Food Safety

May 27, 2021 | Sesotec

How to test foreign material detection systems: validation, verification & monitoring

In this article about testing contaminant detection and production inspection devices, Sesotec food safety experts explain the importance of validation, verification and monitoring and their role in ensuring the effectiveness of a foreign material control program.

For food manufactures and processors, product inspection and contaminant detection devices are an important part of an effective foreign material control program. In order to ensure the safety of their products, food industry businesses rely upon detection technology – often metal detectors and x-ray inspection systems – to identify physical contaminants and remove defective products from the production flow.

But just as production processes vary tremendously according to a plant’s products and scale, contaminant detection devices also differ. In order to safeguard consumer health, international food safety standards require that companies validate, verify and monitor their contaminant detection technology on an ongoing basis.

Validation, verification, monitoring: what they mean and how they differ

Validation, verification and monitoring are three distinct phases of testing product inspection devices. Each phase relates to a different period in a device’s lifecycle and uses different criteria to evaluate the effectiveness of the device within a given process.

Depending on the global food safety and quality standards applied, specific requirements for each phase of testing inspection devices may vary slightly. In this piece, we refer to the requirements laid out in IFS Food Version 7.

1. Validation: can my device achieve the intended outcomes?

In testing contaminant detection technology, validation refers to the initial processes of qualifying whether a device can adequately fulfill the specific, documented requirements of its intended use.

Validation takes place before a food company purchases and/or implements a contaminant detection system. According to IFS Food V7, validation requires “the provision of objective evidence.” This evidence takes the form of specific criteria, such as the probability of detection (POD) and the false rejection rate (FRR), which are determined and documented before testing begins.

For instance, after assessing the foreign body risks present in their process, a company may determine they require a metal detector that can detect metallic particles of a certain size with a POD no lower than 99.998% and a FRR no higher than 0.001%. Factors such as packaging, product effect and production line speed should also be taken into account. These metal detector sensitivity criteria are then documented and different metal detection devices are tested accordingly. Only the devices that perform according to these standards will pass the validation phase.

2. Verification: is my device performing as expected?

After a contaminant detection device has been implemented, verification refers to scheduled, periodic testing procedures designed to ensure the device continues to function as expected.

To be compliant with IFS Food V7, verification should take place annually and include a series of thorough control tests, training sessions for personnel and the complete documentation thereof. Beyond detection sensitivity, the verification process should also include controls to ensure the device is reliably separating defective and/or contaminated products from the production flow.

As it only happens once annually, IFS Food V7 stipulates that the verification process should involve tests and documentation that are more exhaustive than the regular monitoring protocols detailed in the next section.

3. Monitoring: is my process under control?

In regard to foreign material controls, monitoring refers to frequent, ongoing performance tests designed to assess whether any changes have taken place since the last test that could impact the performance of an inspection device.

Monitoring is a routine protocol carried out multiple times per shift, usually at the beginning and end of a shift and whenever a product or batch is changed over. According to IFS Food V7, monitoring consists of “a planned sequence of observations or measurements of control parameters.” Such observations and measurements include, among others:

  • ensuring the device is operating according to the correct settings
  • running a series of test pieces through the device to ensure they are rejected
  • ensuring the catch basin for rejected products has been emptied and nothing is obstructing the ejection chute

Monitoring processes must also be documented, though not with the same exhaustiveness required in the verification process.


The importance of testing product inspection systems

While validation, verification, and monitoring are distinct testing phases, all three phases are interconnected and serve broader food safety goals. These include, among others:

  • Ensuring food industry businesses implement contaminant detection technology that is appropriate and effective for their products and processes
  • Ensuring contaminant detection technology is consistently calibrated to perform with the necessary sensitivity
  • Promptly identifying variables that may impact the performance of a detection device, enabling businesses to make adjustments accordingly
  • Enabling thorough, ongoing documentation of food safety protocols  
  • Reducing the number of false rejects and thus the volume of wasted food
  • Facilitating compliance with food safety standards, such as IFS
  • Reducing the risk of undetected contaminants which could lead to costly product recalls

How to test your metal detectors and x-ray inspection systems

Monitoring the performance of your product inspection device is not only necessary in compliance with food safety standards, it is also essential for protecting your customers and your brand. The performance and sensitivity of your device can change over time and so thorough controls can help you identify and correct minor issues before they escalate.

Here is an overview of the steps involved in regular performance monitoring for metal detectors and x-ray systems:

1. Select a representative range of test pieces

Control procedures for x-ray inspection and metal detection devices should use a range of test pieces that are representative of the risks inherent in your process. Among these test pieces should be a few that represent the worst-case scenario: the smallest, most difficult to identify particles that could be present in your products.

X-ray and metal detector test pieces come in a variety of formats (cards, sticks, cubes, balls, etc.), materials (FE, NFE, V2A, etc.) and sizes, each of which are suitable for different processes and applications.

2. Use the correct test packaging & positioning

In the case of packing and filling lines, test pieces should be placed inside the same type of packaging as your products, be they glass jars, plastic trays or tin cans. Additionally, some test pieces should be placed inside the packaging in positions where the device sensitivity is at its lowest, such as the very center of the detector.

3. Select the appropriate control procedures

When it comes to control procedures, the number of tests you run, the frequency with which you run them and types of contaminants you test for are ultimately dependent on the requirements with which you must comply and the level of risk your company is willing to tolerate.

One of the quickest and most basic control procedures involves placing a series of test pieces (FE, NE, V2A) at different positions (front, middle, back) in three packages one after the other. These packages should be spaced at normal distances and flow through the metal detector at normal operating speeds to test whether the device can reliably eject all three packages in succession.

This procedure may be combined with other, more extensive procedures performed at different intervals.

4. Establish intervals for testing

As part of routine monitoring, controls should be carried out at the following times:

  • At the beginning and end of a shift or production cycle
  • At regular intervals during a product cycle, such as once every hour
  • Immediately following a batch or product changeover
  • After the settings on the device have been changed
  • After locating and correcting errors on the device
  • After maintenance or servicing on the device

5. Document your tests results in compliance with requirements

Different distribution networks, food safety standards and legal authorities have different standards for the documentation of ongoing performance controls. Sophisticated product inspection technology is equipped with software that can be programmed to automatically log and send test results to the responsible parties.

Conclusion: ensuring consistently excellent performance

Every food product and processing line is unique and brings its own particular set of challenges for foreign material controls. Extensive validation testing is necessary to choose a contaminant detection device that will reliably protect your products and ongoing verification and monitoring are necessary to ensuring the device continues to perform as expected. Because the ongoing testing of equipment performance requires a significant amount of time and resources, contaminant detection technology should be designed to simplify control procedures for companies.

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