Class 7 in air transport: the rigorous system that makes the safe movement of radioactive materials possible

When we think about dangerous goods, we tend to picture flammable chemicals or corrosive substances. But one class demands an even higher level of rigour: Class 7, radioactive materials. Medical isotopes for cancer diagnosis and treatment, industrial calibration sources, materials for scientific research and energy production — all of them circulate daily through airports and cargo terminals around the world. What makes this possible, safely, is an international regulatory system of extraordinary complexity and precision.

The first pillar: mandatory training

Before any radioactive package is handled, packed, documented, or transported, one non-negotiable prerequisite must be in place: training. This is not an administrative formality. It is the system's first line of defence.

All personnel who come into contact with Class 7 materials — those who pack, those who sign documentation, those who load and unload, those who transport — must have received specific, certified training in the safe practices applicable to this class. A properly prepared human factor is, by some margin, the most important component of the entire system.

Classifying the risk: categories, transport index, and labelling

Once training is assured, the system requires the risk level of each consignment to be quantified and communicated. Two fundamental technical criteria are used:

 

Dose rate at surface Radiation measured directly on the outer surface of the package. The lower the value, the lower the risk of exposure from direct contact.

Transport Index (TI) A number indicating the intensity of radiation measured at one metre from the package. Used to calculate safe distances and to control the accumulation of packages.

 

Based on these values, each package is assigned to one of three categories, which determine the required controls:

 

Category	Condition	Required controls
I — WHITE	Minimal surface dose rate; TI not applicable or negligible	Standard handling. External radiation risk is practically negligible.
II — YELLOW	Moderate surface dose rate; TI ≤ 1	Mandatory segregation distances calculated from the TI.
III — YELLOW	Higher surface dose rate; TI between 1 and 10	Stricter controls, greater separation distances, specific logistical management.

 

The Transport Index is particularly relevant when several packages are grouped together: even if each package individually meets the limits, their combined presence can create a more significant radiation field. The regulations provide precise tables for calculating how many packages may be grouped and what minimum distances must be maintained from personnel and other cargo.

The packaging: IAEA-certified fortresses

The International Atomic Energy Agency (IAEA), a United Nations body, defines the radiological safety standards that govern the design and testing of Class 7 packaging. The principle is always the same: the correct packaging for the correct material, in the correct quantity.

 

IP-1, IP-2, IP-3 (Industrial) For low-activity materials. Ensure containment and integrity under normal transport conditions: vibration, stacking, rain.	Type A For higher activities than industrial packages. Designed to withstand normal transport conditions without loss of contents.
Type B (BU / BM) For high-activity materials. Tested under severe accident conditions: high-speed impacts, drops onto steel bars, fires at 800 °C for 30 minutes, and prolonged immersion in water.	Type C Exclusively for the air transport of large quantities. Exceeds Type B requirements with even more demanding impact tests, designed for the most extreme aviation accident scenarios.

 

Documentation: the thread of accountability

A perfect package is worthless if the information accompanying it is incorrect or incomplete. The Shipper's Declaration for Dangerous Goods is the central document and must record, with absolute precision:

•       Technical name of the radioactive material

•       Class 7 and the corresponding UN number

•       Total activity, expressed in becquerels (Bq) — the international unit for radioactivity

•       Physical and chemical form of the material

•       Package category (I-White, II-Yellow, III-Yellow)

•       Transport Index, where applicable

•       Exact type of packaging used

 

For Type B and Type C packages, approval certificates issued by the competent authorities of the countries involved are also required, validating that the specific packaging design has passed the IAEA-required tests.

Equally mandatory: the consignor must provide detailed emergency instructions — what to do in the event of fire, spillage, or damage to the package — and an emergency telephone number that is operational 24 hours a day, 7 days a week, throughout the entire transit.

Transport: segregation, monitoring, and inspection

Controls do not cease once the cargo leaves the point of despatch. Throughout the entire journey, strict segregation rules apply — keeping radioactive packages at calculated distances from workers, passengers, crew members, and other sensitive cargo such as unexposed photographic film or foodstuffs.

The carriage of Class 7 materials on passenger aircraft is very heavily restricted. Most higher-activity consignments travel exclusively on cargo aircraft.

Throughout the journey, radiation level measurements may be taken at terminals and transit points to verify the integrity of packages. The relevant authorities — customs, civil aviation — conduct regular inspections covering documentation, labelling, markings, the physical condition of packages, and compliance with storage and segregation requirements.

What is all this for?

Faced with such complexity, it is essential to remember the purpose of this system. Class 7 radioactive materials are indispensable for:

•       Medical diagnosis and treatment — isotopes for scintigraphy, PET scanning, radiotherapy, and brachytherapy

•       Industrial quality control — sources for the inspection of welds, pipelines, and structures

•       Nuclear energy production — transport of fuel and waste

•       Scientific and academic research

 

This entire system of extraordinary complexity exists for a single objective: to allow society to benefit from these vital technologies whilst keeping the risks under rigorous and permanent control.