Can a Y case carry group I cargo?

A: No. Y covers PG II and PG III only. Group I needs X, which lifts the drop from 1.2 m to 1.8 m and the latches from 2 to 4.

Is the 24 h seawater immersion mandatory?

A: A sea-freight addition. Where the contract names it, run 24 h and stack within 2 h, deflection under 0.5 mm.

Where does the marine pollutant mark go?

A: Right of the UN mark, 50 mm away, both on a flat panel. Across a rib, a scan rejects it.

Is the 6 m separation measured from the wall or the pallet?

A: From the outermost point. A pallet overhanging 100 mm moves the reference, and 0.3 m decides the case.

How does a 1200 kg item ship?

A: Above 1000 kg it goes on a flat rack with its own plan; four-point lashing covers 1000 kg or less.

IMDG Packing Groups

Quick answer: Imdg packing assigns X, Y or Z from the packing group, and the case only has to prove it meets the drop the cargo already set.

Packing groups X, Y and Z
Turning the three thresholds into a drawing
Marking at 12 mm, plus one marine pollutant P
Three segregation relations on deck
Lashing: four points and a 1000 kg ceiling
FAQ

1. Packing groups X, Y and Z

The hazard of the cargo sets the packing group; the group sets the letter on the case. PG I takes X, PG II takes Y, PG III takes Z. Those letters are not grades of quality, they record which performance test the shell has passed.

Compatibility runs downhill only: X carries I, II and III, Y carries II and III, Z carries III alone. A Z case loaded with group II cargo is intact but its report no longer matches, so an inspector treats it as unmarked.

Group	May carry	Drop height	Stack condition	Typical gross
X	I, II, III	1.8 m	3 m for 24 h	800 kg to 1000 kg
Y	II, III	1.2 m	3 m for 24 h	500 kg to 800 kg
Z	III	0.8 m	3 m for 24 h	300 kg to 500 kg

The drop heights differ by more than a factor of two, and foam cannot close that gap. On the same 600 × 400 × 300 mm envelope, an X shell runs 5 mm wall and 4 latches, a Z shell 3.5 mm and 2, 1.8 kg apart.

2. Turning the three thresholds into a drawing

Fix the attitude before the height reaches a drawing. Sea freight drops on the worst corner: a 28 kg X case falling 1.8 m onto steel has to absorb about 494 J there, which sets corner block thickness and radius together.

Imdg packing line under galvanised spiral duct and insulated pipes on yellow steelwork, a white distribution board with a red sign

Corners form at R8, ribs sit 120 mm apart and stand 4 mm high, and lid clearance stays inside 1.5 mm. Latches follow the grade: 4 on an X case, two carrying load, two stopping lift.

Stacking runs to 3 m for 24 h on the bottom case. Three 700 kg X cases put 1400 kg on the lowest, near 0.9 MPa in the wall; a 5 mm PP shell may deflect 1.2 mm there, and past 3 mm it needs internal ribs.

Seawater is the condition only sea freight adds. Immerse the case for 24 h, dry it, stack within 2 h, and keep added deflection under 0.5 mm. Salt creeps into regrind pores, and shells above 30% regrind fail here.

All three grades end on one drawing, separated by three numbers: wall, latch count, corner blocks. One set per grade beats redesigning each order.

3. Marking at 12 mm, plus one marine pollutant P

The UN mark carries four parts: packaging symbol, group letter, material code, manufacturing line. Letters stand at 12 mm or more, every package is marked, and the mark sits on a flat panel rather than across a rib.

Marks must match the report item by item. An X case stamped Y, or a year off by one, is a mismatch: fixable before packing, fatal at the quay.

Marine pollutant cargo adds a second mark, to the right of the UN mark with 50 mm between them so neither is hidden in a scan.

Weather resistance follows the route: ink holds grade 3 through 96 h of salt spray, and equatorial voyages add 200 h of UV with under one colour step of fade. Wipe the panel with ethanol first, since release agent kills the adhesive at 40 °C.

4. Three segregation relations on deck

Loaded cases still keep their distance. The table reduces to three relations: away from, separated from, and separated by a bulkhead or a complete compartment. Each has a physical meaning, and mixed loads follow the strictest one.

Imdg packing mould workshop with a yellow hoist hook above blue racking, rows of steel moulds, a worker in a red helmet at the machine

Away from is 3 m horizontally, side by side in one hold with an access lane. Separated from is 6 m, or a steel bulkhead between. By a bulkhead means different compartments with one tier of vertical offset. Size plays no part; only the pair of hazard classes decides.

Measure wall to wall. When a pallet overhangs by 100 mm the pallet edge is the reference, which costs 0.3 m in practice.

Relation	Horizontal gap	Physical measure	Typical pair
Away from	3 m	Same hold, access lane	Acid and alkali
Separated from	6 m	Steel bulkhead or hold section	Oxidiser and flammable
By a bulkhead	Different holds	One tier offset	Toxic and foodstuffs

Loading order follows: of two cargoes that must be separated, the first sits near the door and the second at the far end, so a mid-voyage check need not empty the box. Reverse it and one inspection costs 40 min.

5. Lashing: four points and a 1000 kg ceiling

Above 1000 kg the item leaves the standard container for a flat rack or breakbulk, and the plan is recalculated. Under 1000 kg, four points are used: one per bottom corner, straps at 30° to 60°, pretensioned to 1.5 kN.

Those points sit on the pallet and the floor rails, not on the case. What the case offers is a corner that takes tension: 6 mm fittings, 20 mm lashing holes, 25 mm from hole edge to wall.

Lashing point	Count	Load per point	Method
Bottom corners	4	3 kN	Crossed straps
Pallet bearers	2	2 kN	Wedge and nail
Floor rails	2 sides	4 kN	Adjustable prop
Top batten	1	1 kN	Anti-lift

Leave inspection clearance: 50 mm to the side wall, 100 mm at the top, so a check can reach the cargo. Pack it solid and the whole box returns to port.

One declaration covers each shipment, and its group letter, piece count and gross weight must match the marks. Classification and declaration are issued by an accredited body; the case is outer packaging and fixing.

Conclusion

Imdg packing runs in four steps: group, mark, segregation, lashing. The first two decide whether the case boards at all. Match X, Y and Z to PG I, II and III and the 1.8 m, 1.2 m and 0.8 m drops carry meaning; set 12 mm lettering on flat panels and the quay check passes; apply the 3 m, 6 m and bulkhead rules at their strictest. Beyond that sit four lashing points and a 1000 kg ceiling.

This article covers case-side specifications only and does not address any handling, loading or use of the contents.