The consignor is required to determine the classification of a dangerous substance before allowing a carrier to take possession of it. The consignor must ascertain whether the shipping name of the dangerous substance in question is included on the lists of products found in the TDGR.

The lists provide not only the shipping name but also the primary class, the explosives compatibility group, the subsidiary class (as the case may be), the UN number, the packing group, the transportation requirements, and specific provisions to be adopted.

When the dangerous substance is not on the list of products and tests have revealed that it does not satisfy the criteria pertaining to a given class, the dangerous substance is not subject to the TGDR.

A consignor may use a classification that was determined by (a) for Class 1, Explosives, the Chief Inspector of Explosives, Department of Natural Resources; and (b) for Class 6.2, Infectious Substances, the Director, Office of Biosafety, Health Canada, or the Director, Biohazard Containment and Safety, Canadian Food Inspection Agency; a previous consignor of the dangerous goods; or the manufacturer.

It is strongly recommended that carriers ensure that the shipper has classified dangerous substances before accepting them. If they have not been classified, or if an error is noticed, the carrier should notify the shipper.

Dangerous substances are divided into nine classes according to the risk they pose to public safety. Most classes are subdivided according to the characteristics of a given substance.