Interested in linking to "Access Control"?
You may use the Headline, Deck, Byline and URL of this article on your Web site. To link to this article, select and copy the HTML code below and paste it on your own Web site.
The most frequently used technique is to require a sharp turn immediately in front of the barrier. When vehicle speed is reduced by 50 percent, the "hitting power" is reduced by four times. “Straight lines make for faster and easier approaches for vehicles,” Dickinson says, “so it's best to create curves on the access roads to your facility as a natural impediment to speeding cars or trucks.”
One of the most effective barriers is embedded in the ground (Figure 4), with the barrier sticking up. It is lowered to allow passage of authorized vehicles. Bollards (Figure 5) can protect property, such a control room building, or other assets such as a parked tanker, tank farm or guard shack. Bollards can be rigid or can be raised or lowered to let traffic pass.
In cases where you can’t completely surround critical areas with fences, you may need intruder detection systems.
Developments in video and infrared (IR) cameras are making it possible to monitor remote areas of the plant and remote sites, such as electrical distribution systems and transformers, or to respond to alarms from intrusion detectors.
Figure 4: POP-UP BARRIERS
Studies have shown that humans will lose interest and be unable to detect changes shown on screens if they are forced to stare for more than 20 minutes. In many cases, the first time operators or security personnel actually see what's on the monitor is when an alarm goes off. Then, if they want to see what happened in the 30 seconds or so before the alarm went off, they have to rewind the VCR or DVR.
Modern digital cameras have the ability to detect when an anomaly occurs--such as someone walking into the frame. The camera can trigger an alarm which will alert security personnel. Digital camera images can also be stored on a continuous basis by a video server, which can store as much video as you have disk space to use – typically a month for four cameras, or 12 cameras for 10 days.
The Littleton Water Department in Littleton, MA, has facilities spread across the community, including a treatment plant, four wells, and three storage tanks. “Our first step was to install intrusion alarms linked into our SCADA system, but this created a problem with false alarms,” says Savas Danos, General Manager of the Littleton Water Department. “That’s when we decided we really needed to see what was going on at our remote sites because it was a waste of time and money to physically check the site each time.”
Figure 5: BOLLARDS BLOCK BEAUTIFULLY
Modern video surveillance systems also can be programmed to respond to events. Security personnel can configure the video system to automatically pan and zoom in to a specific location if an alarm occurs, such as to where they might expect to see an intruder's face. The pan and zoom procedure can be triggered by the camera system, the video server, a proximity switch, infrared detector, or any other input. And, because all the video is archived continuously, security can configure it so that all images from, say, 30 seconds to a minute before an event occurs be saved automatically in the event video clip. This eliminates the need to rewind a VCR, and allows security people to replay the event as many times as they need to analyze what happened.
"Video images of events can be put on any HMI screen, such as the building control system, security system or plant control system," says Rubin. "Surveillance is no longer limited to a bank of monitors in a security office. Today, video images from around the plant and from remote areas can be captured, viewed by anyone anywhere, and then stored as a permanent record on a disk."
Good perimeter security keeps bad guys from breaking into the plant. But what happens if bad guys get into the plant legally, right through the front door?
Security operations that use closed-circuit television (CCTV) analog cameras to monitor areas of the plant or building face a number of challenges. These systems require dedicated networks, and their images are stored on videotape. More of a drawback is the fact that the systems require security personnel to watch banks of monitors (frequently still black-and-white). Boredom and human physiology start to work against the effectiveness of such systems pretty quickly.
ControlGlobal.com is exclusively dedicated to the global process automation market. We report on developing industry trends, illustrate successful industry applications, and update the basic skills and knowledge base that provide the profession's foundation.