Dunnage, blocking and bracing are the materials and methods used to stop cargo from moving inside a container, truck or wagon. Dunnage fills voids and cushions the load, blocking prevents movement by sitting against the cargo, and bracing resists tipping and sliding forces. Wooden dunnage used in international shipments is wood packaging material and must comply with ISPM 15.
Why cargo must be secured
Cargo is not static while it travels. Trucks brake and corner, trains shunt, and ships roll and pitch, so loads are exposed to forces in several directions. A shipment that was stable when loaded can shift, tip or collapse if gaps are left or if the load is held only by friction. Shifting cargo damages goods and equipment, can injure workers who open the doors, and in extreme cases endangers vehicles and ships.
The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (the CTU Code), issued in 2014 as an update of the 1997 guidelines, is the main international reference. It is a voluntary code but is widely used as a basis for national rules and contracts. For road transport in Europe, the standard EN 12195-1 gives calculation methods for securing forces; see load securing standards.
The vocabulary
| Term | Meaning | Typical examples |
|---|---|---|
| Dunnage | Material used to fill voids, support or protect cargo | Wood beams and boards, paper or cardboard pads, inflatable bags |
| Blocking | Restraining cargo by placing solid material against it so it cannot move in that direction | Timber battens nailed to the floor, wooden frames, wedges |
| Bracing | Supporting cargo against tipping or racking, often at an angle | Diagonal timber struts, cross bracing between walls and cargo |
| Lashing | Holding cargo with straps, chains or wire to securing points | Web lashings, ratchet straps |
| Friction enhancement | Increasing grip between cargo and floor | Anti-slip mats, rubber sheets |
Most real loads use a combination. For example, heavy cases may be blocked against the front wall, lashed to floor anchors and braced sideways with timber.
Main securing methods
Blocking and bracing with timber. This is the oldest method and is still very common for heavy and irregular cargo. Timber battens are fixed to the floor around the load, or beams are wedged between the cargo and the container walls. The timber must be strong enough for the expected forces, and fasteners must not damage the container floor beyond what the operator allows. Check carrier rules, because some operators limit nailing into container floors.
Filling voids. A load that does not fill the width of a container leaves gaps. Fillers such as timber, pallets, empty crates or inflatable dunnage bags keep the cargo in contact with other cargo or the walls so that it cannot gain momentum.
Airbags (inflatable dunnage bags). Bags made of paper or plastic films are placed in voids and inflated with compressed air. They are quick to use and suit uniform cargo such as palletized goods or boxes, but they must be selected for the void size and pressure rating and need to be placed so they cannot be squeezed out. They are not a replacement for lashing in cases where the load needs positive restraint.
Lashing. Straps and chains hold cargo down or back to anchor points. The strength of lashings, their angle and the strength of the anchors determine the restraining force. See pallets in shipping containers and pallets in trucks.
Friction. Placing anti-slip material between cargo and floor increases friction, which reduces the force other methods must handle. Friction alone is generally not accepted as sufficient for heavy loads at sea.
Wood dunnage and ISPM 15
Wood used to support or protect cargo, whether or not it forms part of the packaging, is called dunnage in ISPM 15. It is within the scope of the standard when it is made of raw (unprocessed) wood. Under the standard, dunnage in international trade must be treated, normally by heat treatment, and marked with the IPPC stamp, just like pallets and crates. Wood that is thin (6 mm or less) or processed, such as plywood, particleboard or OSB, is exempt; see ISPM 15 exemptions.
Practical consequences:
- Do not use untreated or unmarked timber as dunnage in international shipments, because it can cause the shipment to be refused, treated or destroyed at the border.
- Dunnage supplied by a freight forwarder or packer should be checked for the mark, not assumed to be compliant.
- Dunnage made from plywood or paper avoids the issue; see paper and corrugated pallets for similar alternatives.
- The rules for dunnage are covered in more detail in dunnage and ISPM 15 and ISPM 15 non-compliance.
Practical planning steps
A safe load plan follows this order:
- Know the cargo. Weight, dimensions, center of gravity, stackability and surface type.
- Know the route. Road, rail, sea, or a combination, because the forces differ and the CTU Code and national rules apply different assumptions.
- Position the load. Spread weight evenly along the floor and keep the center of gravity low and central. Place the heaviest items at the bottom and near the middle.
- Eliminate gaps. Fill voids so cargo cannot build up momentum.
- Secure. Combine blocking, bracing and lashing as needed, calculating the required strength where the standard demands it.
- Check anchors. Make sure container floors and lashing points are rated for the loads.
- Document. Keep records of how the load was secured; photographs help in disputes and claims.
Palletized goods add their own steps: stretch wrap and straps hold the unit load together, and pallet stacking rules limit height; see stretch wrapping pallets and pallet stacking rules.
Common mistakes
- Relying on friction alone for heavy or smooth-surfaced cargo.
- Leaving large voids at the container doors, so cargo falls out when the doors are opened.
- Using untreated timber in international shipments.
- Using lashings that are damaged, undersized or attached to unrated anchor points.
- Placing airbags between cargo that can slip around the bag, or overinflating them.
- Ignoring the vertical gap when loads are stacked.
Frequently asked questions
What is dunnage?
Material used to fill gaps, support or protect cargo in a container or vehicle. It may be wood, paper, plastic or inflatable bags.
Does wooden dunnage need an ISPM 15 stamp?
Yes, when it is raw solid wood and travels in international trade. Plywood and similar processed panels, and very thin wood, are exempt.
Are airbags enough to secure a load?
Not always. They fill voids well for uniform cargo, but heavy or unstable loads typically also need blocking, bracing or lashing, and carriers may specify requirements.
What is the CTU Code?
A voluntary code of practice from IMO, ILO and UNECE, adopted in 2014, that gives guidance for packing and securing cargo in containers and other transport units.
Sources
- IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code) — International Maritime Organization
- CTU Code: a quick guide — International Plant Protection Convention
- ISPM 15 (2018): Regulation of wood packaging material in international trade — International Plant Protection Convention
- GDV packaging handbook — German Insurance Association (GDV)