Size guide · R-04
UN markings
decoded.
Short answer
- Hazmat service life: 5 years from the moulding year
- Leakproofness retest required at 2.5 years
- X = PG I–III, Y = PG II–III, Z = PG III only
- Non-regulated liquid needs no valid marking at all
Send us a plate photo
Character by character
The eight segments
The United Nations packaging symbol. Everything after it is a certified specification, not marketing.
Category and construction: 31 = composite IBC for liquids. 11 = rigid for solids, 21 = rigid for solids under pressure.
Inner receptacle material: H = plastic. A = steel, B = aluminium, N = other metal, L = textile, M = paper, G = fibreboard.
Outer packaging: A = steel, 1 = with structural equipment (the cage). A2 would be steel without.
Packing group authorisation: Y covers PG II and III. X covers I, II and III. Z covers PG III only.
Hydrostatic test pressure in kPa, or stacking load in kg depending on position — read against the rest of the string.
Year of manufacture (2026). Composite IBCs for hazmat have a 5-year service life from this date, re-testable at 2.5 years.
Country of certification and the manufacturer or reconditioner registration code.
Reference tables
Every code you might meet on a plate
Category — the first two digits
| Code | Type | Contents |
|---|---|---|
| 11 | Rigid IBC | Solids, discharged by gravity |
| 13 | Flexible IBC | Solids (big bags / FIBCs) |
| 21 | Rigid IBC | Solids, discharged under pressure |
| 31 | Composite IBC | Liquids — the common caged tote |
Inner receptacle material — the letter
| Letter | Material |
|---|---|
| A | Steel |
| B | Aluminium |
| N | Metal other than steel or aluminium |
| H | Plastic — HDPE on virtually every composite tote |
| L | Textile |
| M | Paper, multiwall |
| G | Fibreboard |
Outer packaging and structural equipment
| Code | Meaning |
|---|---|
| A1 | Steel outer, with structural equipment — the cage carries load |
| A2 | Steel outer, without structural equipment |
| B1 / B2 | Aluminium outer, with / without structural equipment |
| H1 / H2 | Plastic outer, with / without structural equipment |
| D1 / D2 | Plywood outer |
| G1 / G2 | Fibreboard outer |
Packing group authorisation
| Letter | Authorised for | Typical materials |
|---|---|---|
| X | Packing groups I, II and III | High-hazard liquids |
| Y | Packing groups II and III | Medium and low hazard — most common on IBCs |
| Z | Packing group III only | Low hazard |
Worked examples
Three plates, read out loud
UN 31HA1/Y/0624/USA/M5521
Composite IBC for liquids, plastic inner, load-bearing steel cage, authorised for packing groups II and III, manufactured June 2024 in the USA by maker code M5521. In hazmat service until June 2029, with a leakproofness retest due December 2026.
UN 31HA1/Y/1120/21/USA/R2208
Same construction and packing groups. Test pressure 1,120 kPa segment present, manufactured 2021, and the R prefix on the code indicates a reconditioner rather than an original manufacturer. Service life ended in 2026 — this unit is out of hazmat service permanently, and is fine for non-regulated liquid.
UN 31HA2/Z/0319/USA/M1180
Composite IBC, plastic inner, steel outer WITHOUT structural equipment, so it must not be stacked. Packing group III only. Manufactured March 2019 and therefore long out of hazmat service. Unusual construction, and worth a second look before anyone racks it.
Short answer
- Service life is absolute — no test extends it
- An out-of-life IBC is still legal for non-regulated liquid
- Reconditioner codes usually carry an R prefix
- If the plate is illegible, the container is not certified
Questions
Marking questions
What does UN31HA1 mean?
31 = composite IBC for liquids; H = plastic inner receptacle; A = steel outer packaging; 1 = with structural equipment, meaning the cage carries load. Together: a plastic bottle inside a load-bearing steel cage, certified for liquids. It is by far the most common marking on a 275 or 330 gallon tote.
What does the Y mean in a UN marking?
Packing group authorisation. Y covers packing groups II and III. X covers I, II and III. Z covers only III. A Y-marked IBC cannot legally carry a packing-group-I material regardless of how sound the container is.
How do I find the manufacture date?
Two digits in the marking string give the year. On a composite IBC for hazmat that date starts a five-year service clock, with a leakproofness retest required at 2.5 years. Many plates also carry a month, and some manufacturers mould the date into the bottle itself near the top shoulder.
What is the difference between 31HA1 and 31HA2?
The final digit describes structural equipment. A1 means the steel outer packaging provides structural support — the cage carries the stacking load. A2 means it does not. In practice almost every caged composite tote you will meet is A1.
Does a non-hazmat tote need a UN marking?
No. If you are storing water, dust-control solution or non-regulated industrial liquid, the marking is irrelevant and an unmarked or out-of-life container is perfectly legal and usually cheaper. The marking only governs regulated transport.
Where to look
Finding the marking in the first place
Half the questions we get about UN markings are really questions about where the plate is and why it is unreadable.
| Location | What you find there | Notes |
|---|---|---|
| Riveted plate on a cage upright | Full marking string, maker, dates | The authoritative source |
| Second plate on the opposite upright | Duplicate, or reconditioner re-marking | Check both — they can disagree |
| Moulded into the bottle shoulder | Manufacturer and moulding date | Survives when the plate does not |
| Printed label on the cage | Often a filler’s label, not a UN marking | Not a certification |
| Stamped into a base rail | Occasionally the maker code | Rarely a full string |
When a plate is corroded or painted over, the moulded date on the bottle shoulder tells you the age even though it does not restore certification. An illegible plate means the container is not certified for regulated transport, and nothing short of full re-testing and re-marking changes that.
Common confusions
Six things the marking does not mean
Collected from questions we answer repeatedly. Each of these is a reasonable assumption and each one is wrong.
| People assume | Actually | Consequence of the mistake |
|---|---|---|
| A UN marking means it is currently certified | It means it was certified when made | Shipping on an out-of-life container |
| Retesting extends the service life | The five-year life is absolute | Planning a fleet around units that expire |
| Y covers everything hazardous | Y covers packing groups II and III only | Carrying a PG I material illegally |
| The test pressure is the working pressure | It is a test figure, not an operating rating | Pressurising an atmospheric vessel |
| All composite totes are 31HA1 | A2 exists and must not be stacked | Stacking a non-load-bearing cage |
| Non-hazmat liquid needs a valid marking | It does not; the marking governs regulated transport only | Paying for certification you do not need |
Short answer
- Read the two-digit year and count five
- X covers PG I–III, Y covers II–III, Z covers III only
- An illegible plate means uncertified, full stop
- Water and non-regulated liquid need no valid marking at all
From the Yard Journal
Longer pieces from the people who run the wash line, the test bay and the trading desk.
12 June 2025 · 3 min
What changed when we got our own reconditioner code
Before 2023 a UN re-marking took three weeks in somebody else's queue. Now it takes four days in ours. The interesting part is what the delay was actually costing.
Priya Raghunathan · Head of reconditioning
Read14 September 2023 · 4 min
What the 2.5-year retest actually catches
Three years of test bay records, sorted by failure mode. The periodic leakproofness test is not a formality, and what it finds is not what most people expect.
Priya Raghunathan · Head of reconditioning
Read
Next move
Photograph your plates and send them over.
Phone photos are fine. We will decode the strings, build a periodic schedule and flag which of your units quietly left hazmat service last year — which, in most fleets we audit, is several.