Packaging Technical Library › Hazmat Packaging › IBCs · Document TL-003
An IBC’s UN mark packs the container type, materials, packing group rating, build date, stacking load and gross mass into one line, and its data plate adds the test dates that decide whether it can still be filled. This guide decodes a 31HA1 composite tote, field by field.
Example mark. Read it as: a composite IBC for liquids with a rigid plastic bottle in a steel cage, tested for Packing Group II and III, made February 2026, certified in the USA by registrant M1234, stacking test load 4,800 kg, maximum gross mass 1,200 kg.
Reading the UN mark, field by field
| Field · example | What it means | |
|---|---|---|
| 1 | UN packaging symbolu/n | Certifies that the IBC design passed UN performance tests. |
| 2 | IBC type31 | 11 = solids, loaded and discharged by gravity · 21 = solids, loaded or discharged under pressure over 10 kPa · 31 = liquids. Flexible IBCs (bulk bags) start with 13. |
| 3 | MaterialsHA | For a composite IBC, the first letter is the inner receptacle (H = rigid plastic) and the second is the outer cage or casing (A = steel). See the material table. |
| 4 | Category1 | On a composite IBC: 1 = rigid plastic inner receptacle, 2 = flexible plastic inner. On a rigid plastic IBC: 1 = built to carry a stacking load, 2 = freestanding. |
| 5 | Packing group ratingY | X = PG I, II and III · Y = PG II and III · Z = PG III only. |
| 6 | Month and year02 26 | Month and last two digits of the year of manufacture. For a composite IBC, the inner receptacle carries its own date too. |
| 7 | Country / certifierUSA · M1234 | The authorizing country and the manufacturer’s name or registered symbol. |
| 8 | Stacking test load4800 | The load in kg used in the stacking test. 0 means the IBC is not designed to be stacked. |
| 9 | Maximum gross mass1200 | The highest permitted gross mass in kg: IBC plus contents. |
IBC material letters
| Letter | Material |
|---|---|
A | Steel |
B | Aluminum |
N | Metal other than steel or aluminum |
H | Rigid plastic |
HZ | Composite: plastic inner receptacle; Z is replaced by the outer material letter |
G | Fiberboard |
C / D / F | Natural wood / plywood / reconstituted wood |
L / M | Textile / multiwall paper (flexible IBCs) |
Common codes
Tote: 31HA1 — liquids, rigid plastic bottle, steel cage.
Plastic: 31H2 — liquids, freestanding rigid plastic IBC.
Bulk bag: 13H3 — flexible, woven plastic with liner.
Rules to check before filling
- Plastic has a service life. Rigid plastic and composite IBCs may carry hazmat for 5 years from the inner receptacle’s date of manufacture (49 CFR 173.35, UN Model Regulations 4.1.1).
- 2.5-year test. IBCs for liquids, or for solids loaded or discharged under pressure, need a leakproofness test and external inspection every 2.5 years (49 CFR 180.352).
- 5-year inspection. An internal inspection is due every 5 years. Do not fill an IBC once a test or inspection is overdue.
- Read the data plate. Beyond the UN mark, the plate shows capacity at 20 °C, tare mass, test pressure (liquids), and the dates of the last leakproofness test and inspection.
- Respect stacking. A
0stacking load or a crossed-out stacking symbol means do not stack. - Rebottled totes carry the new inner receptacle’s date. That date, not the cage’s, starts the 5-year clock.
Before you fill: a four-step check
31 type. Gravity-discharged solids can use 11; pressure-discharged solids need 21 or 31.X/Y/Z on the mark.Frequently asked questions
What does 31HA1 mean on an IBC?
31HA1 is a composite IBC for liquids (31) with a rigid plastic inner receptacle (H) inside a steel outer cage (A). The final 1 means the inner receptacle is rigid plastic.
How long can a plastic IBC tote be used for hazardous materials?
Rigid plastic and composite IBCs may be used for hazardous materials for 5 years from the date of manufacture of the inner receptacle, provided the periodic tests are current.
How often do IBCs need to be retested?
Under 49 CFR 180.352, IBCs for liquids, or for solids loaded or discharged under pressure, need a leakproofness test and external inspection every 2.5 years and an internal inspection every 5 years.
What is the difference between 11, 21 and 31 IBCs?
11 is for solids loaded and discharged by gravity, 21 for solids loaded or discharged under pressure over 10 kPa, and 31 for liquids.
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- How to Read UN Packaging Markings (Code Guide) · TL-004
- UN Markings: Open-Head Steel Drums (Solids) · TL-001
- UN Markings: Tight-Head Steel Drums (Liquids) · TL-002
For reference only. This guide explains the marking format and does not replace the regulations or your packaging’s test report. Confirm against 49 CFR 178.700–178.703, 49 CFR 173.35, 49 CFR 180.352 and the UN Recommendations on the Transport of Dangerous Goods, Model Regulations, Chapter 6.5. The mark shown is an example, not a real certification.