The UN N.4 self-heating test after 42-24: why passing no longer exempts charcoal

By Mohamad Sinno, Charcoal Expert · Last updated 23 July 2026

Since 1 January 2026, a passed N.4 test no longer exempts charcoal

A passed UN N.4 self-heating test no longer exempts charcoal (UN 1361) from dangerous-goods classification at sea. IMDG Amendment 42-24 — voluntary from 1 January 2025, mandatory since 1 January 2026 — removed the SP 925 test-out and replaced it with Special Provision 978.

Adopted by IMO Resolution MSC.556(108) on 23 May 2024, 42-24 also removed SP 223; SP 978's operative line — reproduced in the CINS Charcoal Guidance (September 2024) — says the test "shall not be used to exempt" UN 1361. Behind the change: at least 68 charcoal container-ship fires in 2015–2022 (CINS's incomplete count). The test's story is one piece of how charcoal is classified under UN 1361 and IMDG 42-24 — Class 4.2 and SP 978 live on the hub. Form changes nothing: briquettes made to burn stay UN 1361 (Biochar Europe, September 2025).

What the N.4 test is: the §33.4.6 self-heating oven test

Test N.4 is the UN Manual of Tests and Criteria §33.4.6 method for self-heating substances: a sample is oven-tested, and a "pass" was only ever a classification result for the tested material — a lab datum, not a credential. The scale blind spot ended the test-out: per BSU Report 15/19 (2020, testing by BAM), coconut charcoal passed as a 10 cm cube at 140 °C yet self-ignites below 50 °C at a realistic 27 m³ volume — kinetics the test never sees. A self-heating test certificate only ever recorded that: one sample, one oven.

The teardown: the pre-2026 'exempt' document set vs today's Code

The document set that shipped charcoal as general cargo before 2026 — an accredited-lab N.4 test report, an MSDS declaring "not classified as dangerous goods", and a non-DG booking — fails a 2026 sea booking at every step; none of the three has exemption force. SP 925's test-out era excepted three categories — mineral carbon blacks, N.4-passing consignments, steam-activation carbons (PHMSA's February 2026 description). What replaced it is not another test but the conditions Special Provision 978 sets for carriage — 14-day weathering, packing temperature and documentation. Piece by piece:

Coco Reina books the third column: its coconut shell charcoal briquettes ship declared as UN 1361, Class 4.2, Packing Group III.

The stale-claim check: verifying a supplier's DG story in 2026

A supplier's 2026 DG story checks out on paperwork, not marketing — stale supplier claims, and the lab test reports behind them, outlive their rule. Five asks:

• Dangerous goods declaration showing UN 1361, Class 4.2, plus the packing group.
• Weathering statement with production and packing dates.
• Packing-day temperature record.
• An SDS Section 14 matching the declaration — not "not classified as dangerous goods".
• Treat "exempt", "non-DG", "DG-free" or "UN 1361 certified" as red flags — a self-heating test certificate of any year proves classification, not exemption; the phrase names a transport classification, not a credential — see why "UN 1361 certified" doesn't exist.

Coco Reina's own numbers: a 14-day post-production weathering hold; 20–30 °C measured each stuffing day (limit ≤40 °C); declared UN 1361, Class 4.2, PG III. DG document pack: WhatsApp +628213924038.

What the N.4 test is still useful for

The N.4 test still matters as classification evidence — but for UN 1361 at sea it now informs how the cargo ships as dangerous goods, never whether it is dangerous goods. With the exemption removed, untested material takes at least packing group III under SP 978 (CINS, September 2024); II versus III for tested material is a separate question — the current role of test data.

US domestic rules would keep the test-out — the sea leg does not

No — the US proposal changes nothing at sea: PHMSA's HM-215R (91 FR 5996, 10 February 2026) proposes not to incorporate the 42-24 carbon changes — 49 CFR 173.124 currently requires UN Test N.4 for classification — citing consumer-product burden and a "lack of domestic incidents". The notice describes the sea rule it declines to copy: SP 978 "specifically prohibits the use of the UN N.4 test to except carbon from the IMDG Code". The ocean leg is IMDG-governed, so charcoal bound for a US port still sails as UN 1361, Class 4.2. HM-215R remains a proposed rule — comments closed 13 April 2026; not final as of July 2026.

What the 2026 change does not mean

• Not a ban — charcoal still ships routinely as declared DG under SP 978's conditions.
• Not a quality verdict — Class 4.2 describes transit behaviour, not a batch defect.
• Not a retroactive invalidation — labs still run §33.4.6 tests for classification.
• Not the end of the test elsewhere — US retention is proposed; UN 1362 has its own provisions.

N.4 test FAQ

This page is general information on the transport classification of charcoal, not legal or dangerous-goods advice. Confirm current IMDG requirements with your carrier or a licensed dangerous-goods specialist before shipping.