Placards, Acid on Top, and a Heavy Supersack Load
A highway carrier builds a load at a distribution centre. The trailer is to contain 80 drums of UN1263 PAINT, Class 3, PG II, each 25 kg gross (2,000 kg); 20 drums of UN1789 HYDROCHLORIC ACID, Class 8, PG II, each 30 kg gross (600 kg); and 15 supersacks of UN3077 ENVIRONMENTALLY HAZARDOUS SUBSTANCE, SOLID, N.O.S., Class 9, PG III, each 1,000 kg gross (15,000 kg). The dock supervisor plans to place the acid drums on top of the paint drums to save floor space, then the supersacks on top. The trailer has placards for Class 3 and Class 9 on both sides and the rear, but none for Class 8. The driver's shipping document lists all three entries and a 24-hour emergency number. The supersacks are not palletized and have no tie-down points. The acid drums are plastic with screw caps. The dispatcher asks whether the Class 8 placards are missing and whether the loading pattern is acceptable.
1. Determine which placards the trailer requires, showing your calculation.
Read the worked answer
Placarding is assessed by class, not by adding all dangerous goods together. Class 3 is 80 x 25 kg = 2,000 kg gross, which exceeds 1,000 kg, so Class 3 placards are required. Class 9 is 15 x 1,000 kg = 15,000 kg gross, which exceeds 1,000 kg, so Class 9 placards are required. Class 8 is 20 x 30 kg = 600 kg gross, which does not exceed 1,000 kg, so Class 8 placards are not required for this load.
The trailer's current placards are therefore correct for placarding, assuming no other Class 8 goods are added. The dispatcher's concern about missing Class 8 placards is misplaced for this quantity. The Class 8 packages must still bear Class 8 labels, and the shipping document must still describe the acid accurately. Placarding is not a substitute for package labels.
2. Evaluate the proposed loading pattern and identify the hazards and required controls.
Read the worked answer
Putting acid drums on top of paint is poor practice. The acid is a Class 8 corrosive in plastic drums with screw caps; a cap leak or a cracked drum can drip onto the paint drums below, damage labels and closures, and create a mixed corrosive/flammable spill. Acid should go on the floor or in a containment tray, not above other goods. The 1,000 kg supersacks should not be stacked on top of drums; they can crush or distort the drums and make unloading unsafe.
The load should be rebuilt: heavy supersacks on the floor or on a load deck, weight distributed, drums blocked and braced, and acid separated or contained. The supersacks need restraint even without tie-down points, using load bars, dunnage, or a contained bay. The spill kit should be accessible. The trailer should retain the Class 3 and Class 9 placards and the Class 8 package labels.
3. At the next stop, the carrier adds acid drums. Does the placarding change with 10 more drums (300 kg)? With 15 more drums (450 kg)?
Read the worked answer
With 10 more acid drums, Class 8 becomes 600 + 300 = 900 kg gross. That is still below 1,000 kg, so no Class 8 placard is required. With 15 more acid drums, Class 8 becomes 600 + 450 = 1,050 kg gross. That exceeds 1,000 kg, so Class 8 placards are required in addition to the existing Class 3 and Class 9 placards.
The carrier should verify actual gross mass rather than estimate from net acid weight, because the threshold is close at 1,050 kg. The shipping document must be updated for the added acid, and the load pattern must still keep acid from draining onto other goods. This is a classic judgment point: a small addition can trigger a new placard class.