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Walk-Through Metal Detectors for Personnel
(Chapter 3   Metal Detection, Continued)

Throughput

A well-trained and motivated operator should generally be able to process between 15 and 25 people per minute through a portal detector. This does not include investigation of alarms, nor does it take into consideration intentional or unintentional delays that might be expected in a student population.

Assuming that scanning personnel are well-trained, a school's throughput is going to be driven by three things: (1) the number of devices, (2) the rate at which students arrive, and (3) the motivation of the students to cooperate and move through the system quickly and the ability of the school staff to make certain that scannees move along quickly. The breakdown of equipment or the arrival of visitors who are not familiar with the scanning routine will also cause a definite slowdown; the impact of this must also be considered by the school administration but is not taken into account here. (The need for backup equipment must be considered by each facility, whether the equipment is borrowed from the vendor or a pool of spare equipment is shared within a district.)

Exhibit 3.03Keep in mind that any population that is aware that it has to regularly go through the scanning process will soon compensate and adjust their routine. These adjustments will generally be that: (1) the population will attempt to take fewer prohibited items with them into the facility (hopefully), (2) scannees will learn which otherwise acceptable items in their possession will still cause an alarm and will tend to shy away from these items (except maybe in the case of students who wish to create a hassle and who are undaunted by any consequences for doing so), and (3) the population will allow for the additional few minutes in their schedule, perhaps even going so far as to come early enough to miss the main rush. Travelers flying out of busy airports know to allow for a few minute delay at the metal detection scanners and will not cut their arrival time so close that they miss their flight. Students will do likewise, whether they need to show ID cards at the front gate, go through a metal detection system or meet with their friends before class. However, unreasonably long waits of 15 minutes or more could result in staff, students, and parents alike reevaluating the need for a metal detector program. Nobody wants to add significantly to their workday, especially if they are not compensated for it. Employee organizations may bargain for extra pay for this additional at-school time.

Exhibit 3.04Exhibits 3.3 and 3.4 depict the average number of students that would be waiting at each 5-minute interval before school to enter the weapon detection system for a school population of 1,000 and 2,000, respectively. For these calculations, it was assumed that metal detection equipment is in good working condition and optimally laid out, operators are motivated and comfortable in their tasks, and students move smoothly through the process. The arrival rate resembles a school morning where the bulk of students arrive within a 10- or 15-minute window, perhaps resembling a school whose students rely primarily on buses for transportation. (Whether or not the assumed arrival rate is truly typical of student arrival times is unknown; its use here is for enlightenment purposes only.) The overall throughput is gauged in terms of the number of students who will be waiting to enter the metal detection process at any particular time. The assumption is made that the portal metal detector will be the bottleneck of the scanning process and that other supporting components of the detection program will be able to perform their functions in an equal or lesser amount of time (although this may not necessarily be true at a particular school, depending on its setup). It is also assumed that the process will be set up such that students who fail the initial portal screening will be immediately funneled to an alternative screening point and will not have to reenter or further delay those at the main entry portal.

For students prepared to clear the portal who have minimized alarm-causing items and materials in their possession, the actual processing time through a metal detection program should be less than 10 seconds. For students who are not prepared, the processing time may add an additional 3-5 minutes or more for scanning the body with hand-held metal detectors and/or manual bag searches. This does not include the additional delay of waiting to be scanned.

After carefully calculating the necessary metal detection equipment, space, and personnel, and making adjustments for individual school characteristics, the administration may realize that there simply aren't enough resources available to handle its students in an acceptable manner. Some schools have overcome these limitations by staggering the schoolday start times for students, thereby spreading out the school's limited metal detection resources. Unfortunately, schools that rely heavily on bus service may not be able to utilize this solution.

 



Research Report:   The Appropriate and Effective Use of Security Technologies in U.S. Schools