IMDG Sea Transport

IMDG is the International Maritime Dangerous Goods Code used for sea transport. Compared to air shipment, sea shipment often has fewer operational constraints, but it is still dangerous goods–driven and document-heavy. The most common failure mode is not the ocean crossing. It is incorrect classification, packaging, or documentation that causes port holds and carrier refusal.

How IMDG fits into the global transport stack

Layer	What it is	Why it matters
UN transport framework	Global model approach for dangerous goods	IMDG aligns to UN model regulations and classification logic
UN 38.3	Transport tests for lithium cells and batteries	Sea acceptance typically expects UN 38.3 evidence on request
IMDG Code	Maritime dangerous goods code used by most carriers and ports	Defines packaging, segregation, marking, documentation, and stowage principles

What IMDG governs for batteries

Dangerous goods classification and shipping name selection for lithium cells and batteries.
Packaging requirements and packing instructions appropriate for sea transport.
Marking and labeling requirements used by carriers and port authorities.
Dangerous goods documentation and carrier acceptance workflows.
Stowage and segregation principles on vessels and in port handling.

Sea shipment vs air shipment: what changes

Topic	Sea transport (IMDG)	Practical implication
Carrier acceptance	Often more permissive than air, but still strict on documentation and packaging	Port holds and rollovers happen when paperwork is wrong
Quantity and SOC constraints	Typically less restrictive than air, but carrier rules can add constraints	Do not assume relief; confirm carrier acceptance rules per lane
Stowage and segregation	Important due to vessel fire scenarios and container stacking	Your declared classification and packaging affect stowage decisions
Damaged or defective batteries	Often restricted; may require special conditions, approvals, and packaging	Treat DDR as a separate shipment class and avoid surprises at port

Core controls for IMDG compliance

Control area	What to do	Evidence to retain
Classification decision record	Define how you classify each shipment type: cells, batteries, with equipment, in equipment, DDR, waste returns	Signed decision record with triggers and assumptions
UN 38.3 test evidence	Control test reports and test summaries at the model/revision level	Test summary tied to revision and change control
Packaging specifications	Bind packaging to the declared packing instruction; control materials and configuration	Packaging spec, work instruction, training sign-offs
Marking and labeling	Use controlled label sets and ensure they match the declared class and configuration	Label checklist and photos for representative shipments
Documentation package	Standardize dangerous goods documents and retain copies per shipment	Completed DG docs, carrier acceptance confirmations
Lane and carrier rules	Maintain a carrier acceptance matrix per lane (what each carrier will and will not take)	Acceptance matrix with last-verified date and owner

Common sea shipment gotchas

Container consolidation with incompatible cargo causes segregation issues and rework.
Documentation mismatches between shipper, forwarder, and carrier delay loading and trigger holds.
Battery condition is unclear (DDR risk); port or carrier refuses once discovered.
Packaging spec used for air is applied to sea without checking IMDG packing instruction fit.
Returns and end-of-life shipments drift into “waste shipment” territory without the right controls.

Special case: returns, end-of-life, and waste shipments by sea

Sea lanes are commonly used for returns and end-of-life movements. That creates a boundary between dangerous goods shipment rules and waste shipment controls. If the shipment is declared or treated as waste, additional rules may apply including consent and downstream treatment evidence. Treat end-of-life sea movements as compliance events, not logistics tasks.

Minimum compliance artifacts to control

Artifact	What it proves	Owner
UN 38.3 test summary	Transport test basis for the model and revision	Compliance, Engineering
Classification decision record	Correct shipping configuration selection	Compliance, Logistics
Packaging and labeling instruction	Packaging and labels conform to IMDG expectations	Logistics, Operations
Dangerous goods documents	Required declarations and shipment documentation	Logistics, Forwarder
Carrier acceptance confirmation	That your carrier accepts your battery class on that lane	Logistics

Where to go next

Topic	Recommended page	Why
UN 38.3 testing and evidence control	UN 38.3 transportation testing	Test summary controls and revision pitfalls
Air, sea, land transport hub	Transport compliance hub	Navigation to IATA and ADR pages
Cross-border waste shipments	Cross-border waste shipments	When end-of-life movements become waste-controlled shipments
BESS handling and safety	BESS-Guide.com	System-level safety, DDR handling, and incident risk factors

Disclaimer. Informational guidance only. Not legal advice. Sea transport compliance depends on correct classification, packaging, labeling, documentation, and carrier acceptance. Confirm obligations using the current IMDG Code and qualified dangerous goods professionals.