A Video Image Smoke Detection System
Vol 20 No 4
Many facilities that face unique challenges in smoke detection are beginning to consider "Video Image Smoke Detection" (VISD) as a possible solution. VISD is a budding technology that processes closed circuit video images with custom software to recognize the presence of smoke. Developed primarily for the industrial and transportation infrastructure in Europe, VISD requires an engineered approach to adapt its potential for the life safety market in the United States. This article will leave operational details of the product to others, and elaborate on the engineering concerns of implementing a VISD system.
VISD operates on principles quite different from the more traditional forms of smoke detection. Therefore the engineering procedures also require a specialized approach. The flow chart in Figure 1 illustrates the first phase of engineering that addresses the applicability, operability and acceptability of VISD for its intended use.
Initial questions, while quite general, require detailed investigation to assure that VISD will work effectively, The questions include, but are not limited to, the following:
? Is VISD the most appropriate technology for my application ?
? Is my Facility suitable for VISD installation ?
? Will my application require acceptance by authorities representing the fire or life safety codes?
? How will my staff use and maintain the VISD system ?
? What systems can benefit from interconnection with the VISD?
A detailed engineering assessment should be performed to address these and other concerns before detailed designs are developed, installation is commenced or equipment purchased.
During this first phase any and all code and standards issues should be broached with the authority having jurisdiction (AHJ) for fire alarm systems. Where the VISD system stands alone and operates as either a security system enhancement or industrial safety system, AHJ involvement may not be necessary. However, if the VISD system will operate as the required smoke detection or is connected to the facility fire alarm system, consultations with the AHJ should be initiated by the engineer. Should current efforts to list VISD as smoke detection with recognized testing laboratories be successful, and NFPA 72 (National Fire Alarm Code) includes this new detection method in the 2006 edition, AHJ acceptance will become easier to obtain.
After application, facility and regulatory concerns are satisfactorily addressed, then the design can proceed. For an existing building or location (i.e. not new construction), a preliminary site test can be conducted. This test should be conducted in the areas of the facility and under similar lighting conditions as is anticipated. This provides an opportunity to evaluate any special cameras or lenses that may be under consideration for the design phase. If the performance of the selected equipment in the preliminary site test is successful, then the design for the system in the existing facility can proceed, and the process moves on to the flow chart in Figure 2.
The number of cameras and placement of equipment is the first stage of the layout. Figure 3 shows a schematic diagram of equipment for an eight camera configuration. Locations and routes for all the equipment and circuits shown must be shown in the design. Power supply sources and circuit routes must also be determined. If special camera or lighting conditions warrant any specific equipment, then the specifications must detail this. And, finally, care must be taken to assure all equipment and circuits are appropriately supervised.
Design of the system requires expertise in fire initiating device coverage and video system specification. Camera placement must permit adequate camera performance for the specified coverage area. Placement of the CPU, interfacing system connections, circuits, and other components should consider standardized supervision and survivability practices. Finally, the specification of equipment must not only be suitable for the software vendor, but must also perform reliably for the duty and environment of the intended application.
As for procurement of a VISD system, selection of the software vendor is presently limited to a few companies. Providers of the camera components and circuit installation, should be restricted to qualified digital video contractors and manufacturers. In the wide-open arena of video installation, there are shoddy equipment vendors and "trunk-slamming" contractors who offer installations "too good to be true." Construction documents should provide enforceable specifications and layouts, as well as qualification requirements for installing contractors.
The flow chart in figure 2 lists an "extended software test" as a desirable step in the installation process. If this test can be conducted, then the commissioning or "start-up" of the completed system can be facilitated. An "extended software test" consists of putting the VISD system into service, and digitally recording the image and system performance over an extended period (typically one to two weeks). The images recorded should include activities and conditions similar to those that the system will observe when in operation. This permits the software technician to adjust the sensitivity and performance of the system prior to commissioning. With digital recording, the images can be replayed until optimum settings are determined.
Acceptance testing and commission of the completed system must be performed to the satisfaction of all interested parties. The owners and operators are, of course, foremost among these. Even when AHJ involvement is not required, working with the AHJ to develop satisfactory performance evaluation methods can be productive. As the adopted codes have not yet addressed testing requirements for VISD, developing a consensus on the operational testing can yield technical benefits and enhance operational understanding.
Installation of a new technology such as Video Image Smoke Detection requires both adherence to proven engineering methods and developing innovative procedures. If conventional design and con-struction practices are applied without consideration of the unique characteristics of technology, the installation can surely be difficult. Conversely, customizing the engineering approach will permit emerging technologies such as Video Image Smoke Detection to take their place, solving the fire protection challenges of the 21st Century. o
Kenneth Gentile is a Professional Engineer and Senior Consultant in the Houston Office of Rolf Jensen & Associates. Mr. Gentile can be reached at firstname.lastname@example.org.