Ten questions to ask the walk-through metal detector salesperson.
1. Does the metal detector meet National Institute of Justice Standard 0601.02, "Walk-Through Metal Detectors for Use in Concealed Weapon and Contraband Detection"?
In January 2003, NIJ released a new standard to establish performance requirements and testing methods for WTMDs. The standard was developed for NIJ by the Office of Law Enforcement Standards of the National Institute of Standards and Technology. The NIJ standard is a difficult standard to meet, but those manufacturers willing to commit resources and engineering effort toward meeting this standard will produce a detector worthy of selection by any agency. Each agency/user must decide which object size and associated performance measurements outlined in the new NIJ standard are applicable to its particular operating environment.
2. Is the manufacturer an ISO-certified company?
Certification by the International Organization for Standardization (ISO 9000:2000 or 9001:2000) provides the purchaser with at least some confidence that every detector sold by the manufacturer is designed, developed and produced under the highest of quality assurance standards.
3. Does the metal detector use active or passive technology?
Active detectors have transmitter and receiver coils on one or both sides of the portal, which generate low-intensity magnetic fields toward the inside of the portal (although some of the field does extend beyond the outside of the portal walls). Modern, high-sensitivity, active detectors can detect a wide array of ferrous and nonferrous metals regardless of their size. Active detectors are susceptible to some electromagnetic and mechanical interference and have the potential to affect some medically implanted devices, according to recent studies by the Food and Drug Administration (FDA).
Passive detectors do not generate magnetic fields; instead, they measure changes in the earth's magnetic field over ambient background in the vicinity of the portal when ferrous materials are passed through the portal. This helps reduce false alarms caused by innocuous items such as tin and chrome badges, brass buckles, gold and silver jewelry, and nonferrous metals contained in coins. However, for those agencies that must be able to detect nonferrous metals (without steel) as well as ferrous metals (with steel), such as required in correctional and other high-security applications, the use of passive detectors is not advised. Inmates typically fashion prison-made weapons from a wide variety of metals, especially soft, nonferrous metals such as aluminum, and passive detectors will not be able to detect these weapons at all. Any agency contemplating the purchase of a metal detector using passive technology for high-security applications must determine if weapons produced from nonferrous metals can be a threat. If so, active metal detectors should be used.
4. What design enhancements has the manufacturer made to reduce the effects of outside mechanical and electromagnetic interference?
The common phrase "You get what you pay for" applies here. Some manufacturers of inexpensive metal detectors reduce interference by using thick aluminum portal walls and a cover at the top to shield against the effects of outside interference, while others increase the sensitivity by simply reducing the portal width down to a size that a person can barely squeeze his or her body through. Changing the physical features of the detector will not help if the manufacturer has failed to improve upon the detector's actual detection principles. Other manufacturers decrease the sensitivity only in certain areas of the portal magnetic field to reduce interference-induced alarms. Although those detectors may be able to meet old, outdated NIJ standards or other older agency-specific standards and specifications, that same detector will never be able to meet new requirements that are being implemented under more recent standards and agency guidelines. Before buying, ensure that the detector manufacturer has made significant improvements and developments in the digital-processing capabilities of the detector, developing a high-quality metal detector capable of offering a uniform magnetic field throughout the entire portal area and capable of detecting a wide variety of metals and objects without compromising its integrity.
5. Will vibrations in the floor or bumps to the metal detector's side panels disrupt or cause it to inadvertently alarm?
WTMDs are prone to mechanically induced interference. For example, outdoor detectors are susceptible to the effects of high winds. The manufacturer should provide a means to anchor the detector portals to the floor to reduce the effects of wind, vibrations and bumping. Metal detectors should provide the operator with a means to monitor or measure the actual effects of such mechanical interference on the control panel in order to determine appropriate methods for reducing the level of interference from these sources. Some detectors are programmable for environmental and surrounding mechanical interference to create a "signature" that the processor will remember, account for, and not respond to with an alarm. Recent developments by some manufacturers resulted in software enhancements that can negate the effects of false alarms caused by the detector when it is shaking or vibrating in the absence of metal objects passing through the portal's magnetic field. However, ensure that the software can discern between vibration-caused alarms and metal-induced alarms, while retaining the capability to detect a metal object passing through the field even if the detector is alarming from vibration and trying to compensate for that vibration-induced alarm.
6. Does the metal detector detect all types of metals?
Although this seems like an irrelevant question, there are, indeed, certain types of metals that cannot be detected by any detector. Other types of nonferrous metals, such as stainless steel, copper and brass, are difficult to detect depending on size and orientation of the metal object. The manufacturer should be able to indicate which metals will not be detected for each of the different programs that the detector has to offer.
7. How effectively can the detector discern nuisance metal items (coins, eyeglasses, zippers, etc.) from metal contraband objects?
The ability to discern nuisance metal items from legitimate metal contraband is one of the most important characteristics of an effective metal detector. If it detects nuisance objects too frequently, staff may lose confidence in the detector, leading to an inefficient flow of people through it. The higher quality, more expensive metal detectors will allow items such as coins, eyeglasses and belt buckles to pass through, while accurately identifying items that may be considered legitimate contraband items. More advanced metal detectors can be adjusted to a setting designed for specific environments such as airports, schools and prisons, where certain sets of threat object sizes can be designated.
8. Are there places in the metal detector's detection field (such as close to the floor or on top of a person's head) where objects may not be detected?
Often, manufacturers scale down the sensitivity near the top of the detector. That is because the processor on top of the portal emits its own electromagnetic interference, and, depending on how well the detector is engineered and insulated, the interference in that top portion of the field/portal causes the detector to alarm when no metal is present. So to compensate, the manufacturer lowers the sensitivity in that zone, thus creating a vulnerable spot where some threat objects may be able to get through the portal without detection, depending on the object size and metal type.
The same practice can occur with metal detectors that are particularly susceptible to the effects of steel reinforcement (rebar) in concrete floors. Again, manufacturers will lower the sensitivity in the bottom portions of the magnetic field in order to eliminate rebar-induced false alarms, thus creating vulnerable spots in the lower portions of the portal's magnetic field, specifically in the area of the person's shoes. More modern, high-quality detectors employ multiple detection zones, often overlapping each other, to ensure that weak areas of vulnerability in the portal detection field will be eliminated.
9. Has the metal detector been tested and can the manufacturer provide documentation that it is safe for use by all individuals?
It is important to make sure that the metal detector is safe for use by pregnant women, children, and individuals with active ambulatory medically implanted devices, such as cardiac pacemakers, neuro-stimulators and drug-infusion devices. Many manufacturers' brochures indicate such safety without verifying whether those tests were conducted by the manufacturer or by an independent lab and according to the most recent standards of the Institute of Electrical and Electronic Engineers (IEEE C95.1-1991) and other standards on human exposure to radio frequency electromagnetic fields.
Recent studies conducted by the FDA have indicated that detectors emitting pulsed, electromagnetic waveforms or having modulations within the passbands of some active medical devices have the potential to interfere with the operating frequencies of those medically implanted devices. The studies indicate that continuous wave detectors do not have the potential to cause interference. So the purchasing agency should inquire as to whether the detector uses pulsed or continuous wave technology. The FDA also found that active detectors have the potential to cause some heating of tissue in the fetuses of pregnant women. While these studies are in their preliminary stages, the findings are alarming, and it would be in each agency's best interest, from a liability standpoint, to ensure that the detectors it purchases now will be declared safe a year or two from now when the FDA's studies are complete. Manufacturers should be able to provide the purchaser with guidance in how the detectors should be positioned and operated by staff to reduce or minimize the exposure effects to bystanders and staff as outlined in the recent FDA studies.
10. What size portal width did the manufacturer use to qualify its detector against a certain set of performance specifications?
Some detectors come with 24-, 28-, 30- and 32-inch portals (interior measurements). If a manufacturer claims to meet certain specifications for a solicitation bid or proposal, the purchaser must make sure that the detector model and portal width being offered are the same model and portal width that was tested against and met the requirements outlined in the procurement specification or tested against a particular standard. Manufacturers may test a detector with a 24- or 28-inch portal that detects objects with certain programs and sensitivity levels because the portal width is much smaller. However, if the agency purchases a 30- or 32-inch portal model to meet certain requirements under the Americans With Disabilities Act, that particular model with that size portal may be much less sensitive and may not be able to detect certain specified threat objects. Or, the sensitivity levels may have to be significantly increased to compensate for the increased portal width, which will make the detector more susceptible to mechanical and electromagnetic interference.
Before purchasing a new WTMD, address the questions above to ensure a good investment. Furthermore, corrections officials should identify the intended location where the detector will be installed and have an awareness of the types of contraband that may be encountered at that location. For example, a metal detector designed for screening inmates' visitors may not be optimal for screening inmates leaving work assignments in a factory. By using these questions as a guideline, corrections officials can ensure that their next metal detector purchase meets the needs of the correctional facility.
Louis C. Eichenlaub is warden at the Federal Correctional Institution in Milan, Mich. John Ely is a management and program analyst in the Federal Bureau of Prisons' Office of Security Technology.
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|Title Annotation:||CT FEATURE|
|Author:||Eichenlaub, Louis C.; Ely, John|
|Date:||Oct 1, 2006|
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