Which hazard classes require placarding at any quantity?

Table 1 of the Hazardous Materials Table lists hazards so dangerous that any amount triggers full placarding requirements. These include explosives classes 1.1, 1.2, and 1.3 (mass-detonation hazards); poison gas (2.3); dangerous-when-wet (4.3); poison-by-inhalation (6.1 in some categories); and certain radioactive materials. Table 2 hazards (most of the common ones — flammable liquids, oxidizers, corrosives, non-toxic flammable gases) require placards only when the load exceeds 1,001 pounds aggregate. The distinction matters because Table 1 materials can be lethal in tiny quantities and need maximum visibility. Cargo placarded with a Table 1 hazard must also use the corresponding identification number on or near the placard.