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UN Specification Marking: “S” vs “S”

If you use UN packaging, I’m sure you are aware of the UN Specification marking that is printed on it. The UN specification marking is comprised of a series of codes separated by slashes that provide relevant information about the package being shipped. Learn more about UN markings in our article titled “What Do UN Markings on Packages Mean?”.

If your packaging has an “S” printed on it, it may not be as straight forward as you would think. The “S” can actually have two different meanings depending on how the packaging was tested and what the packaging was tested with.

“S” vs. “S”

In both the 49CFR and the TP14850, there are very clear instructions on how to properly mark a UN rated packaging. For example, in the 49CFR 178.503 (a)(5)(ii), it says for packagings intended to contain solids or inner packagings, the letter “S” must appear in the UN specification marking. Similarly, the TP14850 at says that the letter “S” must not be marked on a container unless a representative prototype of the container was successfully tested in accordance with chapter 7 with solids, viscous liquids or inner packagings.  This means that if a combination UN packaging is tested, with inner packagings (such as bottles) and an outer packaging (such as a 4G box), that the UN specification code must include the letter “S” because the combination packaging contains inner packagings. For example, the UN specification marking for a combination 4G box tested with inner packaging should look like below.

In this case the UN packaging referenced above was tested with liquids inside of plastic bottles which go inside of an outer 4G box.

Now on the other hand, if a single packaging such as a stand-alone drum is tested with solids, it will also have an “S” in the UN marking. In the example below, you have an open head steel drum that was UN tested with solid material. In this case you will also see a max gross weight in KG in the marking instead of a maximum specific gravity and the hydrostatic pressure test result that is required for single packagings tested with liquids.

I suppose it is also possible that a drum can be UN tested with inner containers inside as a combination packaging, and that would also have an “S” in the UN marking. But the only way to be sure is to see the UN test certificate and closing instructions.

Do you have questions about UN Packaging? Take a look at our UN Packaging FAQ or contact our team of experts at 855.734.5469 or send us an email, we’re happy to help.

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Michael Zendano

Michael Zendano started with ICC Compliance Center back in 2016 with several years in the packaging field as a Quality Control Manager. In addition, he has 8 years experience in teaching. Michael works at the Niagara Falls Office as the Regulatory Packaging Expert where he manages packaging projects and procedures and is a member of the Institute of Packaging Professionals (IOPP) and The Chemical Packaging Committee (CPC) . Degrees: M.S. Science of Education.

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