Labeling: Hazard Labels, Subsidiary Labels, and Placement
Labeling is the package hazard-diamond domain. The exam tests whether you can match a package's hazard class to the correct label, add subsidiary labels, place labels correctly, and remove labels when they no longer apply.
Label basics
A label is a square-on-point hazard warning at least 100 mm (3.9 in) on each side. The primary label matches the material's hazard class or division; subsidiary labels show additional hazards. For example, a Class 3 flammable liquid gets a red FLAMMABLE LIQUID label, while an oxidizer gets a yellow OXIDIZER label. Labels must be printed on or affixed to the outside of the package, on a contrasting background, and must not be obscured by tape, straps, or markings. At least one label must be visible; for many packages the label is placed near the closure or on the side, not the bottom.
Subsidiary labels
When the Hazardous Materials Table lists a subsidiary hazard, the package needs the corresponding subsidiary label in addition to the primary label. A package of nitric acid, for example, carries the Class 8 corrosive label and a subsidiary Class 5.1 oxidizer label. The shipping paper's parentheses are your clue: "UN2031, Nitric acid, 8, (5.1), PG II" tells you that two labels are required.
Changing and removing labels
A label may be applied only to a package that actually contains the material indicated by that label. When a package is emptied or its contents are changed, old labels must be removed or obscured so the package does not display a false hazard. Do not put a placard on a package in place of a label; placards are for vehicles and bulk packages.
Worked example
A driver is loading a drum described as "UN1789, Hydrochloric acid, 8, PG II." The drum has a red FLAMMABLE LIQUID label. That is wrong: hydrochloric acid is a Class 8 corrosive, so the package needs a CORROSIVE label, not a flammable liquid label. The driver should refuse the package until the label is corrected, because the label must match the shipping paper and the hazard class. If the paper had shown a subsidiary hazard, the matching subsidiary label would also be required.
Traps
The most common mistakes are using the label for the wrong class, omitting a subsidiary label, covering a label with tape or a shipping label, leaving an old label on a reused package, and thinking a label is optional because the package is small. Labels are not interchangeable with markings or placards: each has a different job.