IMDG 42-24 Segregation Rules: New Lithium Stowage Categories Effective 2026

If you ship lithium batteries, vehicles with batteries inside, or any IMDG Class 9 dangerous goods through a U.S. ocean port, January 1, 2026 was the day the rules changed. IMDG Code Amendment 42-24 — adopted in May 2024 by IMO Resolution MSC.556(108) — became mandatory worldwide, replacing the transitional Amendment 41-22 period.

The full amendment runs to hundreds of pages of text. For most freight forwarders, customs brokers, and exporters out of South Florida, three changes do the practical work: revised stowage categories for lithium batteries, tightened criteria under Special Provision 188, and the introduction of UN 3556, UN 3557, and UN 3558 for battery-powered vehicles.

What “mandatory” means for U.S. shippers

During 2025, shippers could file dangerous goods declarations against either Amendment 41-22 or 42-24, as long as they applied one consistently to each shipment. As of January 1, 2026, only Amendment 42-24 is valid for new bookings. Carriers, terminals, and Coast Guard inspectors are checking against the new edition.

A DG declaration referencing Amendment 41-22 today will be rejected at the terminal. That is the practical compliance test.

Lithium battery stowage — what changed

The biggest functional change is in the segregation and stowage tables for lithium battery cargo.

Watt-hour-based stowage categories. Amendment 42-24 revises the stowage category assignments for several lithium battery UN numbers based on watt-hour thresholds. The intent is to align stowage risk more precisely with battery energy — a 100 Wh cell is not the same hazard as a 500 Wh cell, and the rules now reflect that.

SP 188 tightening. Special Provision 188 covers smaller lithium batteries that can be shipped under reduced-regulation conditions. Amendment 42-24 tightens the criteria — packaging requirements, marking, and shipping limits — under which a battery shipment qualifies for SP 188. Some shipments that cleared SP 188 under 41-22 will need full Class 9 documentation under 42-24.

New UN numbers for battery-powered vehicles. This is the change most likely to trip up shippers who do not read amendment notes:

• UN 3556 — Vehicle, lithium-ion battery-powered
• UN 3557 — Vehicle, lithium-metal battery-powered
• UN 3558 — Vehicle, sodium-ion battery-powered

Previously, vehicles with installed batteries were typically declared under UN 3171. Under 42-24, the more specific UN numbers apply to lithium-ion, lithium-metal, and sodium-ion-powered vehicles. Sodium-ion in particular is new — it was not a recognized UN-numbered class for vehicles until this amendment.

How IMDG segregation actually works

The segregation framework lives in Chapter 7.2.4 of the IMDG Code. It cross-references 14 segregation groups to produce a required separation term for any combination of cargoes on the same vessel:

1. “Away from” — separated, but in the same compartment is acceptable
2. “Separated from” — different compartments or holds, or vertically separated with a deck
3. “Separated by a complete compartment or hold from” — full compartment between
4. “Separated longitudinally by an intervening complete compartment or hold from” — strongest separation

When you book a lithium battery container alongside other DG, the carrier’s planning software runs this matrix to confirm stowage is legal. Get the UN number wrong on the booking and your container can end up rejected at the load port — or worse, loaded into a non-compliant stowage position and held at the discharge port.

What this means at the booking stage

Three practical items for shippers and their freight forwarders:

Re-check your MSDS and DG paperwork. Templates created against Amendment 41-22 may have the wrong UN number, the wrong packing instruction, or an SP 188 reference that no longer applies. Audit your top SKUs first.

Update training records. IMDG-certified personnel need refresher training that covers the 42-24 changes. Carriers and terminals do verify training currency during DG audits.

Coordinate early with your NVOCC or VOCC. If you are a regular DG shipper, your carrier’s DG desk has internal guidance documents on 42-24 stowage planning. Use them — they are typically more current than third-party summaries.

Common 42-24 errors at Miami and Port Everglades

In the first six months of mandatory 42-24, the rejections we have seen at South Florida terminals cluster around:

• Battery-powered ride-on equipment (forklifts, golf carts, e-bikes) booked under UN 3171 instead of UN 3556 or UN 3557
• SP 188 declarations on lithium battery shipments that now fall above the revised energy thresholds
• Outdated stowage requests on the booking that do not match the new compartment requirements
• Sodium-ion battery shipments — increasingly common — booked under generic UN numbers because the shipper or forwarder did not realize UN 3558 now exists

Each of these is fixable at booking. None is fixable easily after the container is gated in.

How Go Freight handles IMDG shipments

Go Freight’s mobile hazardous materials compliance team works alongside Florida shippers on both IATA and IMDG dangerous goods documentation. We catch outdated UN number references, verify packing instructions against the current IMDG edition, and coordinate with VOCC DG desks at PortMiami and Port Everglades on stowage planning before the booking is closed.

If you are shipping batteries, battery-powered vehicles, or any Class 1-9 dangerous goods through South Florida and want a DG-trained partner reading the rules with you, call Go Freight at (786) 244-3235 or visit our home page to start the conversation about hazardous materials compliance.

Sources: IMDG Code Amendment 42-24 — TT Club; IMDG Code Amendment 42-24 Mandatory from 1 January 2026 — Kerry Logistics; What is New in IMDG 42-24 — ICC Compliance Center; IMO Resolution MSC.556(108).