What is a Q-value? For dangerous goods air transport?

Introduction and Background
When a shipper packs two or more dangerous goods (or hazardous materials, hazmat) into one combination package for air transport, there are additional requirements over and above the general packing requirements and compatibility compliance within the ICAO/IATA regulations.

Shippers must also be aware of possible:

• Combustion and/or evolution of considerable heat,
• Evolution of flammable gases that asphyxiate or are toxic,
• Formation of corrosive substances, or
• Formation of unstable substances if the materials mix.

When a package contains dangerous goods of the same physical state (e.g. liquids, solids or gases), it is easy to calculate the maximum net quantity allowed in the package based on the regulations. You simply add the allowable quantity (based on their respective packing instructions) for each dangerous goods together.

This becomes difficult when your package contains dangerous goods of different physical states.

To address this issue, the ICAO Technical Instructions (TI) published a new requirement in 1985 for calculating the maximum quantity allowed for multiple dangerous goods contained in one outer packaging, regardless of the physical state. The IATA Dangerous Goods Regulations (DGR) quickly followed suit.

This new requirement was called the "Q-value". As outlined in IATA DGR 5.0.2.11(g), the Q-value is applied to packing such that, "the quantities of different dangerous goods contained in one outer packaging must be such that "Q" does not exceed the value of 1.0."

Applicability
The Q-value is calculated by using the formula of:

Where n₁, n₂, etc. are the net quantities per package of the different dangerous goods, and M₁, M₂, etc. are the maximum net quantities allowed per package for these different dangerous goods according to the List of Dangerous Goods in Section 4 of the IATA DGR.

The sum, Q, must be equal to or less than 1. The sum must be rounded up to the nearest tenth (or first decimal place). This formula is applicable whenever more than one dangerous goods is packed or contained within a combination package intended for air transport.

Example
A shipper is shipping the following dangerous goods contained in the same outer fiberboard box:

• 1.0 Liter of UN1114, Benzene, Class 3, PG II, using packing instruction 353
  (max. net quantity per package for 353 is 5 Liters)
• 2.0 kilograms of UN2803, Gallium, Class 8, PG III, using packing instruction 867
  (max. net quantity per package for 867 is 20 kilograms)

The Q-value for this package is calculated with the following equation:

This gives a Q-value of 0.3. Since the Q-value is equal to or less than 1, these dangerous goods quantities may be all packed into one 4G fiberboard box. If the Q-value exceeded 1, the quantities of dangerous goods would have to be reduced until the Q-value of 1 or lower is achieved.

Exclusions
The following dangerous goods are not considered in the calculation of the Q-value:

• UN1845, Dry ice,
• Those where Columns J or L in the IATA List of Dangerous Goods indicate "No Limit",
• Those with the same UN number, packing group and physical state (e.g. solid or liquid), provided they are the only dangerous goods in the package and the total net quantity does not exceed the maximum  net quantity shown in the List of Dangerous Goods, or
• Those where Columns J or L in the IATA List of Dangerous Goods indicate a gross weight per package.

Considerations
There are additional considerations to take into account when dealing with multiple dangerous goods being packed into one outer package.

These can include (but are not limited to):

• IATA DGR 8.1.6.9.2(f) for describing how these packages are declared on the shipper's declaration for dangerous goods:
• For one package, the phrase "All Packed in One (description of package type)" must immediately follow the relevent entries (e.g. "All Packed in One Fiberboard Box"), and
• For multiple packages, the phrase "All Packed in One (description of package type) x (number of packages)" must immediately follow the relevant entries (e.g. "All Packed in One Fiberboard Box x 3").
• The outer package must be allowed for all dangerous goods contained within it,
• The outer package must meet the specification performance tests for the most restrictive packing group of the a substance or article within the package,
• Must comply with inner packaging requirements, and
• When a package contains a dangerous goods with the letter "G" following the quantity shown in Columns J or L in the IATA List of Dangerous Goods, the gross weight of the completed package does not exceed the lowest applicable gross weight.

Other considerations (including Limited Quantities, special provisions, etc.) will be saved for a future discussion.

Regulatory Staff
Bureau of Dangerous Goods, Ltd.