Cargo X-ray inspection is a form of non-intrusive inspection (NII): the goods are imaged without unpacking them, and only consignments whose images raise questions are opened. The same physics is used everywhere, but the equipment, the rules and the people responsible differ a great deal between air cargo, ocean containers and road or rail traffic at land borders. This page is the overview; the hardware itself is described on cargo and container scanners.
Three different screening problems
| Mode | Main purpose of X-ray | Who usually screens | Typical equipment |
|---|---|---|---|
| Air cargo | Aviation security — prevent explosives and other threats from being loaded onto aircraft | Airlines, cargo handlers, regulated agents / certified screening facilities | Conventional and dual-energy tunnel X-ray for parcels and pallets; increasingly CT; ETD, canines and physical search as alternatives |
| Sea containers | Customs enforcement — undeclared or misdeclared goods, drugs, weapons, smuggled people, sanctions and revenue fraud | Customs authorities (sometimes operated by port or contractor staff) | High-energy (MeV) container scanners: fixed portals, mobile truck-mounted units, rail scanners |
| Land borders | Customs and border security for trucks, cars, buses and trains | Customs and border agencies | Drive-through portals, gantry systems, backscatter vans, rail scanners |
Air cargo screening
Air cargo is screened for security rather than for customs purposes. In the United States, the Implementing Recommendations of the 9/11 Commission Act of 2007 requires all cargo carried on passenger aircraft to be screened at a level commensurate with checked baggage, and TSA lets certified facilities in the supply chain screen cargo before it reaches the airline. In the EU, cargo must either be screened or come from a secure supply chain (regulated agents and known consignors). Approved methods include X-ray, explosive trace detection, physical search, explosive detection dogs and metal detection; not every method suits every commodity. See the dedicated page on air cargo screening rules and responsibilities.
Air cargo equipment ranges from parcel-size tunnels (similar to checkpoint machines) to large-aperture pallet systems that can take a built-up unit load device (ULD). Because pallets can be dense, mixed and large, many items are broken down to piece level for screening, or screened before they are consolidated.
Ocean container inspection
Most ocean containers are never X-rayed. Customs agencies use risk management — advance electronic manifest data, trader history, routing, commodity and intelligence — to pick a small share of containers for examination. Selected containers go through a high-energy scanner, the image is compared with the declaration, and if something does not match the container is opened (devanned) for a physical examination. In the United States, CBP also passes inbound containers through radiation portal monitors, which detect radioactive material but do not produce images.
A legal requirement to scan 100% of US-bound containers overseas was written into the 9/11 Act, but it has not been implemented in practice; the deadline has been repeatedly extended because of cost, throughput and diplomatic obstacles, and US policy relies on risk targeting and programmes such as the Container Security Initiative instead. If your own shipment has been selected, see what happens when customs X-rays your container.
Land border and vehicle inspection
At road crossings, trucks are commonly scanned with drive-through or gantry systems; some designs avoid irradiating the driver's cab, or use a lower dose for the cab section. Smaller vehicles may be imaged with backscatter systems that reveal organic material such as drugs or people behind panels. Rail scanners image whole trains as they pass at low speed.
How cargo images are reviewed
Cargo images are read by trained analysts, often remotely at a central image-review station. The analyst compares what the image shows with the declared goods: a container declared as “furniture” should show furniture-shaped objects with plausible densities, not a uniform dense block. Common indicators include:
- Density or texture that does not match the declared commodity;
- Anomalies in structural areas — false walls, modified floors, roof cavities, refrigeration units, pallet bases;
- Organic-looking masses hidden among inorganic goods (or the reverse), using the material-discrimination colours on dual-energy systems — see what X-ray image colours mean;
- Uneven loading, inconsistent quantities or voids.
Software increasingly assists the analyst: manifest-to-image comparison, automatic detection of certain objects, and image libraries of known clean loads. The decision to open a container remains a human one. Interpretation skills are discussed on X-ray image interpretation.
What X-ray cannot do well
- Very dense or very homogeneous loads (steel coils, stone, dense metal scrap, some bulk liquids) can exceed penetration or hide small items in uniform clutter.
- Chemical identity. X-ray shows shape and density, plus approximate effective atomic number on dual-energy systems. It cannot by itself tell sugar from a drug; confirmation needs sampling, trace detection or a physical exam.
- Some commodities — perishables in sealed packaging, live animals, very large or irregular items — may be impractical to X-ray and are screened by other approved means.
Radiation and goods
The radiation dose delivered to goods during a cargo scan is very small and does not make food, medicines or other goods radioactive. High-energy scanners are, however, powerful sources: they operate inside controlled exclusion zones, with shielding, interlocks and dosimetry for staff. The engineering is covered under shielding and facility layout and the regulatory side under regulations.
Frequently asked questions
What is cargo X-ray inspection?
It is non-intrusive inspection: freight, containers or vehicles are imaged with X-rays so that officers can compare what is inside with what was declared, and only open the consignments whose images raise questions.
Are all shipping containers X-rayed?
No. Customs authorities select a small proportion of containers using risk-targeting based on advance data. The rest are released without a scan.
Who screens air cargo?
Responsibility rests with the aircraft operator under the national security programme, but screening is often done earlier in the supply chain by certified or regulated parties (for example TSA-certified cargo screening facilities in the US or regulated agents in the EU).
Can X-ray identify drugs or explosives in cargo?
X-ray reveals shapes, densities and an approximate material class, which is enough to flag anomalies. Confirming what a substance actually is requires trace detection, sampling or a physical examination.
Sources
- TSA — Cargo programs and the Certified Cargo Screening Program
- Federal Register — Air Cargo Screening interim final rule (2009)
- U.S. GAO-10-12 — Feasibility of scanning 100 percent of US-bound containers
- CBP — Container Security Initiative
- World Customs Organization — SAFE Framework of Standards
Last reviewed on 2026-10-04.