Four Placard Holders and a One-Pound Bottle
You are dispatched from a chemical distributor in St. Louis with a mixed load for three Missouri customers. The trailer holds 12 drums of UN1263, Paint, Class 3, PG III (640 lb gross); 8 drums of UN1760, Corrosive liquid, n.o.s., Class 8, PG III (520 lb gross); one 1-lb bottle of UN2811, Toxic solid, organic, n.o.s., Class 6.1, PG I; and 300 lb gross of UN3082, Environmentally hazardous substance, liquid, Class 9, PG III. The shipper's clerk says no placards are needed because no single class is over 1,000 pounds and one of the items weighs only a pound. Your tractor has exactly four placard holders on each side and none on the front or rear. You are asked to sign the shipping paper and pull out for the first stop, 60 miles west.
1. Does this load require placards? Name every class that must be placarded and show the arithmetic you used.
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Two separate rules apply, and the clerk has blended them into one wrong one.
Rule 1, Table 1 materials: placards are required in any quantity. Class 6.1 PG I is a Table 1 entry, so the single 1-lb bottle by itself forces a 6.1 (POISON) placard. Weight is irrelevant.
Rule 2, Table 2 materials: placards are required only when the aggregate gross weight of all Table 2 hazardous material on the vehicle is 1,001 lb or more, and then you placard each class present. Add it up: 640 + 520 + 300 = 1,460 lb, which is over the threshold. That triggers placards for Class 3, Class 8, and Class 9.
Result: 6.1, 3, 8, 9. Four placards, which exactly fills your holders.
The clerk's error is treating 1,001 lb as a per-class limit. It is an aggregate across all Table 2 classes on the vehicle. Also confirm placement: both sides and both ends of the vehicle.
2. The clerk offers to put up one DANGEROUS placard to cover the whole load. Evaluate that.
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That is not what the DANGEROUS placard is for. Under 49 CFR 172.504(b), DANGEROUS may be displayed in place of the specific placards only when two or more Table 1 materials are loaded. Here you have exactly one Table 1 material (the 6.1 PG I pesticide) and three Table 2 materials, so DANGEROUS cannot substitute for the 3, 8, or 9 placards, and it is not needed for the single Table 1 entry.
Even where DANGEROUS is permitted, treat it as a convenience, not a shortcut. It deliberately withholds the specific hazard from responders approaching the vehicle; they have to open the shipping paper before they know what they are dealing with. If your holder count is the real problem, the answer is more holders or a smaller load, not a generic placard.
3. At the second stop a 25-lb carton of UN1950, Aerosols, Class 2.1, is added. You still have only four holders per side. What must be displayed, and what option does the regulation give you?
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Class 2.1 is a Table 1 entry, so the 25-lb carton requires a FLAMMABLE placard in any quantity. You now have five classes aboard: 2.1, 6.1, 3, 8, and 9.
Because you now have two Table 1 materials (2.1 and 6.1 PG I), 172.504(b) permits you to display DANGEROUS in place of both of those specific placards. That gives you DANGEROUS, 3, 8, 9, which fits in four holders.
Weigh the trade-off before you do it. The placard is what a firefighter reads first to choose an ERG guide and set an initial isolation distance; collapsing two hazards into DANGEROUS costs them that first cue. Most carriers carry spare holders and show all five. Whichever you choose, verify the aerosols really are Class 2.1, confirm the new line was added to the shipping paper, and check that your total Table 2 weight still supports the 3, 8, and 9 placards.