Fire type
L (m)
d=(h2w+L2)0.5 (m)
dc (m)
Ts (s)
e (m)
T (s)
1 2 3 4 5 6
Diesel Diesel Diesel Diesel Diesel Diesel
10.0 12.0 14.0 16.0 18.0 20.0
11.66 13.42 15.23 17.09 18.97 20.88
11.86 13.14 15.07 17.26 18.93 20.30
25.3 22.2 23.8 14.9 12.2 12.3
0.3 0.1 0.2 0.1 0.0 0.1
5.1 3.2 4.0 3.7 2.9 4.2
oil oil oil oil oil oil
ARTICLE IN PRESS 306
T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
searching time varied with fire position, fire strength and computation depth of our detection algorithm, which will not be further discussed here. Calculated distance and the actual distance are fairly accordant. The deviation is mainly due to the low precision of the pivot angle fed back to the computer. The angle measuring device in the fire monitor is quite simple and the motor gears also have mechanical errors. Extinguishing time T is usually smaller than 6 s because the fire strength in our tests is very small while the water flux is relatively large. Generally, larger e caused longer extinguishing time. Usually, if the water stream dose not hit the fire spot initially, it will cover the fire spot while the fire monitor is swinging.
4. Conclusion Fire searching and suppression were combined together and realized automatically in the automatic fire monitor system. Displacement and pivot angle of the CCD camera in fire searching process are the essential parameters to calculate the space coordinates of fire. Once the direction and the distance of the fire are obtained, the horizontal pivot angle and the vertical elevation of the fire monitor can be calculated according to water pressure. The fire searching precision is enough for practical use and the suppression effect is also satisfactory. Remote and automatic control of the fire monitor improves its efficiency and adaptability. Moreover, it provides more safety in fire fighting and is very economical when incorporated with fire protection system for large spaces use. Instead of installing multiple layers of sprinklers, the application of the fire monitor will not influence the inside sight of the buildings. It can be very useful to apply this technology in large spaces such as large museums, palaestras, showplaces and storehouses.
References [1] Chow WK. Performance of sprinkler in atria. J Fire Sci 1996;14(6):466–88. [2] Gott JE, Natariani KA. Analysis of high bay hangar facilities for detector sensitivity and placement. Society of fire protection engineers. Honors Lecture Series, May 20, 1996, Proceedings. Engineering seminars: Fire Protection Design for High Challenge of Special Hazard Applications, May 21–22, 1996, Boston, MA, 1996. [3] Hankins J. ESFR sprinklers–the facts you should know. Fire Prevention and Fire Safety Eng J 1995; 2(6). [4] Kung HC, et al. Early suppression fast response (ESFR) sprinkler protection for 12 m high warehouses. Proceedings of the Fifth International Symposium on Fire Safety Science. Melbourne, 1997. [5] Yao C. Overview of sprinkler technology research. Proceedings of the Fifth International Symposium on Fire Safety Science. Melbourne, 1997. [6] Chow WK. Full-scale burning facilities for atrium fire research. Fire Safety Sci 1993;2(2):61–4 [in Chinese].
ARTICLE IN PRESS T. Chen et al. / Fire Safety Journal 39 (2004) 297–307
307
[7] Liu Shenyou, et al. Automatic orientating fire extinguishing monitor. China Safety Sci J 2001; 11(2):37–41 [in Chinese]. [8] Yuan Hongyong, Chen Tao, Su Guofeng, Liu Binghai. Fire location and suppression with automatic hydrant in large space. Second NRIFD Symposium—Science, Technology and Standards for Fire Suppression Systems, Proceedings. Tokyo, Japan: 17th–19th July, 2002. [9] Cooper LY. The interaction of an isolated sprinkler spray and a two-layer compartment fire environment. Phenomena and model simulations. Fire Safety J 1995;26(1):1–33. [10] Fan Weicheng, Yuan Hongyong, Liu Shenyou. The integrated system for fire detection and extinction. Fire Safety Sci 1995;4(3):49–53 [in Chinese]. [11] Gao Wen, Chen Xilin. Computer vision—algorithm and principle. Tsinghua University Press: Beijing; 1999. [12] Yuan Hongyong, et al. Image type intelligent fire detection and location method. Safety Eng 1996; (3):17–19 [in Chinese].