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November 1, 2001
CCTV Surveillance in Schools
By Jeff Lupinacci
Many schools are installing CCTV (Closed Circuit Television) systems for security surveillance. Unfortunately these systems are being installed without a clear understanding of what benefits the site will receive, and how it will be supported. Mistakenly it is often thought that once cameras are installed all security problems will be eliminated.
Even the best designed and installed camera system is nothing more than a security tactic or tool to support a school security plan. In a typical school or office environment, cameras do not prevent an event from happening; they are usually used to review the event after the fact in an investigative manner. This is exemplified by the Columbine tragedy.
A solid security plan for a facility should be established that answers the question, "What are we interested in protecting?" If the answer is protection of personnel and property both internal and external to the building, you will need to assess your trouble spots. Are you more likely to have an assault in the parking lot or have equipment carried out the back door?
The configuration of the camera system needs to be based on a philosophy, such as recording the face of everyone entering the building. If you also want to record the face of a person leaving the building, presumably with stolen equipment, then you will need at least a second camera because the first will only view the back of the subject's head. If you also want general surveillance of long corridors, the images of persons at the far end of the corridor may be too small to identify, but might be adequate to see a person carrying equipment.
When trying to protect the exterior building perimeter, parking lots, utility connections, and other items outside, you must use exterior cameras. Exterior cameras are more expensive than interior cameras, because of the cabling pathways and weatherproof environmental housings. Exterior cameras also are required to dynamically adjust to a wide range of lighting extremes such as direct sunlight to "night vision." To obtain a usable image a DSP digital camera has the ability to balance the light in multiple zones within the image. Monochrome cameras (black & white) are better able to see in low light conditions and have better contrast. Some color cameras will automatically switch to monochrome when the available light drops in the evening.
The use of a pan/tilt/zoom (PTZ) camera is not an effective way to eliminate cameras. The cost for a PTZ camera is approximately three to five times the cost of a fixed camera. The typical PTZ cameras on the market are not able to view all 360 degrees at the same time. At best you are able to view 180 degrees, leaving 180 degrees unprotected. A person willing to cause a problem is often able to see where the camera is aiming and stay out of the line of sight. PTZ cameras are adjusted by human intervention, or by a signal from a motion detector or door contact. The human is not always available to move the camera; as a result events are not seen or recorded. PTZ cameras can be programmed to oscillate like a fan, but again it can be determined where the camera is pointed and the camera's view can be avoided. Also, oscillation creates a great deal of wear and tear on the camera motors and increases maintenance costs.
As the philosophy and facility dictate the number of cameras and their placement, it needs to be determined who will be reviewing the images and how will they be used. Is the system owner willing to invest in the personnel, supplies, and equipment maintenance to keep the system functioning correctly? When cameras are simply installed and forgotten they will soon fail. A common misconception is that the tape will automatically rewind and record over itself, therefore no human intervention is required. The use of analog tapes should not exceed 10 re-writes. After 10 re-writes, the recorded images are of such a degraded quality that they are extremely difficult to see. Often the owner will find out that the equipment failed weeks prior to an event that calls for a review of the tape. This is a common problem in banks where ATM machines are used. A customer takes money from their account and gets mugged in the process. The police ask the bank owners for the tape recording to review, which is when the bank finds out that the camera hasn't worked properly in months. Many lawsuits have been filed for events occurring in bank lobbies where the cameras provide patrons with a false sense of security.
Another important question is: How will the images be monitored and view? This will be a big factor in determining the flexibility of the system and of course the price of the equipment. The higher the quality and more features the equipment has will increase the cost.
At the lower end of the price spectrum is a multiplexer. This device is used to receive up to 16 different camera images and display them on the same screen simultaneously or individually. When the images are shown at the same time in a small square on the screen, they are not full motion video. They average less than two frames per second, so a person walking is shown as a series of still pictures two seconds apart. It can be thought of that the multiplexer's processor is working like a card dealer looking at each camera in succession, then returning to the first camera and beginning again. The benefits of multiplexing are that it allows all images to be viewed until more detail is required and that a specific image can be chosen to be viewed individually at full motion. The multiplexer also allows for all 16 cameras to have their images recorded on a single recording media.
At the higher end of the price spectrum is a video matrix switcher. A switcher allows for thousands of camera images to be controlled through a single keyboard. Each port can be turned on or off, and can be viewed at any frame rate up to full motion. Multiple sites can be networked together to allow multiple sites to be monitored from a single point. This set up is very common in casinos, airports, universities, or when an entire school district is to be controlled from a single site.
Studies done by the U.S. Military show that a person can only effectively watch a monitor for eleven minutes of each hour. If this time is divided by the number of monitors that are in a control center it is clear that CCTV can't be used to stay on top of all images all of the time. Thus, it is critical that images be recorded to be used as an investigating tool after an event has occurred.
Traditionally, the analog recording on Time Lapse Recording VCRs has been a mainstay in the industry, and costs the least. The problem with Time Lapse is that the tape is slowed to make it last up to 96 hours. If you are using a multiplexer and slow the recording down, you are effectively only getting a frame every three to ten seconds, and the images are at a low resolution, making it critical to change tapes often.
Digital recording is more expensive and has been around since approximately 1996. Digital recording systems benefit from the reduced cost for PC components and thus, make the cost of the security system more affordable for most organizations. A digital recorder can be programmed to record at frame rates up to full motion for all images. The digital recorders can dynamically change the frame rate when motion is detected in the screen. This is important to maximize your recording archive period; you don't need a full motion recording of an empty stair tower, only when there is a change in the picture caused possibly by a person walking through the scene. A digital recording system by nature doesn't experience degradation of the image resolution because the files are the stored in the same format as when they are recorded--1's and 0's.
There seem to be a lot of choices in CCTV systems, but the key is to decide how critical a tool the system will be to meet the goals of the security plan. Always obtain the services of an experienced design professional to determine camera placement, pathways, correct equipment selection, etc. Always dedicate adequate resources and capital to keep the system operating at peak performance.
Email: Jeffrey A. Lupinacci
Jeffrey A. Lupinacci, RCDD/LAN Specialist,
Sr. Telecommunications Designer, Brinjac Engineering, Harrisburg, PA
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