It is the IMO rulebook for dangerous goods on a ship: how to class them, pack them, mark them and stow them. Each substance gets a class, a UN number and packing rules that the carrier and the terminal have to follow.
Class 6
Toxic substances
Read the divisions below as a planning note. The class name tells you the main hazard. Packing, labels and where the box may sit on the ship still come from the IMDG Code.
Toxic and infectious substances, class 6
Division 6.1. Toxic substances
Known to be poisonous to people in a way that threatens health while the cargo is moving, or treated as poisonous because animal tests put it in a toxic category.
Also covers an irritant such as tear gas, which causes severe irritation, especially in a closed space.
Division 6.2. Infectious substances
An infectious substance is known, or reasonably expected, to contain a pathogen: a bacterium, virus, parasite, fungus, or an agent such as a prion, that can cause disease in people or animals.
A toxin from a plant, animal, or bacterium that contains no infectious substance is considered under division 6.1 and assigned to UN3172.
A culture is a pathogen grown on purpose. A patient specimen is material taken directly from a person or an animal, such as blood, tissue, or a swab, and sent for diagnosis, research, or treatment. Medical waste is waste from treating people or animals, or from biological research.
Category A can cause permanent disability, a life-threatening illness, or death in an otherwise healthy person or animal if it escapes the packaging. Disease in people, or in people and animals, is UN2814, Infectious substance, affecting humans. Disease in animals only is UN2900, Infectious substance, affecting animals only. If there is doubt, it is Category A.
Category B is an infectious substance that does not meet Category A. It is UN3373, Biological substance, category B.
These are not class 6.2 unless another class applies: material with no pathogen, a micro-organism that does not cause disease, a pathogen that has been inactivated, and an environmental sample such as food or water that is not a significant infection risk. Dried blood spots, blood collected for transfusion, and tissue or organs for transplant are also outside these rules.
A patient specimen with only a minimal chance of a pathogen may travel outside the rules if the pack cannot leak and is marked Exempt human specimen or Exempt animal specimen. The pack has a leak-proof primary receptacle, a leak-proof secondary packaging, and an outer packaging with at least one face of 100 mm by 100 mm. Liquids need enough absorbent between the two inner layers to hold the whole contents. Fragile primary receptacles in one secondary packaging are wrapped or separated so they do not touch. That judgment uses the medical history, the symptoms, and local conditions. Typical examples are tests for cholesterol, glucose, hormones, PSA, organ function, medicines, employment or insurance screening, pregnancy, a cancer biopsy, and antibody checks.
A biological product such as a vaccine that is made and packed under a national authority, and sent for final packing or for personal care, is outside these rules. If it is known or reasonably believed to contain an infectious substance, it is UN2814, UN2900, or UN3373.
A genetically modified micro-organism that is not an infectious substance is classified under subsection 3.9.
Medical waste with a Category A substance is UN2814 or UN2900. Waste with a Category B substance, or waste thought unlikely to contain an infectious substance, is UN3291. The shipping name for UN3291 is clinical waste, unspecified, n.o.s., or the equivalent medical-waste name.
A live animal that was infected on purpose must not go by air unless the substance cannot be sent any other way, and only on terms the national authority approves. A live animal is not used to carry the substance when another way exists. A carcass with a Category A pathogen is UN2814 or UN2900. A Category B carcass follows the competent authority. Other patient specimens are UN2814, UN2900, or UN3373 unless they meet the exempt-specimen pack above.
Questions
What a class does not settle
The class names the main hazard. Many goods also have a second one, such as a poisonous gas that can also burn. The papers and the placards show both, and the separation rules follow whichever hazard is stricter.
It belongs to the substance, or to a small group of similar substances, in the IMDG Dangerous Goods List. It is not one number for a whole class. Two boxes in the same class can have different numbers, packing groups and separation rules.