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Do you really understand your foreign body risk?

16 October 2016

The results of an investigation to assess the metal detectability of different metal detectable plastic fragments provided by different suppliers to the food industry of metal detectable plastic equipment.
The results of an investigation to assess the metal detectability of different metal detectable plastic fragments provided by different suppliers to the food industry of metal detectable plastic equipment.

Foreign body contamination can be a safety or quality issue and the repercussions for a business can be expensive and damaging. Debra Smith considers how suitable metal detectable products really are for use in the food sector. 

Metal detection is well established as a method for reducing the risk of metal fragments in commercial food products. Originally designed to detect ferrous (iron) containing, 100% metallic items such as bolts, screws blade fragments etc. However, metal detectors are now often used in the food industry to control a range of metallic foreign bodies – ferrous and non­ferrous – as well as metal detectable plastics. But, how effective are they at doing this?

Many food manufacturers will be unaware that the metal detectability of any metal-containing foreign body will depend on a number of things, including the metal content of the contaminant, both the quantity and type of metal; size of the metal containing contaminant; orientation of the metal containing contaminant; the food product – size and composition; food packaging; speed of the conveyor belt; the detector used and its calibration.

Each of these interfering factors will have an effect on the detectability of the metal-containing contaminant and the interferences are often cumulative.

Consequently, metal detection systems do not give 100% security, even with regard to the detection of totally ferrous metal objects and they are unable to detect non­metallic items such as bone, glass or stone. Metal detectable plastics which are often used in the construction of food industry standard utensils and cleaning equipment contain just a small percentage of metal detectable material. Consequently, metal detection systems will only work if the fragments of this equipment are large enough to detect (given other detector limitations).

Test pieces
Most manufacturers of metal detection equipment will provide ‘calibration test pieces’, to check the function of the detector against ferrous and non­ferrous metals. These are regularly used by food producers to verify the performance of their metal detection system. Some manufacturers of metal detectable plastic equipment will also provide a test kit that enables the food producer to identify what size of metal detectable plastic can be detected by their detector/in their product.

However, very few actually do this. More worryingly, research undertaken by Vikan in Denmark, to determine the metal detectability of a range of metal detectable plastics available to the food industry, showed that not all are sufficiently detectable.

Initial investigations were conducted in collaboration with Detectronic, a Danish-based metal detection system manufacturer. 

The research showed that, even without the additional interferences of product and packaging, the detectability of metal detectable plastics varies greatly.

None of the samples from Supplier 2 were detectable and even the best detected metal detectable plastics needed to be over nine times the size of the iron sample to generate a similar reading – an 11mm round piece of metal detectable plastic was required to generate a similar detection signal to a 1.5mm round piece of iron.

Appropriate selection
Consequently, if the use of metal detectable plastic equipment is deemed necessary, the selection of appropriately metal detectable plastic equipment is essential to minimise the foreign body risk from this source.

Based on these findings it seems unlikely that metal detectable plastic fragments would be detectable in a food product, especially given the other detector limitations, and that the plastic fragments are likely to be small.

To detect these small fragments the metal detector sensitivity would need to be set so high that most products would be rejected. Additionally, the research indicated that the use of metal detectable plastic equipment may, in fact, increase the risk of product contamination, due to the perception that their presence will be detected by the metal detector.

As an alternative to the use of metal detectable plastic equipment, it is suggested that plastic tools and utensils are regularly inspected and replaced to minimise the risk of foreign body contamination from this source, and that equipment of a contrasting colour to the food product be used to enable the plastic fragments to be more easily seen in the product.

Debra Smith is global hygiene specialist at Vikan.

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