Container Dunnage: Airbags, Blocking, Bracing and Void Fill

Dunnage is any material used to fill gaps and hold cargo in place inside a container: inflatable airbags, timber blocking and bracing, cardboard or foam void fill, and the lashings that tie cargo to the container's lashing points. The aim is simple: the cargo must not be able to move forwards, backwards, sideways or upwards. The best way to need less dunnage is to plan the load so the gaps are few, small and in places you can fill.

The reference for good practice is the CTU Code (the IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units). This article is general guidance, not a securing calculation; for heavy or unusual cargo, use a securing specialist.

Why containers need securing

At sea a container rolls, pitches and heaves; on the road it brakes and corners; at the terminal it is lifted and set down. Cargo with room to move builds up speed over even a few centimetres and hits the walls or the doors. Typical consequences are crushed cartons, broken pallets, punctured drums and, worst, cargo falling when the doors are opened.

The main securing methods

Using airbags correctly

• Size the bag to the void. Each airbag size is rated for a maximum gap width, set by the manufacturer. Wider voids should be reduced first with timber or a different layout.
• Never against the doors. An airbag must sit between cargo units, not between cargo and the doors, which are not a restraint.
• Smooth, flat faces. Bags placed against sharp edges, pallet corners or uneven surfaces can burst; protect them with cardboard or boards.
• Inflate to the specified pressure. Over-inflation can damage cartons; under-inflation lets the cargo move.
• Cover the load face. The bag should bear on the strong part of the cargo, usually low on pallets, not on a single fragile carton.

Blocking, bracing and lashing points

Blocking timber should bear on the cargo over a wide area and be fixed so it cannot fall out of place. At the door end, a timber gate or bulkhead across the width, held against the corner posts or by braces to the floor, keeps the last row off the doors.

Lashing points in the floor rails and on the corner posts have a rated capacity that is lower than many people expect, and it varies by container. Check the markings or the operator's data before relying on them, use several points rather than one, and don't lash to the side wall panels, which are not designed for it.

Planning to minimise voids

Dunnage costs money and loading time, and every void is a place where something can go wrong. The plan decides how many voids there are and where they end up.

1. 1Choose a layout that leaves one predictable gap. In a container about 2.35 m wide, two lanes of different pallet orientation (1,200 + 800 mm) leave about 350 mm; two lanes of Euro pallets on their narrow side leave about 750 mm. The first is far easier to secure. See how many pallets fit in a container.
2. 2Put the gap where you can fill it. A single gap down the middle can take one line of airbags; two small gaps at the walls are harder to fill evenly.
3. 3Keep rows square. Ragged rows create many small voids instead of one manageable one.
4. 4Fill gaps with cargo first. Small cartons from the same shipment are better void fill than airbags.
5. 5Plan the door end. Know in advance whether the last row ends flush across the width, and what blocks it.
6. 6Keep heavy items blocked to the floor. Heavy items standing alone need blocking on all sides or lashing; place them against other cargo where possible.

Worked example: securing pallets in a 40'

Say you are loading 22 Euro pallets, 1.4 m high, into a 40' container with typical inside dimensions of 12.03 × 2.35 m.

1. 1Layout: lane A with pallets crosswise (800 mm along the length) and lane B lengthwise (1,200 mm along). 13 pallets in lane A use 10.4 m; 9 in lane B use 10.8 m. Both lanes stop more than a metre short of the doors.
2. 2Side gap: 2,350 − (1,200 + 800) = about 350 mm. Push lane A against one wall and lane B against the other, leaving the gap in the centre. One line of airbags sized for a 350 mm void, placed so every pallet bears on a bag, stops sideways movement.
3. 3Door-end gap: 12.03 − 10.8 = about 1.2 m behind lane B and 1.6 m behind lane A. That is too large for airbags. Build a timber bulkhead across the width against the last pallets and brace it to the floor or corner posts, with a step or separate blocking for each lane so both rows are held.
4. 4Front wall: both lanes start tight against the front wall, so no blocking is needed there.

The same 22 pallets in two straight lanes of Euro pallets on their narrow side would leave a 750 mm centre gap, needing much more dunnage. Planning the layout first is what keeps securing simple.

A 3D plan makes the gaps visible before loading. In EveryLoading, the top and rear views of a container plan show where the empty space is, and you can drag items to move gaps to where they can be filled. The PDF plan gives the loading crew the layout, so the dunnage can be prepared in advance. For weight distribution and the overall stuffing method, see container stuffing plan; for the road-side principles behind restraint, see load securing basics.