W h i t e Pap e r
Myth-busting the metal detectability
of metal detectable plastics
Introduction
Metal detection is well established as a method
for ensuring the absence of metal fragments in the
food products sold to consumers. Rejection of food
products containing metal fragments aids both food
safety and food quality.
Metal detection systems were originally designed to
detect ferrous/iron containing, 100% metallic items.
However, in the food industry they are now used to
control a range of metallic foreign bodies, ferrous and
non-ferrous, and metal detectable plastics. However,
food manufacturers are often unaware that the metal
detectability of any foreign body will depend on many
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
• food product
• food packaging
• speed of the conveyor belt
• detector used
Consequently, metal detection systems do not give a
100% security.
Detectability of
metal detectable plastics
The metal detectable plastics used in the construction
of cleaning equipment only contain a small percentage
of metal detectable material. Consequently, metal
detection systems only work if the fragments of this
cleaning equipment are large enough to detect (given
other product and packaging considerations).
Most manufactures 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 the food
manufacturer to verify the performance of their metal
detection system.
Some manufacturers of metal detectable cleaning
equipment will also provide a test kit that enables
the food manufacturer to find out what size of
metal detectable plastic can be detected by their
detector/in their product. However, very few food
manufacturers do this. More worryingly, research
recently undertaken by Vikan, Denmark, to determine
the metal detectability of a range of metal detectable
plastics currently available to the food industry,
show that not all of these materials are sufficiently
detectable.
The work was conducted in partnership with
Detectronic, a Danish based metal detection system
manufacturer, using the equipment shown in Figure
1a. Figure 1b shows an example of a metal detectable
plastic test kit, as provided by some cleaning
equipment manufacturers, and Figure 1c shows the
results of the investigation.
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W h i t e Pap e r
Figure 1a. The Detectronic metal detection system used
to validate the detectability of different materials used in
the manufacture of metal detectable equipment.
Figure 1b. An example of a metal detectable test kit
(Vikan) often supplied with metal detectable equipment.
The results show that, even without the additional
interferences of product and packaging, the detect­
ability of metal detectable plastics varies greatly. The
selection of appropriately metal detectable plastic
cleaning equipment is therefore essential to minimise
the foreign body risk from this source.
6
Voltage
5
4
Sample 2 test pieces and samples of 0.60mm and 0.35mm ‘metal detectable’
filaments were undetectable under these assessment conditions.
Detectronic model No. 606-250
Speed: 20 meter/minute
Settings: Neutral product
Product compensation: -5
Fe/Iron
Vikan
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Sample 1
Figure 1c.
The results of an
investigation to assess
the metal detectability of
different metal detectable
fragment sizes provided
by different suppliers to
the food industry of metal
detectable equipment.
(Vikan/Detectronic, 2012).
Sample 2
Sample 3
2
Sample 4
Filament 0,6 mm
Filmaent 0,35 mm
1
8 sizes of test pieces from each supplier (competitor 1‐4)
0
1,5 mm 2 mm
2 mm
(round) (square) (round)
2,5 mm
(round)
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3 mm
(round)
3,5 mm 4 mm 4 (round) 6 mm
6 mm
(round) (square)
(square) (round)
7 mm
8 mm
8 mm
(round) (square) (round)
10 mm
(round)
11 mm 20 mm
(round) (square)
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W h i t e Pap e r
Detectability of metal detectable
plastic filaments
The most recent addition to the metal detectable
product range offered by some cleaning equipment
manu­facturers is the metal detectable brush, incor­
porating ‘metal detectable’ plastic filaments. As for
the fragments of the metal detectable plastics, the
detectability of the filaments in these brushes will
depend on a number of factors, including;
• the metal content of the filament, both quantity and
type of metal
• the diameter/thickness of the filament
• the size of the filament fragment
• the orientation and position of the filament in the
food product
• the conveyor speed
• the food product
• the detector used
Additionally, the data shown in Table 1 (Lock, 1990),
indicates that, to achieve a similar detection to that of
a ferrous ball with a spherical diameter of 1.5mm (see
Figure 1c), metal wire lengths of between 3mm and
8mm would be required. Currently brushes with metal
detectable filaments are only available with filament
diameters of 0.35mm, 0.5mm and 0.6mm, i.e. much
thinner than the metal wires assessed in Table 1. It can
be concluded therefore that even longer lengths of
metal detectable plastic filaments would be required
to achieve the same level of detection.
Based on the information given above it seems
unlikely that metal detectable plastic filaments/
filament fragments would be detectable in a food
product, especially given the other product and
packaging considerations, and that the filament
fragments are likely to be small. To detect these
small filament fragments the metal detector sensitivity
would need to be set so high that most products
would be rejected.
Additionally, with regard to brush filament thickness,
only relatively thick metal detectable filaments
are currently available, i.e. there are no 0.15mm
or 0.25mm metal detectable filaments currently
available, probably because these would be even
less detectable. However, fine filament brushes are
more effective at removing fine powders (including
allergens) and, consequently, the use of brushes with
thicker filaments may actually increase the risk to the
consumer due to poor cleaning. The use of thicker
(harder) metal detectable filaments may also increase
the risk of injury to the consumer if present in the food
product.
As an alternative to the use of metal detectable
plastic filament brushes, it is suggested that brushes
should be regularly inspected and replaced, in order
to minimise the risk of foreign body contamination
from this source, and that equipment which is of a
contrasting colour to the product be used to enable
the filament to be seen more easily in the product.
Table 1. Lengths of metal wire required to obtain a similar
level of metal detection to that of a 1.5mm spherical
diameter ferrous ball (see Figure 1c). (Lock, 1990).
Ferrous ball
(spherical diameter)
Pure Steel paper clip
(ferrous) 0.95mm
cross-sectional diameter
Pure Copper wire
(non-ferrous) 0.91 mm
cross-sectional diameter
Pure Stainless Steel wire EN
58/AISI 304L (part-ferrous),
1.16 mm crosssectional diameter
1.5mm
3mm long
9mm long
8mm long
2mm
6mm long
26mm long
24mm long
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W h i t e Pap e r
The BRCv6 and the use of
metal detectable equipment
The BRC Global Standard is a leading food safety and
quality certification program, used by over 20,000
certificated suppliers in 90 countries, with certification
issued through a worldwide network of accredited
Certification Bodies.
The Standard guarantees the standardisation of
quality, safety and operational criteria, ensures
that food manufactures fulfil their legal obligations
and provide protection for the end consumer. The
BRC Global Standards is now often a fundamental
requirement of leading food retailers.
Since the issue of BRC Global Standard version 6
(BRC, 2011), many food manufacturers have asked
whether the new standard includes the requirement
to use metal detectable products, e.g. utensils,
cleaning equipment etc.., in the food production area.
The BRC have confirmed that there is nothing in the
Standard, or the supporting interpretation guideline,
that states that equipment shall be metal detectable.
With specific regard to cleaning equipment section
4.11.5 of BRCv6 states:
4.11.5 Cleaning equipment shall be:
• fit for purpose
•suitably identified for intended use, e.g. colour
coded or labelled
• cleaned and stored in a hygienic manner to prevent
contamination
• equipment used for cleaning in high-care and highrisk areas shall be dedicated for use in that area
What BRCv6 does say, and which is new in terms of
the emphasis and extent of advice provided is that,
to comply with the BRCv6 standard, Manufacturing
operations will need to have in place much more
formal evaluations and descriptions of their pre­
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requisite programmes. Amongst the areas that may
need to be evaluated, if there are significant, specific
hazards are:
• facility design and lay-out
• low-risk/high-risk segregation
• services/utilities (water, ice, steam, gases,
compressed air)
•equipment
•maintenance
• cleaning and disinfection (including cleaning-inplace)
• personnel hygiene
• foreign bodies (plastic, metal, glass etc)
• pest control
• allergen issues
• waste disposal
Food manufacturers, who have BRCv6 accreditation
and who use metal detectable plastics and metal
detection systems, may be under the impression that
this forms part of the BRCv6 requirement for foreign
body control. It does not. The requirement is
i) to have a documented risk assessment associated
with foreign body control,
ii) that, if a significant foreign body hazard is identified
through the risk assessment process, effective
controls are in place, and that details of this control
procedure, and of its effectiveness is validated (i.e.
to show that it actually works), verified/monitored
(e.g. checked daily to make sure it still work), and
recorded.
Some food manufacturers may include the use of
metal detectable plastic equipment in their foreign
body control procedure and, therefore, this may have
been taken into account by BRCv6 auditors as part
of their overall assessment of foreign body control in
compliance with the BRCv6 Standard. However, it is
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W h i t e Pap e r
the food manufacturer that has made the decision to
use metal detectable equipment, based on their risk
assessment, and not because it is a requirement of
BRCv6.
It is also possible that food manufacturers are getting
confused between what the BRCv6 Standard requires
and what retail auditors require, as retail standards
tend to be more prescriptive and demanding.
References
Lock, A., 1990. The Guide To Reducing Metal Contamination
In The Food Processing Industry. Safeline Metal Detection
Ltd.
Deb Smith,
Global R&D Manager, Vikan
The British Retail Consortium., 2011. BRC Global standard
for food safety: Issue 6. TSO (The Stationery Office)
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