An automatic fire searching and suppression system for large spaces

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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 d c 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 (i 1 , j 1 ) pixel coordinates of a fire in the image at time t 1 (i 2 , j 2 ) pixel coordinates of a fire in the image at time t 2 H maximum pixel number per row of the CCD h actual width of the CCD T time of extinguish after the water is issued T s 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 X 1 –Y 1 –Z 1 camera coordinate system at time t 1 X 2 –Y 2 –Z 2 camera coordinate system at time t 2 (X,Y,Z) coordinates in X-Y-Z coordinate system (X 1 ,Y 1 ,Z 1 ) coordinates in X 1 -Y 1 -Z 1 coordinate system (X 2 ,Y 2 ,Z 2 ) coordinates in X 2 -Y 2 -Z 2 coordinate system x–y image plane of the camera (x,y) coordinates in x–y image plane (x 1 ,y 1 ) coordinates in image plane at time t 1 (x 2 ,y 2 ) coordinates in image plane at time t 2 a angle to Z-axis in Y–Z plane of the fire spot b visual angle of the CCD camera o 1 angle to Z-axis in Y–Z plane of Z 1 -axis angle to Z-axis in Y–Z plane of Z 2 -axis o 2 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
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