The general rule is going to be: If in bulk, you always need a placard. If non-bulk, then it depends on if the hazard class is in Table 1 or 2, and the amount that is being shipped. Also, in most cases, 4 placards are required, one on each side and one on each end.

Where do placards have to be placed?

Location of placards

An outer warning placard must be displayed on every entrance to a workplace so that it is clearly visible from normal approaches. Information placards must be located within the workplace at the relevant storage location so that they are clearly visible from normal approaches.

When should a dangerous placard be used?

The use of the DANGEROUS placard is to be used for shipments of two or more hazardous materials found in Table 2 only. Finally, when 1,000 kg (2,205 lbs) or more of one category of material is loaded at one loading facility.