Issue 21: Flame and Smoke Video Image Detection (VID)
By Daniel T. Gottuk, Ph.D., P.E.
Fire detection provides an essential component in many fire protection system designs. Fire alarm systems initiate public egress, start smoke control systems, and actuate fire suppression systems. The majority of fire alarm systems used today consists of various smoke detection technologies. These technologies include spot-type ionization and photoelectric detectors, air sampling smoke detectors, and linear projected beam-type smoke detectors. Fire alarm system designers also use optical fire detectors for rapid flame detection in applications ranging from off-shore oil drilling platforms to aircraft hangars. All of these smoke detection technologies continue to improve. One goal of improvement is to provide broader coverage and faster response to real fire sources while eliminating nuisance alarms. In addition, improvements include features that reduce maintenance, testing and installation costs.
An alternative detection technology that provides unique advantages over typical fire detection systems has been gaining acceptance and use. Computer processing and image analysis technologies have improved substantially over the course of the past decade. This rapidly advancing technology, along with an emphasis on video surveillance since the occurrence of events of 9/11 has propelled the development of effective video image detection (VID) systems for fire. Fire protection system designers initially employed these VID systems for use mostly in large facilities, outdoor locations and tunnels. However, video-based detection is being used for a broadening range of applications.1 For example, these systems are currently installed in electrical power plants, paper mills, document storage facilities, historic municipal buildings, nuclear research facilities, automotive plants, warehouse/distribution centers, and onshore and offshore oil platforms.
In general, a fire VID system consists of video-based analytical algorithms that integrate cameras into advanced flame and smoke detection systems. The video image from an analog or digital camera is processed by proprietary software to determine if smoke or flame from a fire can be identified in the video. The detection algorithms use different techniques to identify the flame and smoke characteristics and can be based on spectral, spatial or temporal properties; these include assessing changes in brightness, contrast, edge content, motion, dynamic frequencies, and pattern and color matching. As an active area of research, there are multiple VID systems in development; however, there are only about five systems that are readily commercially available. The capabilities of these systems vary from being able to detect only flame or smoke to being able to detect both as well as providing motion detection and other surveillance/security features.
Smoke VID systems require a minimum amount of light for effective detection performance, and most will not work in the dark. However, capabilities vary between systems. In general, low light cameras can enhance performance and some systems have been developed to operate in the dark using IR illuminators and IR sensitive cameras.2 Flame VID systems can operate effectively in dark or illuminated spaces, and some systems will have enhanced sensitivity to flaming fires in the dark.
There are two basic architectures utilized by VID systems. Due to limitations of video processing technologies, the initial systems consisted of multiple cameras (usually a maximum of eight), each with an analog cable connection back to a central processing unit that executed all video capture and alarm algorithms (Figure 1). The processing unit typically has relay contact outputs and the ability to send various alarm signals to standard fire alarm control units. The systems can also record still shots or video clips associated with any alarm event and can provide instantaneous video display to a monitor.
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| Figure 1. VID system with CCTV cameras individually processed by a central control unit that runs the alarm algorithms. |
Advancement in technologies has resulted in the second type of architecture where both the video processing and alarm algorithm execution are performed at the camera in a single, spot-type device (Figure 2), just like a typical optical flame detector. These fire detectors can have onboard storage of video and can be integrated on a closed-circuit system with an additional central processing unit, or it can be integrated as a spot detector on a standard fire alarm system. These devices can also be monitored remotely via network or internet connections. Video events of alarm conditions can be archived for each device and can be displayed automatically to monitors for instantaneous viewing.
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| Figure 2. Example of a spot-type flame VID device with camera and alarm processing in unit (courtesy of Micropack). |
The National Fire Alarm Code, NFPA 72,3 recognizes the use of flame and smoke VID systems. Per this Code, the installation of these systems requires a performance-based design. There are no prescriptive siting requirements. Flame VID systems are classified as radiant-energy sensing fire detectors and are treated similar to optical flame detectors. Due to the variability of VID system capabilities and the differences in alarm algorithm technologies, NFPA 72 requires that the systems be inspected, tested, and maintained in accordance with the manufacturer's published instructions. Currently, there are no systems that are UL listed, but three systems have been FM approved. These include a system that detects only smoke, one that detects only flame and one that detects both.
As noted, commercially available systems range in capabilities. They also vary considerably in their setup and manner of use. Some systems have little or no user definable settings and are almost plug-and-play, and some systems require a trained manufacturer's representative to customize the system to the application. Once set up, there is little maintenance required of a VID system. Similar to any field-of-view detector, the primary issue is keeping the optical windows clean and the camera position fixed and unobstructed. Most systems monitor the video image, such as low or exceedingly high light levels, video loss, significant image changes, or obscured camera images, and provide a warning if the image quality is degrading or not sufficient for proper detection performance. Currently, VID systems can be tested/checked in one of three ways: 1) using a target smoke or fire source, 2) feeding the system a pre-recorded image of a flame or smoke event, or 3) using a product-specific electronic device that directs a pre-set "light" signal to the VID detector.
VID systems provide unique advantages in a wide range of applications. One advantage these systems offer is the ability to protect a larger area, while still achieving fast detection. This is particularly unique for smoke VID systems compared to spot or beam smoke detectors. In many large facilities with excessive ceiling heights, designers find it impractical to use conventional smoke detection devices. VID systems are able to detect smoke or flame anywhere within the field of view of the camera; whereas conventional smoke detectors require smoke to migrate to the detector. Figure 3 shows an example of a large facility application. VID systems can also be used for outdoor applications, such as train stations and off-shore oil platforms.
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| Figure 3. Smoke VID system detecting smoke in a power plant (courtesy of axonX) |
The ability to use the basic hardware of the VD system (i.e., the cameras and wiring) for multiple purposes is clearly one of the primary advantages of this technology. Integrating video-based fire detection with video surveillance inherently minimizes certain installation, maintenance and service costs and can increase system reliability due to more frequent use of and attention to the video equipment. Providing fire protection for historic buildings poses many challenges to not disturb the historic features of the structure. Running wire and mounting devices of typical fire alarm systems is just not possible in many of these applications for both aesthetic and practical installation reasons. Many museums and historic buildings already have surveillance cameras installed, which makes the use of VID systems attractive.
Another advantage of VID systems is the ability to have live video immediately available upon detecting a pre-alarm or an alarm condition. Immediate situational awareness allows monitoring personnel to easily view the protected area to determine the extent of the fire and to more accurately identify the location. In the case of nuisance alarms, the live video allows better assessment and a more appropriate response to the event. Video archiving of events provides a means to diagnose fires and potential problems and a basis to make system adjustments in the case of fires or nuisance sources.
The potential for nuisance sources is highly dependent on the specific VID technology. Some systems have the ability to ignore areas of the field of view that may have potential nuisance sources, to adjust sensitivity and to adjust the persistence time of the event before an alarm signal is issued. Specific alarm algorithms have also been developed by manufacturers to avoid common nuisance events.
In an age of ever-increasing use of video for surveillance and security, the potential to utilize the video images for multiple purposes offers a number of advantages. The development of flame and smoke VID technology capitalizes on the need for video, but more importantly, it provides a significant step forward in fire protection. VID technology provides advantages in many applications that cannot be effectively covered by typical fire alarm systems. Besides the commercially available VID systems, multiple systems are being developed and investigated by a range of manufacturers. As the technology becomes more widely accepted, used and recognized in the codes and standards, fire protection engineers should consider the potential benefits of using flame and smoke VID systems in their fire protection system designs.
Daniel Gottuk is with Hughes Associates
References:
- Gottuk, D.T., Lynch, J.A., Rose-Pehrsson, S.L, Owrutsky, J.C. and Williams, F.W., "Video Image Fire Detection for Shipboard Use," AUBE '04 – Proceedings of the13th International Conference on Automatic Fire Detection, Duisburg, Germany, September 14–16, 2004.
- Zakrzewski, R.R., Sadok, M., and Zeliff, B., "Video-based Cargo Fire Verification System for Commercial Aircraft," AUBE '04 – Proceedings of the 13th International Conference on Automatic Fire Detection, Duisburg, Germany, September 14–16, 2004.
- NFPA 72, National Fire Alarm Code, National Fire Protection Association, Quincy, MA, 2007.
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