Foreign Object Detection: Retailer Codes of Practice Compliance

To ensure a maximum level of food safety for their customers, top retailers have established codes of practice or requirements with regard to the prevention and detection of foreign objects. Generally, these are improved versions of the standards that were established by the British Retail Consortium several years ago.

Marks and Spencer (M&S), a top retailer in the United Kingdom,  has developed one of the most rigorous food safety standards. Other leading retailers are following suit.

M&S standards stipulate the kind of foreign object detection system that should be utilized, how the system should 'fail' safely under all kinds of conditions, how it should work to make sure that the rejected products are eliminated from production, what records must be kept, how the system should be audited and what the required sensitivity is for different sizes of metal detector apertures, among others.

The standard also stipulates when an X-ray inspection system should be utilized rather than a metal detector.

The purpose behind this background information is to explain the M&S needs, so that food manufacturers who deliver packaged food products to retailers with these or similar requirements can completely understand the kinds of options, features and performance needs of the inspection and detection systems.

By fulfilling this 'gold standard,' food manufacturers can be assured that their product inspection program will provide the confidence that is increasingly insisted upon by leading retailers for consumers’ safety. Such an inspection program also provides the best possible protection to food manufacturers’ brands.

To address the rising trend among retailers to meet these stringent requirements, Thermo Fisher Scientific has now developed the Thermo Scientific™ Sentinel™ Multiscan Metal Detector for conveyor systems in addition to Thermo Scientific™ APEX metal detectors for drop-through and pipeline systems, and Thermo Scientific™ NextGuard™ X-ray Inspection Systems to fulfill these rigorous needs.

Figure 1. Image Credit: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

Basic Conveyor System Compliance Features

M&S specifies the following system features to fulfill its core requirements. It should be noted that all these items come as standard in the Thermo Scientific™ M&S-compliant systems.

• All sensors in the system should be failsafe so that in the event of their failure, they can remain in the closed position and activate an alarm
• Pack registration photo eye on the infeed
• Automatic rejection system (such as belt stop)
• Complete enclosure between the reject bin and the inspection point to prevent the removal of a contaminated product
• Lockable reject bin
• Bin open and unlocked time alarm
• Bin full notification
• Reject confirmation sensing (reject activation for retracting the belt systems)
• Key switch to start the line
• Low air pressure switch with air dump valve
• Lamp stack with:
  • Alarm horn
  • Red lamp, in which blinking indicates bin open and on/steady indicates alarms
  • The white lamp indicates the necessity for QA Check (audit software feature)

For applications requiring a higher level of compliance, systems must include the following additional features. Such items are supported but are optional on the Thermo Scientific M&S-compliant systems.

• Speed encoder
• Exit check sensor

The following diagram of an APEX metal detector depicts the features explained in the previous sections.

The latest-technology Sentinel multiscan metal detector would further increase sensitivity and improve the probability of detection. It is well-suited to  applications that have high product effect (for example, fresh fruits and vegetables, bakery confectionery, dairy and meat).

Figure 2. Image Credit: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

APEX Metal Detector Compliant System Features

Failsafe Operation Details

Failsafe fault and alarm notification features are standard in all M&S-compliant systems:

• Fault and alarm notifications (through the light stack and on-screen)
• Reject bin open and unlocked alarm
• Reject bin full alarm
• Reject confirmation alarm
• Metal detector fault
• Exit Check pack detection for higher-level compliance (optional)
• Reject device failure alarm for retracting conveyor belt systems only
• Air pressure failure alarm for standard pusher and air blast rejection

All alarms and faults should persist following a power cycle. Only a QA manager or an authorized user who has a key switch can clear these faults and alarms and resume the line. 

Testing Protocols Supported

All standard Thermo Scientific systems that comply with M&S requirements can perform the following rejection-related tests, ensuring system integrity. 

• Reject Confirmation Test
  • A key switch is used for this test
  • Turning the key switch to the 'Test' position disconnects the electrical supply to the reject solenoid
  • Next, a test pack with a contaminant can be passed down the line
  • The inspection system should detect the contaminant and generate a reject signal
  • With the supply to the reject valve disconnected, the reject device should not operate
  • The system should identify that the reject did not enter the bin, trigger an alarm and halt the conveyor belt
• Bin Full Test
  • The system should be able to determine that the bin is full, trigger an alarm and halt the conveyor belt
  • A mechanical device set up in the reject bin breaks the beam of the Bin Full photo-eye, simulating that the bin is full

Special Considerations for Belt Stop and Retracting Belt Rejection

Belt Stop systems will comprise an audible and/or visible reject indicator as well as a key-switch to resume activity. If more than one pack is being checked across the belt width or products are arbitrarily placed on the conveyor in bulk mode, then a retracting belt system should be utilized.

Periodic Auditing Capability

All Thermo Scientific X-ray systems and metal detectors include software to automate the auditing procedure during production. The system will alert operators when to audit and remind them to pass through the system challenge products containing foreign objects.

In the case of APEX metal detectors, this is called a Quality Audit Test (QAT).  For  NextGuard X-ray systems and Sentinel metal detectors, it is referred to as QA Check.

Reports stored on the system record when an audit is done and whether it was a pass or fail. The M&S audit standard specifies that test products should be run in three positions: leading edge, center and trailing edge. For efficiency, QA check can be set up to run all three at once. 

Figure 3. Image Credit: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

QA Check Capability with the Sentinel Metal Detector

Sensitivity Guidelines

The following table shows the sensitivity needed to conform to the M&S guidelines.

Table 1. Metal Detection Sensitivity Requirements. Source: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

Level 1 Sensitivity —  This is the target range of test piece sizes that should be detectable based on the height of the product on the conveyor and the use of a suitably sized metal detector. This should afford the best sensitivity for every food product.

Level 2 Sensitivity — This is used when  there is documented proof that test piece sizes within the range of Level 1 Sensitivity can't be achieved because of high product effect or packaging with metalized film. 

For metal detection in the Level 2 Sensitivity range, the Sentinel metal detector is preferred as its flexibility, increased sensitivity and improved probability of detection will provide the best results.

When to Use an X-Ray Inspection System

While metal detectors can be employed at low frequency with products that have metals in their packaging, in general the sensitivity will be much better with X-ray inspection. This applies to packaged products with  metalized film, metal jars and cans with metal lids and aluminum foil trays.

 X-ray technology may also be able to identify foreign objects, such as stone, bone, or glass. The NextGuard X-ray system includes the capabilities to meet the needs of retailers, such as M&S, in these cases.

Figure 4. Thermo Scientific™ NextGuard™ Pro X-ray Inspection System (not shown with complete M&S capability). Image Credit: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

Figure 5. Image Credit: Thermo Fisher Scientific – Solutions for Industrial and Safety Applications

Conclusion

X-ray systems and metal detectors have been adopted across the world for more than seven decades to protect both consumers and brands from foreign objects.

Users can develop a false sense of security, however, if the system they selected cannot react correctly to every conceivable failure mode. This could result in escapes of contaminated product.

M&S and other similar retailer standards were established to ensure a complete system design that is safe under all conditions, tackling the all-too-common shortcomings of less robust systems.

M&S compliance sets a best practice standard for food safety inspection emulated by food companies around the world. These standards are fully supported by Thermo Fisher Scientific because the company’s mission is to make the world a healthier, cleaner and safer place.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Solutions for Industrial and Safety Applications.

For more information on this source, please visit Thermo Fisher Scientific – Solutions for Industrial and Safety Applications.