If you ship dangerous goods, sooner or later someone will hand back your freight and point at the box. Maybe the mark on the carton doesn’t match the packing group of your product. Maybe there’s no mark at all.
The string of letters and numbers printed on a UN specification package — something like 4G/Y145/S/26/USA/+AB1234 — tells carriers, inspectors, and consignees exactly what that package has been tested to do. Once you know how to read it, you can spot problems before your freight ever reaches the airline or the port.
How to read a UN specification mark
Take the example above and break it apart, left to right:
- 4G — the packaging code. The first number is the container type (4 = box), and the letter is the material (G = fiberboard). So 4G is a fiberboard box.
- Y — the packing group performance level. Y-rated packaging passed tests for Packing Group II and III materials.
- 145 — for combination packagings, the maximum gross mass in kilograms at which the package was tested. For single packagings holding liquids, you’d see a specific gravity value and a hydrostatic test pressure instead.
- S — indicates the package is intended for solids or for inner packagings. Single packagings for liquids show test pressure data in this position.
- 26 — the last two digits of the year of manufacture.
- USA — the country authorizing the mark.
- +AB1234 — the code identifying the manufacturer or approval agency.
Every element matters. A box marked with a Y rating and a 145 kg tested gross mass cannot legally carry a Packing Group I liquid, and it can’t be loaded past its tested weight — even if it physically holds more.
Common package types you’ll see
A few codes cover the vast majority of dangerous goods shipments:
4G — fiberboard box
The workhorse of hazmat shipping. A 4G box is tested as a system: the outer box, the specific inner packagings, cushioning, and closure method used in the test. To ship legally under a standard 4G mark, your packed configuration must match what the manufacturer tested — same inner containers, same count, same arrangement.
1A1 and 1A2 — steel drums
1A1 is a steel drum with a non-removable (tight) head, typically used for liquids. 1A2 has a removable head and is common for solids and for salvage applications. The same logic applies to plastic drums (1H1, 1H2) and jerricans (3H1).
4GV — variation packaging
The “V” is the exception to the tested-system rule. A 4GV box is tested to a more demanding standard that allows you to place varied inner packagings inside — different bottles, cans, or jars — provided you follow the manufacturer’s instructions on cushioning, absorbent material, and maximum inner packaging quantities.
X, Y, and Z: what the packing group letters mean
The performance letter links packaging strength to product danger:
- X — tested for Packing Group I, II, and III (high, medium, and low danger)
- Y — tested for Packing Group II and III
- Z — tested for Packing Group III only
The rule flows in one direction: stronger packaging can carry lower-danger goods, never the reverse. A Z-rated box under a PG II corrosive is a violation waiting to be found — and at an airline acceptance counter, it will be found.
Single vs. combination packaging
A single packaging — a drum or jerrican — is the sole containment for the product. A combination packaging is inner packagings (bottles, cans, bags) inside a tested outer packaging like a 4G box. Most small-quantity commercial shipments, and nearly all air shipments of packaged dangerous goods, use combination packagings, because inner packaging limits under the IATA DGR and 49 CFR are built around them.
Don’t confuse a combination packaging with an overpack, which is simply a means of consolidating already-compliant packages (say, shrink-wrapping four 4G boxes to a pallet) and carries its own marking requirements.
When 4GV packaging is worth the money
4GV boxes cost more than standard 4G boxes. They earn their keep when:
- You ship many different products in varying bottle sizes and can’t stock a tested 4G system for each one.
- You’re repacking damaged or non-compliant freight and need a compliant outer packaging that accepts whatever inner containers survived. Our hazmat repacking team keeps 4GV inventory on hand in Miami for exactly this reason.
- Volume is low. For one-off shipments, a 4GV kit with absorbent and cushioning is usually cheaper than sourcing and validating a dedicated tested configuration.
If you ship the same product in the same bottle by the thousands, a purpose-tested 4G system will almost always be cheaper per unit.
Closure instructions are not optional
This is the compliance point shippers miss most often. Under the Hazardous Materials Regulations, packaging manufacturers must provide written closure instructions, and the shipper must close the package in accordance with those instructions — the correct tape type and pattern, torque values on drum closures, the specified number of fasteners. A perfectly good UN-marked box closed the wrong way is a non-compliant package, full stop.
Keep the closure instructions on file and make sure the people taping boxes and torquing drums have actually seen them. This is a core topic in function-specific hazmat training.
A note for South Florida shippers
Miami sits at the intersection of three demanding acceptance environments: air cargo at MIA, ocean freight through PortMiami and Port Everglades, and a heavy flow of Latin America–bound exports. Airline DG acceptance staff at MIA check UN marks against the declaration line by line, and ocean carriers apply IMDG Code packing requirements just as strictly. If you’re unsure whether your packaging matches your product, a quick hazmat consultation before tender is far cheaper than a rejection after.
Frequently asked questions
What does the 4G mean on a box?
In a UN specification mark, “4” designates a box and “G” designates fiberboard, so 4G means a UN-tested fiberboard box. It must be used as a combination packaging with the inner packagings and closure method specified by the manufacturer, and the rest of the mark (performance letter, gross mass, year, country, manufacturer code) defines its tested limits.
What is the difference between 4G and 4GV packaging?
A standard 4G box is certified only with the specific inner packagings used during testing, so your packed shipment must replicate that tested system. A 4GV “variation” box passes more severe testing and may be used with a variety of inner packagings, provided you follow the manufacturer’s instructions on cushioning, absorbent material, and quantity limits — which makes it ideal for mixed products and repack work.
Can I use X-rated packaging for a Packing Group III material?
Yes. X-rated packaging is tested to the Packing Group I performance level and may be used for PG I, II, or III materials. The reverse is not allowed: Y-rated packaging is limited to PG II and III, and Z-rated packaging may only be used for PG III materials.
