General Packing Requirements, Single vs. Combination Packaging & Ullage Rules
Key Takeaways
- IATA DGR Section 5 General Packing Requirements (5.0.2.1 through 5.0.2.14) govern structural integrity, chemical compatibility, pressure resistance, and closure standards for all dangerous goods air shipments.
- Combination packaging consists of one or more inner packagings secured inside a protective outer packaging, whereas single packaging holds liquid or solid dangerous goods directly without inner receptacles.
- Liquid filling limits require a minimum ullage (outage) so that receptacles are filled to a maximum of 98% capacity at 55°C (131°F) to prevent liquid-full conditions during flight.
- Packaging materials, gaskets, and closures must be chemically inert to the dangerous goods contained, preventing permeation, embrittlement, or dangerous chemical reactions.
- Inner receptacles containing liquids must utilize positive locking mechanisms or secondary closures to resist vibration-induced loosening during flight.
General Packing Requirements, Single vs. Combination Packaging & Ullage Rules
The air transport environment subjects cargo to dynamic stresses rarely encountered in surface transport. High-altitude flight involves rapid atmospheric pressure changes, continuous high-frequency vibration, extremes of ambient temperature (-40°C in unheated compartments to +55°C on tropical tarmac aprons), and multi-directional accelerations during takeoff, turbulence, and landing. To safeguard the aircraft structure, flight crew, and general public, IATA Dangerous Goods Regulations (DGR) Section 5 establishes strict statutory and operational standards for packaging dangerous goods.
1. Overview of DGR Section 5 General Packing Requirements (5.0.2.1 – 5.0.2.14)
All dangerous goods tendered for air transport must be prepared in packagings of high quality, constructed and securely closed to prevent any leakage caused by changes in temperature, humidity, pressure, or vibration under normal conditions of transport. The shipper is legally responsible for selecting and assembling compliant packaging.
Key Subsections of DGR 5.0.2
- Quality & Structural Integrity: Packagings must be manufactured and closed so that under normal transport conditions, no dangerous goods can escape. No harmful quantity of hazardous vapor can permeate the packaging.
- Responsibility of Shipper: The shipper must ensure that the packaging complies with all general requirements, specific Packing Instructions, and applicable UN specification standards.
- Chemical Compatibility: Materials of which the packaging and any closures are made must not be liable to react dangerously with the contents or be significantly weakened by them.
- DGR 5.0.2.5 (Closure Security): Screw caps, stoppers, and friction closures on inner packagings must be held securely in place by positive means (e.g., secondary locking rings, adhesive tape, or heat-shrink bands) to resist vibration and pressure shifts.
- DGR 5.0.2.8 (Ullage / Outage Requirements for Liquids): Receptacles must not be completely filled with liquid. Sufficient vacant space (ullage) must remain to accommodate liquid expansion caused by temperature increases during flight.
- Cushioning & Absorbent Materials: Inner packagings within combination packagings must be cushioned against movement. Combination packagings holding liquid dangerous goods in Packing Group I or II require absorbent material capable of absorbing the entire liquid contents of the inner packagings.
- Venting Prohibitions: Packages containing dangerous goods must not vent gas or pressure during transport unless specifically authorized by the Packing Instruction (e.g., cryogenic liquids or dry ice).
2. Single Packaging vs. Combination Packaging
Dangerous goods packagings are classified into two primary structural forms: single packagings and combination packagings.
+-------------------------------------------------------------------------+
| PACKAGING TYPES IN DGR |
+------------------------------------+------------------------------------+
| SINGLE PACKAGING | COMBINATION PACKAGING |
| +--------------------------------+ | +--------------------------------+ |
| | Outer Container Directly | | | Outer Packaging (e.g. 4G Box) | |
| | Holding Contents | | | +----------------------------+ | |
| | (e.g., Steel Drum 1A1) | | | | Inner Receptacles (Glass, | | |
| | | | | | Metal, or Plastic Bottles) | | |
| | | | | +----------------------------+ | |
| | | | | Inert Absorbent/Cushioning | |
| +--------------------------------+ | +--------------------------------+ |
+------------------------------------+------------------------------------+
Single Packaging Mechanics
A single packaging consists of a single outer container that directly retains the hazardous liquid or solid without any internal receptacles. Examples include non-removable head steel drums (1A1), plastic jerricans (3H1), or composite packagings with an internal plastic liner bonded within a steel shell (6HA1).
- Air Transport Restrictions: Single packagings are subject to strict volumetric limits and are forbidden for certain high-hazard liquids (e.g., Packing Group I corrosive or toxic liquids) on passenger aircraft. Single packagings containing liquids must pass rigorous internal hydrostatic pressure testing.
Combination Packaging Mechanics
A combination packaging consists of one or more inner packagings (receptacles made of glass, plastic, metal, or earthenware) placed inside a protective outer packaging (such as a fibreboard box 4G, wooden box 4C1, or steel drum 1A2).
- Absorbent & Cushioning System: Inner packagings must be packed with inert cushioning material (such as vermiculite, expanded polystyrene, or polypropylene pads) to prevent breakage. For liquid dangerous goods of Packing Group I or II, the cushioning must include sufficient absorbent material to absorb the entire liquid contents of all inner packagings.
Structural Comparison Matrix
| Attribute | Single Packaging | Combination Packaging |
|---|---|---|
| Primary Mechanism | Outer vessel directly contacts dangerous goods | Receptacle inside an outer box/drum |
| Inner Receptacles | None | Glass, plastic, metal, or paper inner containers |
| Absorbent Required | Not applicable | Mandatory for PG I & II liquids |
| Common Air Example | Heavy steel drum (1A1) or plastic jerrican (3H1) | Fibreboard box (4G) with glass inner bottles |
| Vibration Integrity | Relies on primary drum bung and gasket seal | Relies on inner cap secondary seal plus cushioning |
| Pax Aircraft Use | Restricted or prohibited for high-hazard liquids | Preferred method for small volume liquid/solid goods |
3. Liquid Ullage (Outage) Rules & Expansion Calculations
When an aircraft ascends to cruising altitude (30,000 to 41,000 feet), ambient cargo hold temperature and pressure fluctuate. If a container is filled to 100% capacity at ground level, thermal expansion of the liquid will create enormous hydraulic force, fracturing the vessel or forcing open closures.
The Mandatory 98% Ullage Limit at 55°C
To prevent liquid-full conditions, DGR 5.0.2.8 mandates that liquid dangerous goods must not completely fill a receptacle at 15°C. Sufficient vacant space (ullage or outage) must remain to ensure that the packaging will not become liquid-full at a temperature of 55°C (131°F).
Operational Expansion Calculation
The required expansion space depends on the liquid's cubical coefficient of thermal expansion ($\alpha$). The regulation states the outcome — the receptacle must not be liquid-full at 55°C — and leaves the arithmetic to the shipper. Working backwards from a 98% ceiling at 55°C, the maximum degree of filling at the filling temperature ($t_f$) is:
Where:
- $\alpha$ = Cubical expansion coefficient per degree Celsius between 15°C and 55°C.
- $t_f$ = Temperature of the liquid at the time of filling (°C).
Practical Example
If a flammable liquid has a high thermal expansion coefficient ($\alpha = 0.0015\text{ / }^\circ\text{C}$) and is filled at a cold warehouse temperature of $t_f = 15^\circ\text{C}$:
Thus, at $15^\circ\text{C}$, the shipper must fill the container to no more than 92.45% of total volumetric capacity, leaving a 7.55% minimum ullage space at fill time so that expansion at $55^\circ\text{C}$ remains safely within the 98% limit.
4. Chemical Compatibility, Materials & Closure Standards
Packaging materials and closures must be chemically compatible with the dangerous goods they enclose.
Chemical Compatibility Risks
- Corrosive Degradation: Strong acids (e.g., nitric acid) corrode mild steel drums; strong bases degrade aluminum.
- Solvent Permeation: Organic solvents (e.g., acetone, toluene) permeate polyethylene walls, softening plastic jerricans over time.
- Embrittlement & Stress Cracking: Halogenated hydrocarbons cause environmental stress cracking in synthetic polymers under mechanical load.
Closure Integrity Standards
Under DGR 5.0.2.5, all closures on inner liquid packagings must be secured against backing off or loosening caused by flight vibration or thermal cycling. Acceptable secondary closure methods include:
- Threaded Screw Caps: Secured with secondary friction sleeves, heat-shrink bands, or locking ratchets.
- Stoppers & Bungs: Retained by wire ties, metal crimp seals, or positive mechanical locking rings.
- Heat-Sealed Foil / Poly-Liners: Primary liquid seal beneath a secondary threaded cap.
In addition, friction stoppers (such as glass stoppers in laboratory bottles) must be held tightly in place by wire ties, tape, or positive mechanical clamps; friction closures alone are strictly prohibited for liquid dangerous goods in air transport.
Under IATA DGR Section 5 (5.0.2.8), what is the maximum allowable liquid filling limit for a dangerous goods receptacle at 55°C (131°F)?
Which of the following correctly describes the key distinction between single packaging and combination packaging?
Why are friction stoppers without secondary locking mechanisms forbidden on inner liquid packagings in air transport?