Class 7 is the exception in the IMDG Code. Every other class with a graded hazard sorts its entries into Packing Group I, II or III. Radioactive material does not. A shipper describes a Class 7 consignment by the design type of the package, the activity inside it measured against the A1 and A2 values for that radionuclide, the radiation level at the package surface and at one metre, and, where fissile material is present, a criticality safety index. Get the package type right and the rest of the regulatory chain follows. Get it wrong and no amount of correct paperwork rescues the consignment.
The sea leg carries a second layer the other classes do not have. For ordinary Class 7 cargo the IMDG Code governs. Above defined activity thresholds, the INF Code takes over and regulates the ship, not just the package: damage stability, cargo-space cooling, fire protection and a shipboard radiological emergency plan. The imdg-class-7-radioactive calculator on this site works the package-level path. The ship-level path is a certification question settled long before the box reaches the terminal.
What the class covers
Radioactive material, for transport purposes, is material whose activity concentration and total consignment activity both exceed the exemption values set out in the IAEA transport regulations. Both conditions must be met. A large mass of very slightly active material can fall outside the class because the concentration is below the threshold, and a tiny quantity of an intensely active nuclide can fall outside because the total activity is below it. This dual test is why “is it radioactive?” is the wrong question at a booking desk. The right question is whether the material exceeds both exemption values for the specific radionuclides present.
The consequence is practical. Naturally occurring radioactive material moves in bulk every day as mineral sands, fertiliser feedstock and some refractory ores, and most of it is not Class 7 because the activity concentration sits under the threshold. The same cargo from a different deposit can cross it.
A1 and A2, the activity limits that size the package
Every radionuclide has two tabulated activity values, A1 and A2, expressed in terabecquerels. A1 applies to material in special form, meaning either an indispersible solid or a sealed capsule that has passed defined impact, percussion, bending and heat tests. A2 applies to everything else. The distinction is about dispersibility rather than intensity: a sealed source that cannot spread its contents is permitted more activity than the same nuclide as a loose powder.
These two numbers do most of the work in the classification. They set the ceiling for a Type A package, they feed the calculation for mixtures of nuclides, and they determine at what point a consignment steps up to a Type B design. For a mixture, the contributions are summed as fractions of each nuclide’s limit rather than compared individually, so a package holding several nuclides each individually well under its own limit can still exceed the aggregate.
Package design types
The package is the primary safety system in radioactive transport. Unlike a Class 3 flammable liquid, where the ship’s stowage and segregation carry much of the risk control, a Class 7 consignment is engineered to contain its own hazard through the accidents the regulations anticipate.
Excepted packages carry activity so low that the radiological risk in transport is negligible. They are exempt from most marking, labelling and documentation, though the UN number still appears on the outside and the consignment remains subject to the general provisions. Instruments and manufactured articles containing small sealed sources move this way routinely.
Industrial packages, designated IP-1, IP-2 and IP-3 in ascending order of robustness, carry low specific activity material and surface contaminated objects. They are not designed against the full accident sequence. They are designed on the reasoning that the contents are too dilute or too fixed for a release to matter much, so the packaging need only prevent loss and dispersal under normal handling.
Type A packages are the workhorse. They carry up to the A1 or A2 value and must withstand normal conditions of transport: routine handling, stacking, a water spray, a free drop, a compression test and a penetration test. They are not required to survive a serious accident, and the regulatory logic accepts that, because the activity ceiling limits the consequence if one is destroyed. Medical radioisotopes, industrial radiography sources and most research quantities move in Type A.
Type B packages, subdivided into Type B(U) for unilateral approval and Type B(M) for multilateral approval, carry activity above the Type A ceiling. The design must survive accident conditions: a nine-metre drop onto an unyielding surface, a one-metre drop onto a punch bar, a fully engulfing fire at 800 degrees Celsius for thirty minutes, and immersion. These are the heavy casks used for spent fuel and high-activity sources, and a loaded one is measured in tonnes rather than kilograms.
Type C packages sit above Type B and are intended for high-activity material moving by air, where the accident energies are greater. They appear in maritime practice mainly as part of a multimodal journey.
Low specific activity material and surface contaminated objects
Two categories exist because the hazard is diffuse rather than concentrated, and forcing them into the ordinary package hierarchy would be disproportionate.
Low specific activity material, LSA, is divided into LSA-I, LSA-II and LSA-III by increasing specific activity and decreasing leachability. LSA-I covers ores and concentrates of uranium and thorium and unirradiated natural or depleted uranium. LSA-II and LSA-III cover progressively more active materials, with LSA-III requiring the activity to be essentially uniformly distributed in a relatively insoluble solid binding matrix, so that even a breached package does not release a concentrated inventory.
Surface contaminated objects, SCO, are solid objects that are not themselves radioactive but carry contamination on their surfaces. SCO-I and SCO-II are distinguished by contamination levels, with SCO-III added in the 2018 revision of the IAEA regulations for large objects that cannot practicably be transported in a package. Decommissioning waste, contaminated plant components and retired equipment from nuclear facilities move under these entries.
Non-fixed contamination on the external surface of any Class 7 package is limited to 4 becquerels per square centimetre for beta and gamma emitters and low toxicity alpha emitters, and 0.4 becquerels per square centimetre for all other alpha emitters. The limits apply on presentation for transport and are checked by wipe test. A package that fails is not a documentation problem; it is a contaminated package and the terminal will refuse it.
Transport index and criticality safety index
The transport index is the external radiation control number. Measure the maximum radiation level at one metre from the package surface in millisieverts per hour, multiply by 100, round up to one decimal place. A package reading 0.004 mSv/h at one metre has a transport index of 0.4.
The figure is not a hazard rating so much as an allocation unit. It governs which category label the package carries, how many packages may be stowed in one place, and how far the stow must sit from accommodation spaces and from undeveloped photographic film. The photographic film criterion surprises people who have not worked the class, but it is a genuine commercial constraint: fogged film is a claim, and the segregation tables treat it as a distinct exposure target with its own distances.
The criticality safety index performs the same allocation role for fissile material, controlling the accumulation of packages so that a criticality event cannot occur even if packages are damaged and rearranged. It is derived from the number of packages permitted together under defined assumptions, and the sum of criticality safety indices in any stow is capped.
Category labels
Three labels exist, and the boundaries are fixed by both the surface reading and the transport index.
| Category | Maximum surface level | Transport index |
|---|---|---|
| I-WHITE | 0.005 mSv/h | 0 |
| II-YELLOW | above 0.005 up to 0.5 mSv/h | above 0 up to 1 |
| III-YELLOW | above 0.5 mSv/h | above 1 |
A package qualifies for the lower category only if it satisfies both columns. A low transport index with a high surface reading does not buy a I-WHITE label. The category drives shipboard handling, so the labelling decision made at the consignor’s premises determines how the terminal and the ship treat the box days later.
Stowage and segregation aboard ship
Class 7 segregation departs from the familiar pattern. For most classes the segregation table returns one of four instructions based on the class pair. For radioactive material the controlling constraint is usually distance from people and from film, calculated from the aggregate transport index of the stow rather than read from a table of class pairs.
That changes the planning problem. A stowage plan that is compliant for twenty Class 3 containers is compliant regardless of how the drums inside are filled. A Class 7 stow depends on the sum of the transport indices, so two containers with identical UN numbers and identical gross weights can require different separation distances. The cargo plan has to carry the radiological data, not just the class.
Segregation from other dangerous goods still applies where the material presents a subsidiary hazard, which is common. Uranium hexafluoride is the clearest case: it is Class 7 and also corrosive and toxic on contact with moisture, and the segregation obligations of the subsidiary risk run alongside the radiological controls. UN2977 covers the fissile entry and UN2978 the non-fissile.
The INF Code and SOLAS Chapter VII Part D
Above defined activity thresholds the regulatory object changes from the package to the ship. The INF Code, mandatory through SOLAS Chapter VII Part D, applies to ships carrying packaged irradiated nuclear fuel, plutonium and high-level radioactive wastes.
Ships are certified in three classes by the total activity they may carry, INF 1 through INF 3, with requirements tightening across the range. The code reaches into damage stability, fire protection of cargo spaces, temperature control, electrical supply arrangements, radiological protection equipment and shipboard emergency planning. A ship cannot accept INF cargo because the paperwork is in order; it must hold the certificate, and the certificate follows survey against the structural and systems requirements.
This is why the sea leg of a spent-fuel movement is planned around vessel availability rather than around slot availability. The number of certified INF 3 ships in the world is small, and charter arrangements are made far in advance.
Documentation
The dangerous goods transport document for Class 7 carries elements that no other class requires. Alongside the UN number, proper shipping name and class, it states the name or symbol of each radionuclide, a description of the physical and chemical form or a statement that the material is special form or low dispersible, the maximum activity of the contents in becquerels with the appropriate SI prefix, the category label, the transport index, and the criticality safety index where fissile material is present.
Competent authority approval certificates travel with consignments that need them, which includes Type B(M) packages, many fissile packages and shipments under special arrangement. The absence of a certificate that should be present stops the consignment at the terminal gate.
Regulatory basis and currency
The maritime rules are in the IMDG Code, which gives effect to SOLAS Chapter VII for packaged dangerous goods. The IMDG Code does not independently invent the radioactive provisions; it adopts the IAEA transport regulations, which are the technical source for activity limits, package design types and testing.
The currency point matters and is easy to get wrong. The IAEA regulations are issued as Specific Safety Requirements No. SSR-6. The 2018 Edition is SSR-6 (Rev. 1), and it is the edition cited in the sources below. That document has since been superseded by SSR-6 (Rev. 2). Anyone working a live consignment should confirm which revision their national competent authority has adopted and which edition of the IMDG Code is in force for the voyage, because the IMDG Code adopts an IAEA edition on its own amendment cycle and the two can be a revision apart during a transition.
Limitations
This article describes the framework rather than the tabulated values. It does not reproduce the A1 and A2 tables, the exemption values, or the full segregation distance tables, all of which are extensive and edition-specific, and none of which should be worked from a secondary source.
It does not cover transport of radioactive material by air or road, where package requirements overlap but operational rules differ. It does not address the physical protection and security provisions that apply to nuclear material, which sit in a separate legal instrument from the transport safety regulations and are handled by different people in most organisations.
It does not address national variations. Competent authorities differ on approval routes, on notification requirements and on the timing of adoption of new IAEA revisions, and several major flag and coastal states impose additional conditions on radioactive cargo in their waters and ports.
Finally, no part of this article is a substitute for the advice of a radiation protection adviser or a dangerous goods safety adviser. Class 7 is the one IMDG class where the classification decision routinely requires measurement by a qualified person rather than reference to a data sheet.
Related calculators
- IMDG Class 7, Radioactive Shipping: the package-level path for this class, from UN entry to category label
- IMDG Segregation: segregation requirements between class pairs where a subsidiary hazard applies
- IMDG EmS Lookup: emergency schedules for the fire and spillage response
- UN2912, Radioactive material, LSA-I: the low specific activity entry described above
- UN2977, Radioactive material, uranium hexafluoride, fissile: the fissile uranium hexafluoride entry
- Container IMDG Class Lookup: class identification from a container’s declared contents
- MARPOL Annex III Marine Pollutant Lookup: whether a given entry carries the marine pollutant mark
See also
- IMDG Class 1: Explosives
- IMDG Class 2: Gases
- IMDG Class 3: Flammable Liquids
- IMDG Class 4: Flammable Solids
- IMDG Class 5: Oxidisers and Organic Peroxides
- IMDG Class 6: Toxic and Infectious Substances
- IMDG Class 8: Corrosive Substances
- IMDG Class 9: Miscellaneous Dangerous Goods
- IMDG Marking, Labelling and Placarding
- SOLAS Chapter VII: Carriage of Dangerous Goods
- MARPOL Annex III