The code string, character by character

People see the long UN marking on the side of a tote and their eyes glaze over. It looks like a license plate from another planet. But every character is there for a reason, and once you can read it, you can tell at a glance whether a container is legal to fill with a given product and ship on the road. This is the string that carriers and inspectors care about most, so let me decode it piece by piece.

Where the Marking Lives and Why It Is Regulated

The UN marking appears on the data plate attached to the cage, and it must remain durable and legible for the life of the container. It is not marketing. It is a certification, backed by the UN Recommendations on the Transport of Dangerous Goods and mirrored in the US by the Department of Transportation regulations. When you ship a regulated liquid, this marking is the proof that the packaging passed design-type testing. If it is worn away, the tote cannot legally carry dangerous goods, full stop.

The marking is a promise: this exact design was drop-tested, stacked, pressure-tested, and passed. Erase the promise and you erase the approval.

The Packaging Symbol

The string opens with either the circled UN symbol or the letters UN inside a circle. That symbol certifies the container meets United Nations design standards. Everything after it is meaningless without it. If a plate shows the codes but not the UN symbol, treat the marking as unverified.

The Design Type Code: 31HA1

The heart of the marking is the design type code. For a standard caged tote you will typically see 31HA1. Break it apart:

• 31: An IBC for liquids. The leading 3 means liquid; if it were 11 or 21, it would be a solids IBC filled by gravity or under pressure.
• H: The inner receptacle is rigid plastic, the HDPE bottle.
• A: The outer packaging is steel, the tubular cage. Together HA is the plastic-in-steel composite that defines the caged tote.
• 1: A category digit related to the design and pressure rating.

This is the single most useful chunk. It tells you the tote is a liquid-rated composite IBC, which is what almost everything in our used tote inventory is.

The Packing Group Letter

Next comes a letter, X, Y, or Z, that states the hazard range the container is approved for. This mirrors what we cover in our data plate article, but it is worth repeating because it is the field people misread most often.

• X: Approved for packing groups I, II, and III. The most capable rating.
• Y: Approved for packing groups II and III.
• Z: Approved for packing group III only.

Remember the direction: an X-rated tote can legally carry any product a Y or Z tote can, but not the reverse. Match the letter to your product's assigned packing group, which you find on its safety data sheet. Our grades reference maps these letters to the totes we stock.

Density, Test Pressure, and the Testing Year

After the packing group, the marking continues with several technical values:

• The relative density the tote was tested to, for liquids, or the maximum gross mass in kilograms for solids. If your product is denser than the tested density, the tote is not rated for it even if it physically fits.
• The test pressure in kilopascals, from the leakproofness test. For liquids this confirms the container held pressure without leaking.
• The year of manufacture, given as two digits. Combined with the month shown elsewhere on the plate, this starts the service-life clock. Composite IBCs generally cannot be filled with dangerous goods beyond a set number of years from manufacture.

These fields are why two totes that look identical are not interchangeable. One may be tested to a higher density and pressure than the other.

Country Code and Maker's Identity

The tail of the marking carries a state authorization code, the letters identifying the country that authorized the marking, such as USA, followed by a code or name identifying the manufacturer and the design type approval. This is what lets an inspector trace the container back to its certified design. It also helps us verify authenticity when we bring totes in through our buyback program; a marking that does not trace cleanly gets pulled from regulated service.

Reading a Full String in Practice

Put it together and a real marking reads like a sentence once you know the grammar: UN symbol, then 31HA1 for a liquid composite IBC, then Y for packing groups II and III, then the tested density, then the test pressure in kPa, then the year, then USA and the maker code. Here is the workflow I use in the yard:

• Confirm the UN symbol is present and legible.
• Read the design code and confirm it is a liquid composite IBC.
• Check the packing group letter against your product's packing group.
• Confirm the tested density meets or exceeds your product's density.
• Check the year against the service-life limit for your intended use.

If all five clear, the tote is certified for your job. If any are worn or fall short, the container may still be excellent for non-regulated uses like agricultural water or rinse storage, but not for dangerous goods. When you are matching a marking to a specific hazmat shipment and want it confirmed, send us a photo of the plate through the contact page and we will decode it with you.