4. CTU Code: What It Says About Dunnage Bags (Cargo Securing Cushions)

Its main purpose is to provide guidelines for the safe packing, securing, and handling of cargo transport units (CTUs), including containers, swap bodies, semi-trailers, and other freight units used in intermodal transport (sea, road, and rail).

The CTU Code aims to:

• Ensure safety for people, property, and the environment.

• Prevent cargo damage during handling and transport.

• Harmonize good practices worldwide across the logistics and shipping industries.

Although not legally binding in every country, the CTU Code serves as a global reference standard used by shippers, carriers, freight forwarders, and insurers.

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Why Dunnage Bags Matter in Cargo Transport

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During transportation, cargo is subjected to accelerations, vibrations, and shifting forces. If cargo inside a container or trailer is not properly secured, it can move, slide, or topple — causing severe damage or even accidents.

Dunnage bags (also known as inflatable airbags or cargo securing cushions) are widely used to fill empty spaces between cargo items and prevent movement. However, their safe and effective use requires following specific rules — and that’s where the CTU Code provides detailed guidance.

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What the CTU Code Says About Dunnage Bags

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The CTU Code discusses the use of dunnage bags in Annex 7, Appendix 4, under the section “Cargo securing with dunnage bags.”

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📜 Official Excerpt from the CTU Code (UNECE, 2022)

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4 Cargo securing with dunnage bags
4.1 Introduction
4.1.1 Accelerations in different directions during transport may cause movements of cargo, either sliding or tipping. Dunnage bags, or air bags, used as blocking devices may be able to prevent these movements.

4.1.2 The size and strength of the dunnage bag are to be adjusted to the cargo weight so that the permissible blocking capacity of the dunnage bag, without risk of breaking it, is larger than the force the cargo needs to be supported with:
BC_dunnage-bag ≥ F_cargo

4.2 Force on dunnage bag from cargo (F_cargo)
4.2.1 The maximum force, with which rigid cargo may impact a dunnage bag, depends on the cargo’s mass, size and friction against the surface and the dimensioning accelerations according to the formulas below.
(Source: UNECE – CTU Code, 2022)

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You can read the official PDF on the UNECE website:
https://unece.org/sites/default/files/2022-06/Dunnage-Bags_CTU-Code_2022_12_SSP_ETS_12_final.pdf

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Understanding the CTU Code Requirements

The CTU Code highlights several key principles:

1. Function
   Dunnage bags are used to fill voids and prevent cargo movement during transport.

2. Sizing and Strength
   The blocking capacity (BC) of a dunnage bag must be equal to or greater than the force exerted by the cargo (F_cargo).
   This ensures the bag won’t burst under load.

3. Force Calculation
   The CTU Code provides formulas to estimate the forces acting on the bag based on:

   • Cargo mass (m)

   • Acceleration during transport (c)

   • Friction coefficient (µ)

   • Geometry of the load (width/height ratio b/h)

   Example formulas:

   • Sliding: F = m × g × (c − µ × 0.75 × c)

   • Tipping: F = m × g × (c − (b/h) × c)

4. Proper Installation
   Dunnage bags should be installed in stable voids, inflated with controlled pressure, and not over-inflated, as this may damage cargo or rupture the bag.

5. Complementary Use
   Dunnage bags are not a substitute for proper lashing or blocking (belts, bars, chains, or bracing). They should be part of a combined securing system.

6. Environmental and Pressure Considerations
   Temperature and air-pressure changes (e.g., during sea or air transport) can affect bag pressure. Always consider these when inflating.

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Best Practices for Using Dunnage Bags (CTU Code-Compliant)

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To ensure your cargo meets CTU Code safety standards:

✅ Select the right bag type
Choose bags that match the cargo’s weight, size, and transport mode. Materials include kraft paper, woven polypropylene, or composite laminates.

✅ Inspect before use
Check for damage, leaks, or wear. Do not reuse damaged bags.

✅ Inflate correctly
Use regulated air systems with gauges. Never exceed the manufacturer’s recommended pressure.

✅ Fill voids properly
Bags are effective for voids up to 15 cm (6 inches) or more when combined with solid blocking, depending on the container’s structure.

✅ Combine with other securing methods
Use dunnage bags together with lashing, friction mats, blocking or bracing, especially for heavy or irregular cargo.

✅ Train your staff
Operators should be familiar with the CTU Code’s cargo securing principles to minimize risk.

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Why Compliance Matters

According to UNECE and IMO, a significant portion of cargo incidents stem from improper packing and securing. Following the CTU Code helps you:

• Reduce cargo damage and insurance claims.

• Prevent workplace injuries and environmental harm.

• Ensure compliance with international standards.

• Build a reputation for professionalism and safety.

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Conclusion

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The CTU Code is the international benchmark for safe cargo packing and securing. When it comes to dunnage bags, the code clearly outlines their correct sizing, use, and limitations.

By applying these principles — proper force calculation, controlled inflation, and integration with lashing and blocking — you not only comply with global safety standards but also protect your cargo, your equipment, and your reputation.

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References:

• UNECE. CTU Code: Code of Practice for Packing of Cargo Transport Units (2022).

• IMO / ILO / UNECE Joint Publication.

• https://unece.org/transport/intermodal-transport/imoilounece-code-practice-packing-cargo-transport-units-ctu-code

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