Metal detection is a fact of life in the food processing industry. Most processors, whether they process snacks, meats, grains or liquids, have either metal detectors or X-ray machines to detect and control metal contamination. X-ray machines are often the preferred choice because many food processors use metallized films as their primary packaging, eliminating a metal detector as an option. X-ray machines also have the added advantage of being able to detect and eliminate other foreign materials such as plastics, bones, stones and glass. In addition, they can be used to monitor fill weights, cap alignments and other issues.
There is an ongoing debate as to how metal detectors should be incorporated into food quality and safety programs. Still, some companies have determined metal detection should be a critical control point (CCP) in their HACCP plans. Others deem it part of quality management. For instance, if the end products are chopped or ground, and a hazard assessment determines a significant potential for metal contamination, the company will probably adopt it as a CCP. However, if a processor produces purées or juices, it might install an inline metal detection unit to not only look for metal, but also to protect equipment located downstream from the unit. Other processors base their decision not on risk, but on customer demands, meaning if a primary customer demands metal detection as a CCP, the processor will use it. 
The Food Safety Modernization Act also is a factor in how metal detection will be viewed in the future. Chapter 20 of the 4th Edition of the Fish and Fishery Products Hazards and Controls Guidance (Metal Inclusion) includes the implication that if metal detectors are used, that step in the process must be considered a critical control point, even if the risk is deemed insignificant. 
FDA will likely use the seafood document as a model for developing guidance for the rest of the food processing industry. While guidance documents help processors develop a food safety management system, FDA does not treat them as a “guide,” but as a bible. If a processor has a metal detector or X-ray machine in place and uses it to ensure quality, it must be able to clearly document why it is being used that way.
Processors also must ensure their metal detectors or X-ray machines are operating properly. Consequently, processors must work with the equipment manufacturer to ensure the unit is properly set up. For example, if small products, such as breakfast bars or hot dogs, are to be tested, the equipment can usually be set to low sensitivities: 1.0mm for ferrous metals, 1.5mm for non-ferrous and 2.0mm for stainless steel. But if the products destined for metal detection are 50-lb. sacks of cocoa or frozen cased goods, the sensitivities would be higher. Therefore, processors should obtain from the equipment supplier a letter clearly stating the minimum operating limits.
Also, X-ray units should be hard wired, and connection lengths should be minimal. Why? Longer cords can cause detector problems, and hard wiring the unit prevents plant workers from unplugging it. Plus, processors should take care when selecting test standards. For example, if the majority of the equipment or cutting edges in the facility are of one type of stainless steel, the test standard for stainless should be for that type. 
If a processor determines metal detection is a critical control point, it must ensure the metal detector (or X-ray machine) is properly validated and clearly demonstrate the unit will be able to detect test standards at all times and under all conditions. The validation studies must be documented and kept on file to help ensure the unit will properly control potential hazards. 
Although how a processor establishes an online monitoring program varies throughout the industry, generally speaking, the test standards should be done according to the following schedule: at startup (or at product changeovers), at set intervals during operation and at the end of the product run. However, most processors run their standards at intervals of one or two hours since testing at shorter intervals places less product in jeopardy.
But setting hard and fast test intervals can create problems with regulators and third-party auditors, especially if operators fail to run the tests as scheduled. To address this concern, some processors set up a program with the standards run at startup, the end of production and at least once during the shift, as well as testing at one- or two-hour intervals. Then, if they slip up and miss an hour, they will still be in compliance with what is documented.
Metal detection is used for both quality and safety reasons. FDA has established guidelines for hard and sharp objects, but the presence of any metal in a food product, even if it’s very small and does not pose a significant safety hazard, renders that product adulterated. In fact, most recalls are initiated because of very small bits of metal or plastic in food. 
Whether you use a metal detector or X-ray machine as part of your process, the equipment must be properly set up and validated. And these activities must be fully documented. FDA, your customers and the public have a right to expect only the safest possible products, and it’s every processor’s responsibility to provide them.