Dunnage

Dunnage is the material packed around and under cargo in a container, truck or ship's hold to support it, keep it off the floor, fill the gaps and stop it moving. The usual kinds are timber battens, blocks and beams, empty pallets, boards, inflatable dunnage bags (air bags) and rubber or other friction-increasing mats. International guidance on using it is in the CTU Code, the IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units, endorsed in 2014 and published by the IMO as MSC.1/Circ.1497. The code is non-mandatory guidance.

What dunnage does

• Blocking and bracing: timber beams and frames, empty pallets or dunnage bags are fitted into the gaps between the cargo and the walls of the container, or between packages, so the forces are carried in compression (CTU Code annex 7, 2.3.1)
• Filling voids: the code says the total of the void spaces in any horizontal direction should not exceed 15 cm, and should be smaller still between dense, rigid items such as steel, concrete or stone. Material that can deform or shrink, such as gunny cloth or weak foam, should not be used to fill them (annex 7, 2.3.6)
• Spreading the load: a heavy piece with a small footprint should have its weight transferred to the container's bottom girders, for example by bedding it on timber or steel beams designed in consultation with the container operator (annex 7, 1.10 and 3.1)
• Keeping cargo dry: timber and pallets bring moisture into a closed box. The code estimates the moisture content of dry dunnage, pallets and packing at 12% to 15%, enough to hold the air in a closed box at about 60% to 75% relative humidity, and recommends actively drying the dunnage and packing or using desiccants (annex 3, 4.2)

Dunnage bags

Air bags fill gaps between loads. The CTU Code says to follow the maker's instructions on inflation pressure and the maximum gap, to protect the bags from rough surfaces that can chafe or pierce them, and not to use them to fill the space at the doorway unless precautions ensure they cannot force the doors open violently when the doors are opened (annex 7, 2.3.8).

Wood dunnage and ISPM 15

• In scope: ISPM 15, the IPPC standard on wood packaging material, expressly covers dunnage and notes that dunnage in particular has been shown to carry a high risk of spreading quarantine pests
• US rule: the US definition of regulated wood packaging material names dunnage alongside crating, pallets, packing blocks, drums, cases and skids (7 CFR 319.40-1). It must be treated and carry the IPPC mark (7 CFR 319.40-3(b)), and an inspector at the port of first arrival may order unmarked wood packaging re-exported (319.40-3(b)(3)). Manufactured wood such as plywood, and wood pieces under 6 mm thick, fall outside the definition
• Marking offcuts: dunnage is often cut to length at loading, so ISPM 15 asks that the mark be applied along the whole length at short intervals, and says small pieces that do not carry the complete mark should not be used

Heavy cargo: stone, granite and machinery

The CTU Code says granite and marble blocks can go in closed containers but cannot simply be stowed from wall to wall: they need bracing and blocking against the container frame, lashing to the securing points, or both. Because the securing points in a general-purpose container have limited capacity, it notes that a standard box may not suit some large, heavy pieces, and a platform or flat rack can be used instead (CTU Code 7.2.5). Stone slabs and granite are regular cargo on the India to USA lane. Remember that all dunnage and securing material inside the box counts toward its verified gross mass.

Common mistakes

• Unmarked or partly marked timber, which an inspector at the US port can order re-exported, with the load it braces at stake
• Wet timber, which adds moisture that condenses on the cargo during the voyage
• Nailing blocks into the floor of a closed container: the code says wooden floors of closed containers are generally not suitable for nailing, and battens should be nailed only to dunnage or timbers under the cargo (annex 7, 2.3.5)

At destination the consignee removes the dunnage, bags and bracing, and the code asks that timber without the IPPC mark be disposed of under the local plant protection rules. For heavy or awkward cargo, see FCL ocean freight and the lashing entry.