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During our “Foreign Body Prevention Strategies” webinar, industry experts discussed metal and metal detectable plastic detection, x-ray inspection, and other foreign body control strategies commonly used in the food industry.
Deb Smith, our Global Hygiene Specialist, and Robert Rogers, Senior Food Safety & Regulation Advisor from Mettler Toledo, answered questions both during and after the webinar. Below are 10 of the questions and answers we thought you might find interesting. Some questions have been edited for brevity and clarity.
Yes, typically, food products must meet the compliance standards and regulation requirements of the country or territory where it will be sold and consumed. For instance, Health Canada considers 2.0 mm (about 0.08 in) as the threshold size for consideration as a health risk. Please check out this CFIA link: Reference Database for Hazard Identification - Physical Hazards (inspection.gc.ca) for further information. Such physical materials may include glass fragments, plastic pieces, rubber chunks, metal shavings, animal debris, etc. In certain cases, there are exemptions and other physical hazard considerations to take into account, e.g., the hardness and shape of the material, the material type and source, etc. Standards may also specify even smaller or zero-tolerance of foreign bodies for vulnerable consumer groups such as infants and the elderly. So, it’s always best to just check and make sure you are meeting all the required compliance standards and regulations.
Typically, detection of wood is not possible or even reliable via x-ray. Wood is hard, but it is not dense—in fact, it is rather porous. Due to the low density, wood does not absorb much x-ray energy, making it difficult to identify at the high speeds at which production occurs. Wood may be visible to the human eye as a dark shade in an x-ray image, if analyzed in detail. However, this shading is often missed by detection machines at high process speeds.
A detectable band-aid usually has a small aluminium strip underneath its pad. As a non-ferrous metal material, aluminium falls in the middle of the metal detectability spectrum, so it is not as easy to detect as ferrous materials, but it is not as difficult as stainless steel. Regarding the use of x-ray detection, aluminium has a low density and is therefore difficult to identify using this equipment.
Additionally, aluminium on the periodic table is placed right next to silica (which most glass is made of); hence, they have similar specific gravities. Therefore, from an x-ray perspective, the aluminium strip in the band-aid, like glass, is particularly challenging to detect.
Full solid band-aids are usually detectable using both metal and x-ray detection systems, but if they go through processing and are broken up into smaller pieces, they may become undetectable. It is recommended to always look first at how you want to set up the system to successfully run the production and then challenge it with the band-aid in the most difficult situation. This will enable you to see what the possibilities are of detection when the system is set to successfully run the product, rather than setting it up to see the band-aid and then living with how it runs the product.
Mettler Toledo is frequently asked by organizations to perform detectability tests on a diverse range of materials. The company is more than happy to run these materials through our various systems.
The work we did for Vikan was regarding the detectability of metal detectable plastics, and to assess whether the metal detectable plastics were detectable in a food matrix under a range of conditions. These are the things you really need to look at.
The situation can get quite complicated as, in some products, detection is very easy because of the product conditions, but in others, it may just not be feasible to detect anything at all. We are very pleased with the way Vikan handled their *testing, not only looking at the detectability of various metal detectable plastics, but also looking at the effect that the metal detectable additives have on the material itself, in some cases making it more brittle, and possibly increasing the risk of foreign body contamination as opposed to lowering it. We are happy to undertake tests like these for anyone. Please feel free to contact me directly to discuss, at: email@example.com.
*Further information about the investigations conducted by Vikan and the testing conducted by Mettler Toledo can be found here: https://viewer.ipaper.io/vikan/white-papers/metal-detectability/metal-detectable-white-paper-en/
To explain briefly, if you imagine when you make a brush in a traditional way, you take a block of plastic and then you drill it full of holes and then you fix the bristles in place with a metal staple and, if the brush is made well, those bristles will be very secure. However, if one of those bristles then gets snagged on equipment and pulled out from underneath that metal staple, it creates a gap, which means that the remaining bristles get looser, and are then more likely to fall out.
With Vikan’s Ultra Safe Technology (UST) brushware, each bristle is individually, fully moulded into the brush block, so if they get snagged, they will snap, but it does not affect the security of other bristles in the brush. Therefore, overall, the risk of bristle loss is reduced.
Here's a link to a document that explains it all for you: https://www.vikan.com/uk/services/vikan-blog/understanding-bristle-fixation-in-food-industry-brushware.
Great question. Appropriate calibration of the metal detector is essential to maximize detection of both metal and metal detectable plastics. However, it is impossible to calibrate a metal detector to detect both metal and metal detectable plastic fragments of the same size. If you calibrate the detector to reject a 1.5 mm diameter iron ball, the piece of metal detectable plastic it will reject needs to be significantly larger. For example, a 7 mm diameter ball of metal detectable Vikan plastic would be required to give a similar detectability to a 1.5mm diameter iron ball. That is about 400 times the size by volume!
Vikan can provide customers with metal detectable plastic calibration test pieces. These can be used in either of the following ways:
(a) Once the detector has been calibrated for metal detection, the metal detectable plastic calibration pieces can be used to determine the size of metal detectable plastic that will be detected under the same settings (these will be much larger than the metal fragments detected).
(b) If the metal detector is only being used to control metal detectable plastics, the test pieces can be used to calibrate the detector to reject the required size of metal detectable plastic fragment.
For further information, please visit Vikan’s metal detectable products information hub at https://www.vikan.com/uk/services/metal-detectable-products. Please pay special attention to the videos.
Metal detectors are often used as a CCP but should not be relied on as the only method of foreign body control. As explained in the webinar, metal detectors are designed to detect metal. However, there are other foreign body hazards that the machine will not detect or will have a limited ability to detect, including metal detectable plastics.
Remember that even the best metal detection system that is correctly calibrated and includes a good rejection system will not be 100% effective. There are many other factors that can affect their detection performance so taking steps to prevent foreign body contamination at every stage of production is recommended.
Yes, as the “soft” product is more conductive than the hard frozen product. The increased moisture in the thawed product increases the conductive nature of the product and can generate extra signal to the detector. Detection capabilities are limited by the product itself not the detectors capability.
Yes, any circumstance where you have conducted a comprehensive risk assessment and determined that metal detection is the most appropriate control for metal detectable plastics. It all boils down to risk assessment. There might be occasions when you use a piece of equipment e.g., metal detectable pens, that are necessary in the food production area but have a high likelihood of falling into the product. As a single item, the pens are large enough to be detected when they pass through a metal detector. Similarly, items like scoops and scrapers made entirely of metal detectable plastic can be used. If these were to fall into the product, they are big enough to be detected, and even if they get broken down into smaller pieces, these pieces would be large enough to also be detected.
What we are trying to make people aware of is that it is the small fragments of metal detectable plastic, that are less likely to be detected, if they are detected at all. There are occasions when metal detectable plastic equipment is particularly useful in terms of foreign body risk control, but you just must think about its use in terms of risk and detectability in relation to your production operation and the food product in question.
Metal detectors react to conductive materials. However, most wood, plastics, rubber, etc. are not detectable unless there is an additive involved, e.g., graphite in rubber or plastic makes it more conductive; a metal nail in wood makes it more conductive, etc. On the other hand, x-ray detectors work by analyzing differences in material density and may be useful for the detection of high-density wood and plastics.
However, the best way to prevent most foreign bodies in your food product is to eliminate them from your production area and take further appropriate steps to minimise their presence in food before using the various detection and rejection systems.
Disclaimer: The responses given to these selected questions are the professional opinions of the industry experts involved and are not necessarily endorsements of any of the products and services mentioned. Companies should conduct their own site-specific risk assessments and develop their own hazard controls as part of their food safety plan.
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