Summary
In short
- X-ray detects by density. It finds glass, stone, bone and dense plastic that metal detection misses, and it misses low-density material that people assume it catches.
- Wood is a common and consequential blind spot. It caused one of the largest US recalls of 2025 by weight, and it is poorly detected by x-ray because its density is close to many foods.
- The system is also a cabinet x-ray system under 21 CFR 1020.40, with an emission limit of 0.5 milliroentgen per hour at five centimetres from the external surface, plus required interlocks, indicator lights and warning labels.
- Most US states require the owner to register the equipment with the state radiation control programme, and this obligation sits with the site rather than the manufacturer.
- Test piece frequency is a commercial decision about how much product a failed check puts on hold, because everything since the last successful check is suspect.
- Sensitivity is product-specific. A validated sensitivity for one product does not transfer to another with different density, depth or packaging.
What it is
What it is
What is an x-ray inspection check?
Routine verification that the x-ray system is detecting to its validated sensitivity, performed with certified test pieces of defined material and size passed through the system in representative product, with the reject function confirmed and the result recorded.
What does x-ray detect that metal detection does not?
X-ray discriminates by density, so it detects glass, stone, bone, dense plastics, rubber and ceramic that metal detection cannot see. It also handles metallised film and foil packaging that defeats metal detection. What it does not reliably detect are low-density materials: most soft plastics, wood, cardboard, hair, paper and insects.
When to use it
When to use it, and when not to
This check verifies detection performance. The radiation safety obligations run alongside it and are frequently held nowhere.
Use it for
- Routine verification of detection sensitivity with certified test pieces at defined frequency
- Start of run, after any stoppage, at product changeover and at run end
- After maintenance, adjustment or software change to the system
- When a new product is introduced, requiring its own sensitivity validation
- Following a foreign material finding that the system should have detected
Not for
- Sensitivity validation, which establishes the achievable detection level per product and is performed on introduction and change
- The radiation survey and state registration, which are radiation safety obligations rather than food safety ones
- Operator radiation safety training, which is a separate requirement with its own record
- The foreign material report, which records an actual finding and its investigation
- Metal detection verification, which is a different technology with different capabilities and its own record
Standards
What it is built against
X-ray inspection sits under food safety scheme requirements for detection and under a federal radiation performance standard for the equipment itself.
| Clause | Requirement | Where it lands |
|---|---|---|
| BRCGS Issue 9 cl.4.10 | Foreign body detection equipment: validation, verification with test pieces, failure procedures and records | Test pieces |
| 21 CFR 117.130 | Hazard analysis identifying physical hazards requiring a preventive control | Header |
| 21 CFR 117.145 | Monitoring of preventive controls with records signed and dated | System function |
| 21 CFR 117.150 | Corrective action where a preventive control is not properly implemented | Failure response |
| 21 CFR 1020.40 | Cabinet x-ray performance standard: 0.5 mR per hour at 5 cm, interlocks, indicator lights, warning labels | System function |
| State radiation control | Registration of the equipment by the owner with the state radiation control programme, varying by state | Header |
| SQF Edition 9 cl.11.2 | Foreign matter control including detection equipment and incident response | Failure response |
| 9 CFR 417 | Where detection is a CCP, monitoring, corrective action and verification requirements apply | Test pieces |
What it does not cover
- Sensitivity validation per product, which establishes what is achievable and is performed on introduction and on change.
- Radiation survey and state registration, which are equipment obligations distinct from food safety verification.
- Operator radiation safety training, required separately from food safety training on the same equipment.
- The foreign material report, which handles an actual finding and its source investigation.
- Metal detection verification, which covers a different technology with different blind spots.
Filling it in
Filling it in well
The check is short. What makes it meaningful is the test piece regime behind it and knowing what happens to product when it fails.
Test pieces should be certified for material and size, and passed through in product rather than through an empty system. Product effect is substantial in x-ray: density, depth, packaging and product presentation all change what is achievable, and a test through air demonstrates the machine works rather than that the inspection works.
Detection varies across the belt width and with the orientation of the object. Test pieces should be presented at the position and orientation where detection is hardest, typically the belt edges and with the piece oriented to present its smallest cross-section. Testing at the easy position produces reassurance rather than verification.
Everything produced since the last successful check is suspect if a check fails. Frequency is therefore a decision about how much product you are willing to hold, not a compliance minimum. Hourly is common; high-risk lines run more often. Decide the number explicitly rather than inheriting it.
A detection that does not result in the pack leaving the line has not protected anyone. The check should confirm the reject mechanism operated, the pack reached the reject bin, and where fitted that bin-full and air-pressure failsafes are functional. Detection without effective rejection is the failure mode that produces product in the market.
Audit findings
Common audit findings
X-ray findings divide between detection verification and the radiation obligations that frequently have no owner.
| Finding | Clause | What fixes it |
|---|---|---|
| Test pieces passed through an empty system rather than in product. | BRCGS 4.10 | Test in representative product; product effect materially changes achievable sensitivity. |
| Sensitivity validated for one product and applied to others. | BRCGS 4.10 | Validate per product; density, depth and packaging all change what is detectable. |
| Test pieces presented at the easiest position on the belt. | BRCGS 4.10 | Test at the least favourable position and orientation. |
| Reject function not confirmed as part of the check. | 21 CFR 117.145 | Confirm the pack left the line; detection without rejection protects nobody. |
| No defined hold rule when a check fails. | 21 CFR 117.150 | Define in advance what is held; deciding scope after a failure produces narrow decisions under pressure. |
| Equipment not registered with the state radiation control programme. | State regulation | Registration sits with the owner; check state requirements at installation and on relocation. |
| Interlocks, indicator lights or warning labels defeated or missing. | 21 CFR 1020.40 | These are required safety features; a defeated interlock is a radiation safety failure. |
| Operators trained on food safety use but not on radiation safety. | 21 CFR 1020.40 | Provide radiation safety training as a distinct requirement. |
| X-ray assumed to detect low-density material such as wood or soft plastic. | BRCGS 4.10 | Document detection capability by material; low-density contaminants remain a gap. |
| No verification after maintenance or software change. | BRCGS 4.10 | Reverify after any intervention; settings and calibration can change without notice. |
Worked case
Case in point: the upgrade that narrowed the net
A processor replaced metal detection with x-ray on a packing line, on the reasonable basis that x-ray detects more contaminant types and handles the metallised film they had moved to. Validation was performed with certified test pieces, verification ran hourly, records were complete, and the system performed exactly as specified.
Some months later a customer complaint identified a wood splinter from a pallet in a finished pack. The x-ray had not detected it, correctly by its own specification: wood density sits close to many food matrices, and low-density material is where x-ray is weakest. Metal detection would not have found it either.
The gap was not the equipment. It was that the change from metal detection to x-ray had been treated as an upgrade rather than as a change in detection profile, and nothing in the hazard analysis had been revisited to ask what the new system could and could not see.
Definitions
Definitions and key terms
- Product effect
- The influence of product density, depth, packaging and presentation on achievable detection sensitivity.
- Certified test piece
- A sphere or rod of stated material and diameter, traceable, used to verify detection performance.
- Least favourable position
- The location and orientation where detection is hardest, typically belt edges and smallest cross-section presentation.
- Cabinet x-ray system
- An enclosed x-ray system regulated under 21 CFR 1020.40, with required interlocks, indicators and emission limits.
- Reject confirmation
- Verification that a detected pack physically left the line and reached the reject container.
- Failsafe
- A function stopping the line or diverting product when reject air pressure fails or the reject bin is full.
- Sensitivity validation
- Establishing the smallest reliably detectable object per product, performed on introduction and on change.
- Radiation survey
- Measurement confirming emission remains within the performance standard limit at the equipment's external surfaces.
FAQ
Frequently asked questions
Does x-ray detect everything metal detection does?+
Not identically. X-ray detects by density and finds glass, stone, bone, dense plastic, rubber and ceramic that metal detection cannot see, and it works in metallised packaging that defeats metal detection. Fine low-density metals in some product presentations can be harder for x-ray than for a well-set metal detector, and low-density contaminants generally remain a gap for both.
What does x-ray miss?+
Low-density material: most soft plastics, wood, cardboard, paper, hair, string and insects. Wood is the important case because its density sits close to many food matrices and it caused one of the largest US recalls of 2025 by weight. Where these are credible hazards, the control has to be at source rather than at detection.
Do we need to register the equipment?+
In most US states, yes. An x-ray inspection system is a cabinet x-ray system under 21 CFR 1020.40, and state radiation control programmes generally require the owner to register it. The obligation sits with the site rather than the equipment supplier, and it is frequently discovered during a state inspection rather than at installation.
How often should test pieces be run?+
Frequency is a commercial decision constrained by risk, because everything produced since the last successful check is suspect when a check fails. Hourly is common and higher-risk lines run more often. The useful question is how much product you are prepared to hold, and the interval follows from that answer rather than from a scheme minimum.
Does the check cover the reject mechanism?+
It should. Detection that does not physically remove the pack has protected nobody, and reject failures are a recognised route by which detected product reaches the market. Confirm the pack reached the reject container and that failsafes for air pressure and bin-full conditions are functional.
Is a validated sensitivity transferable between products?+
No. Density, depth, packaging and presentation all affect what is achievable, so each product requires its own validation. Applying one product's sensitivity to another produces a documented figure that the system cannot deliver for the product actually running.
The agents
What the agents do with it
The check is a test piece and a signature. What fails is the reject nobody confirmed, and the radiation registration nobody owns.
Holds validated sensitivity per product, drives the test piece regime, and applies the defined hold rule automatically when a check fails.
Registers the system as an asset with its radiation obligations attached, including survey and state registration alongside routine maintenance.
Flags a change of detection technology as a management of change event, so the hazard analysis is revisited rather than assumed to improve.
Covers radiation safety training as a distinct requirement from food safety operation of the same equipment.
This template lives in KnowQuality — quality and food safety. HACCP, nonconformance, traceability, laboratory and customer complaints.
Sources
Sources
- 21 CFR 1020.40, cabinet x-ray systems performance standard, FDA
- FDA Compliance Guide for Cabinet X-Ray Systems
- BRCGS Food Safety Issue 9 clause 4.10, foreign body detection and removal
- 21 CFR 117, hazard analysis and risk-based preventive controls, FDA
- USDA FSIS 2025 recall data on foreign material