Space requirements and layout
The portal metal detector, also called a walk-through detector, is a stand-alone structure that resembles a deep door frame (exhibit 3.1). The typical walk-through detector will take up a space on the floor about 3 feet across and 2 feet deep. (This does not mean that if you have a 3 feet by 2 feet space at the entrance to your facility you necessarily have space for using a walk-through detector.) The typical height of most portal detectors is around 7 feet. Weight of a unit can vary from around 60 pounds to as much as 150 pounds; however, the awkward shape of most portals prohibits their being easily moved by one person. Portals are generally freestanding and are rarely attached to the floor or surrounding structures. Power requirements are for one plug to a typical 110-volt wall outlet.
The first space factor to take into consideration is where people who are waiting to walk through the portal
(scannees) will stand. Ideally, there would be no wait for use of the portal, but this is probably unrealistic in a school environment where the entire population of students will be arriving over a very short period of time. Each school has to determine how many scannees will arrive and at what rate. Most detection programs will need to operate indoors, or at least under some type of shelter, and most schools are going to want to provide a comfortable environment for those waiting. This usually means that there must be enough shelter for the queue of scannees that might build up at any one time and that they should not be overly crowded. There should also be some way of clearly forming a line for scannees to stand in if they will be arriving at a much greater rate than can be processed; eliminating the opportunity for cutting in line would clearly be important in a school to reduce possible fights.
To avoid sending conflicting signals to the detector, the scannee waiting in line to use the portal next should be kept back 3 feet from the current user walking through the portal. Operators of the equipment and scannees who have already walked through also need to be at least 3 feet from the portal in all directions. (Contrary to a scene in a popular movie of several years ago, a gun thrown along the outside of a metal detector by the scannee before entering the portal and retrieved on the other side after the scannee got through would cause an alarm.) Likewise, if more than one portal metal detector is being used, each needs to be at least 10 feet from the others unless they have been synchronized.
Without very special instructions and limitations for the scannee population, it would be most difficult to conduct a metal detection scanning program with only the use of portals. Hand-held scanners are usually required for use on scannees who have triggered an alarm walking through the portal but who fail to be able to immediately determine what object on (or in) the person caused the alarm. Also, it is highly recommended that any routine metal detection program incorporate the use of x-ray equipment for bookbags and purses because of the ease with which a contraband item or material could be hidden within carried baggage. (See the sections in this chapter on hand-held metal detectors and x-ray equipment for baggage.) This equipment mandates additional space.
Space for the scannee to follow procedures is also required. A person about to walk through the portal needs room to place his or her carried items on the x-ray machine, room to put his or her pocket items (coins, keys, heavy belt buckles) in a special pass-through container, space to pick up these items, and space to turnaround to walk through the portal a second time if necessary.
It is very important that there be neither space nor opportunity for particular members of the population, including employees, to walk around the detection system (exhibit 3.2). Very definitive boundaries must be established to prevent circumvention of the system and prevent passback of contraband, where such prohibited items are handed from outside the screening area to those who have already successfully cleared the scanning process.
In designing the layout of the metal detection system, the composition of surrounding walls, furniture, nearby electromagnetic equipment (such as an elevator), nearby plumbing in the walls, and even metal trash cans must be taken into account. The optimal effectiveness of a portal metal detector can be easily degraded by a poor location, a casually placed metal stool, or the nearby use of electromagnetic devices. See the section about sources of interference elsewhere in this chapter.
In schools, the metal detection equipment and personnel will generally be located directly within the front or main student entrance. Unfortunately, the design of most schools does not lend itself to a comfortable staging area for this process. There is usually not nearly enough interior or covered space to allow for all the students waiting to enter the system. This may mandate that the metal detection staging area be located further within the facility, which may place administrative offices outside the cleared area. Conscious decisions must be made and potential risks must be realized when designing the weapon detection program.
A greater problem is often that the layout of schools will not allow for the limiting of only one or, at most two, entry points. Few schools can afford to have multiple entry setups with complete metal detection programs. The cost of the equipment would be quite high, but not nearly as prohibitive as the manpower to run these multiple systems.
Research Report: The Appropriate and Effective Use of Security Technologies in U.S. Schools