What size foreign object is dangerous in food?

FDA's Compliance Policy Guide 555.425 treats a hard or sharp object measuring 7 mm to 25 mm in ready-to-eat food as a basis for considering the food adulterated. Objects under 7 mm rarely cause injury except in special-risk groups such as infants, the elderly, and surgery patients. Above 25 mm, objects are usually caught before swallowing but can still injure the mouth.

What are the most common physical hazards in food?

Metal is the most common and most detectable, from equipment wear, blades, and fasteners. Others are glass (lights, gauges, containers), hard plastic (totes, guards, scoops), stone (field debris in crops), bone (meat and fish processing), and wood (pallets and crates). Detectability tracks density: dense objects show on the right detector, while low-density plastic and wood lean on prevention.

Are bones and shells considered physical hazards?

It depends on the product. FDA judges hard or sharp natural components, bone in a bone-in fish cut, shell fragments in nut products, differently from foreign objects, because a reasonable consumer is aware they are intrinsic to that food. In a boneless or shelled product, though, the same fragment can be a hazard, and the hazard analysis has to reflect what the consumer expects.

How are physical hazards controlled in a food plant?

By layering complementary controls, because no single technology catches every material. Sieves and screens remove oversized debris and stones, magnets pull ferrous metal, metal detectors find a wider range of metals, and X-ray catches dense materials like glass and bone. Prevention, equipment inspection, tool control, a glass register, and supplier controls, is the cheaper half that shrinks what detectors must catch.

Where in a HACCP plan are physical hazards addressed?

In the hazard analysis, alongside biological and chemical hazards. Where a physical hazard is reasonably likely to occur, the detection step, often a metal detector or X-ray on finished product, is usually a critical control point or preventive control, with a critical limit such as detector sensitivity, monitoring, corrective actions, and verification through routine test-piece checks under 21 CFR Part 117 Subpart C.

Physical Hazards in Food

Q: What is a physical hazard in food?

A physical hazard is any hard or sharp foreign object in food, metal, glass, hard plastic, stone, bone, or wood, present at a size that can injure the person who eats it through laceration, choking, or dental damage. It is one of the three hazard classes, alongside biological and chemical, that a food safety plan must evaluate in its hazard analysis.

Q: What is the difference between a physical hazard and a foreign material control program?

A physical hazard is the category of dangerous foreign objects, metal, glass, plastic, stone, bone, wood, that can injure a consumer. A foreign material control program is the operational system a plant runs to prevent, detect, and respond to them, with device checks, glass registers, and critical control points. The hazard is the risk; the program is how the plant manages it.

A shard of metal is the one food safety failure a customer needs no lab to confirm, they feel it. This is the hazard category itself: what the objects are, how big is dangerous, and where they come from.

A physical hazard in food is any hard or sharp foreign object, metal, glass, hard plastic, stone, bone, or wood, present at a size that can injure the person who eats it, through laceration, choking, or dental damage. It is one of the three hazard classes, alongside biological and chemical, that a food safety plan must address.

Physical hazards are the most visible way a plant fails, because the person who bites a metal fragment needs no laboratory to know something went wrong. This guide covers the hazard category itself: what physical hazards are, the main types, the FDA size and injury thresholds that decide when an object makes food adulterated, where these objects come from, and the layered controls that catch them. It is the companion to the program that manages them day to day, a foreign material control program is the operational system; this is the hazard it exists to control.

What is a physical hazard in food?

A physical hazard is a foreign object or extraneous material in food capable of causing illness or injury. The key word is injury: unlike a pathogen that makes people sick over hours or days, a physical hazard hurts on contact, a cut lip, a cracked tooth, a choking risk, or a perforation somewhere along the digestive tract. Because the harm is mechanical, size and shape matter as much as the material, and a small soft fragment is a very different risk from a small hard shard.

It helps to separate two ideas that often get blurred. Physical hazards are the category of dangerous foreign objects, the subject of this guide. A foreign material control program is the operational system a plant runs to prevent, detect, and respond to them, with device checks, glass registers, and CCPs. Understanding the hazard category is what lets you build the program correctly: you cannot decide where to place a metal detector until you know what physical hazards are reasonably likely in your process and how large they would have to be to hurt someone.

The physical-hazard families and where each typically originates. Material dictates detectability: metal detectors and X-ray see metal, X-ray sees glass and stone, but low-density plastic and wood evade both.

What are the main types of physical hazards?

Six materials account for most physical-hazard events, and each behaves differently in the plant and in the body:

Metal the most common and most detectable. It comes from equipment wear, broken blades and screens, fasteners, and metal shavings. Detectable by magnets, metal detectors, and X-ray.
Glass from lights, gauges, thermometers, and glass containers. Sharp and dangerous, hard to detect except by X-ray, which is why glass is controlled mainly by prevention and a glass register.
Hard plastic from totes, machine guards, scoops, and pen caps. Brittle plastic that shatters into rigid fragments is the concern; low-density plastic is nearly invisible to detectors.
Stone field debris riding in with grains, pulses, and produce. Dense enough for X-ray to catch, removable by sieves and destoners.
Bone in meat, poultry, and fish, from processing. A natural component in some products, a hazard in others. X-ray detectable; bone-in expectations vary by product.
Wood splinters from pallets, crates, and old dunnage. Low density, hard to detect, controlled mostly by inspection and pallet policy.

The pattern to notice: detectability tracks density. Metal, glass, stone, and bone are dense and show up on the right detector. Plastic and wood are low-density and slip past both metal detection and X-ray, so they lean on prevention. That is why no plant relies on a single machine.

What size physical hazard is dangerous?

FDA put a number on it. Compliance Policy Guide 555.425 treats a food containing a hard or sharp foreign object that measures 7 mm to 25 mm in length as a basis for considering it adulterated, when the food is ready-to-eat or needs only minimal preparation that would not remove the object. Below 7 mm, the guidance notes, foreign objects rarely cause trauma or serious injury, except in special-risk groups like infants, the elderly, and surgery patients, where even smaller objects can harm. Above 25 mm, an object is generally caught before it is swallowed but can still injure the mouth.

Two caveats keep this from being a simple ruler. First, the special-risk exception matters: a product for infants or hospitals carries a lower effective threshold because the eater is more vulnerable. Second, natural components are treated differently, a bone in a bone-in cut of fish, or shell fragments in a nut product, are not adulteration in the same way, because a reasonable consumer expects and is aware of them. The 7-to-25 mm window is the anchor, but risk always depends on the object, the product, and who eats it.

FDA's CPG 555.425 thresholds. The 7-to-25 mm window is the anchor for hard or sharp objects in ready-to-eat food; special-risk groups lower the threshold, and natural components are judged differently.

Where do physical hazards come from?

Physical hazards enter from four broad sources, and naming them is the first control. First, incoming ingredients and packaging: stones in grain, bone in meat, metal in bulk powders, staples and plastic from packaging. Second, the plant and its equipment: metal shavings from wear, broken screen wire, bearing fragments, flaking paint, and glass from lights and gauges. Third, maintenance and tools: dropped fasteners, blade fragments, wire, and the occasional tool left behind. Fourth, people: jewelry, pen caps, buttons, and personal items, which is why personnel hygiene rules on jewelry and personal effects are also physical-hazard controls.

Each source maps to a control. Incoming material is managed by supplier approval and receiving inspection; equipment by inspection and maintenance; tools by tool control and reconciliation; people by GMPs. Tracing your own likely sources is more valuable than buying detectors and hoping, because prevention at the source shrinks what any detector has to catch.

What controls keep physical hazards out?

Because detectability varies by material, plants stack complementary controls rather than trusting one. The layers, from raw material to finished pack:

Control	Catches	Main limitation
Sieves & screens	Oversized debris, stones, agglomerates	Only material larger than the mesh; must stay intact
Magnets	Ferrous metal in flowing bulk product	Ferrous metals only; needs cleaning and strength checks
Metal detectors	Ferrous, non-ferrous, and stainless metal	Product effect masks small metal; struggles with foil
X-ray inspection	Dense materials: metal, glass, stone, bone	Weak on low-density plastic, wood, hair; higher cost
Vision & prevention	Surface objects; glass and plastic by register and policy	Surface only; prevention depends on discipline

No single control catches every physical hazard. Programs layer them, a magnet and sieve on raw material, a metal detector or X-ray on finished product, so the classes one misses are covered by another.

The controls above are the detection half; prevention is the other and cheaper half, equipment inspection, tool control, a glass and brittle-plastic register, and supplier controls that stop objects before they reach a detector. Assembled and run day to day, these prevention and detection layers plus a response plan are what a foreign material control program coordinates. This guide is about the hazard; that program is how a plant manages it on the floor.

How do physical hazards fit the food safety plan?

Physical hazards are assessed in the hazard analysis of a HACCP or food safety plan alongside biological and chemical ones, and the analysis decides how each is controlled. Run it as a repeatable sequence:

Identify the physical hazards. For each ingredient and process step, list the hard or sharp objects reasonably likely to occur, by material and likely source.
Judge severity and likelihood. Weigh the object's potential to injure (size, sharpness, hardness) against how likely it is to reach the consumer, factoring in special-risk consumers.
Compare to the threshold. Use FDA's 7-to-25 mm window and the special-risk exception to decide whether a given hazard rises to an adulteration concern.
Assign a control. Route each hazard to prevention (supplier, tool, glass control) or detection (sieve, magnet, metal detector, X-ray), and decide whether the detection step is a preventive control or critical control point.
Set limits and monitoring. Where a step is a CCP, define the critical limit, detector sensitivity, test-piece size, and monitor it with documented performance checks.
Verify and reassess. Confirm detectors work with routine test pieces, review reject and complaint trends, and revisit the analysis when equipment, ingredients, or products change.

Where a physical hazard is reasonably likely, the detection step, commonly the metal detector or X-ray on finished product, is usually a critical control point with a limit, monitoring, corrective actions, and verification. That makes routine detector checks with test pieces a compliance requirement, not a nicety.

The numbers worth pinning

Physical-hazard thresholds come from FDA guidance and rule, cite them directly:

A hard or sharp foreign object measuring 7 mm to 25 mm in ready-to-eat food is a basis for considering the food adulterated, FDA CPG 555.425.
Objects smaller than 7 mm rarely cause injury except in special-risk groups such as infants, the elderly, and surgery patients (same guidance).
Hard or sharp natural components bone in fish, shell in nuts, are judged differently, because a consumer is aware they are intrinsic to the food (same guidance).
Physical hazards must be evaluated in the hazard analysis under 21 CFR Part 117 Subpart C where a validated detection step is often a preventive control or CCP.

The proof that these controls run lives in records, detector test-piece checks, glass-register inspections, tool reconciliations, and reject investigations. Paper makes those easy to skip and hard to retrieve; capturing them at the point of work flags a missed detector check in real time and turns audit prep into a query. It is the digitize-the-paper move Harmony runs for production and quality logs (see how CLS did it), and it ties physical-hazard control to GMP compliance and the SSOPs that keep glass and equipment in check. For the pet-food angle on the same hazards, see pet food safety and for the plant-wide preventive framework, preventive controls for human food.