Class 3

IMDG Class 3 is the hazard class for flammable liquids, substances that emit flammable vapour at or below 60 degrees Celsius. The class covers a wide and commercially significant range of Chinese chemical exports: methanol, ethanol, acetone, methyl ethyl ketone, isopropyl alcohol, n-hexane, toluene, xylene, ethyl acetate, butyl acetate, and dozens more. Class 3 cargo is subject to a packing group assignment that determines packaging strength, container quantity limits, and segregation requirements at sea.

What defines Class 3

A liquid is Class 3 if its closed-cup flash point is 60°C or below. Some liquids with higher flash points are also assigned to Class 3 if their initial boiling point is at or below 35°C. The class therefore captures both routinely-flammable solvents (like ethanol, FP 13°C) and lower-volatility liquids that still pose a vessel fire risk at warm-cargo-deck temperatures.

The packing group split for Class 3 is determined by flash point and initial boiling point:

PG I substances include diethyl ether, carbon disulfide, and acetaldehyde. PG II is the bulk of the routine solvent trade, methanol (UN 1230), acetone (UN 1090), n-hexane (UN 1208), toluene (UN 1294). PG III covers higher-flash-point liquids like xylene (UN 1307), turpentine (UN 1299), and many naphthas.

Common Class 3 chemicals exported from China

The class is a workhorse of the Chinese chemical export trade. Volumes from major load ports (Shanghai, Ningbo, Tianjin, Qingdao) include:

• Methanol (UN 1230, PG II), methanol-to-olefin chain, fuel additive, formaldehyde feedstock
• Acetone (UN 1090, PG II), solvent for paints, coatings, electronics
• Ethanol (UN 1170, PG II), industrial alcohol, sometimes denatured
• Isopropyl alcohol (UN 1219, PG II), semiconductor cleaning, pharmaceutical solvent
• n-Hexane (UN 1208, PG II), extraction solvent for vegetable oils, polymerisation
• Toluene (UN 1294, PG II), paint thinners, TDI feedstock
• Xylene (UN 1307, PG III), paint and ink solvent
• Methyl ethyl ketone (UN 1193, PG II), coating and adhesive solvent
• Ethyl acetate (UN 1173, PG II), flexible packaging adhesive solvent

Packaging requirements

Class 3 cargo must ship in UN-certified packaging matching the assigned packing group. The packaging marking on every drum or IBC reads: UN code (e.g. 1A1 for steel drum, non-removable head; 31HA1 for metal-frame composite IBC), packing group letter (X for PG I, Y for PG II, Z for PG III), test gross mass or specific gravity, year of manufacture, country code, and manufacturer ID.

For methanol shipping in 200kg steel drums: the marking would read something like UN 1A1/Y1.4/200/26/CN/.... UN code, PG II rating (Y), specific gravity rating, capacity in litres, year 2026, China origin. A drum without correct UN marking fails the DG declaration and the cargo will not be accepted by the carrier.

Segregation at sea

Class 3 has specific segregation requirements against other classes when stowed on the same vessel. The IMDG segregation matrix says Class 3 must be stowed:

• “Separated from” Class 1 (explosives), Class 5.1 (oxidisers), Class 5.2 (organic peroxides), and Class 7 (radioactives)
• “Away from” Class 4.1 (flammable solids), Class 4.3 (dangerous when wet)
• “Segregated longitudinally” from Class 1.4 ammunition

For full container loads of a single Class 3 substance the segregation question is usually carrier-managed. For mixed-DG consolidations or LCL the consignee must work with the forwarder to make sure stowage is compatible. See segregation table for the full 9×9 matrix.

Documentation chain

Every Class 3 shipment from China requires:

1. DG declaration by the shipper, listing UN number, proper shipping name, class, packing group, and quantity per package
2. MSDS / SDS in the destination jurisdiction’s required format (SDS section 14 carries the transport classification)
3. UN-certified packaging with the correct marking
4. Container labels and placards, the orange diamond Class 3 placard on each side of the container, plus the UN number marking
5. Bill of lading declaring the cargo as DG with the correct UN number

A Class 3 declaration error, wrong UN number, wrong PG, missing flash point on the SDS, gets the cargo held at the load terminal in China, the destination terminal, or both. The carrier may also fine the shipper for misdeclaration. Misdeclared DG fines from major carriers run USD 5,000 to USD 30,000 per container.

Operator note: methanol and the ChinaPort declaration trap

For methanol shipping out of major Chinese ports under the new ChinaPort DG e-declaration system, the SDS uploaded to the system must show the closed-cup flash point and the UN 1230 designation explicitly. Older Chinese GB/T format SDSs sometimes omit the closed-cup specification or show the open-cup value. If the system rejects the upload, the cargo cannot be loaded. The fix is to insist the factory’s SDS uses the closed-cup measurement before the cargo dispatches inland. Chasing this at the port costs a missed sailing and a reposition booking.

ISO tank builds for Class 3

Most Class 3 PG II flammables ride T11 stainless (the global workhorse) under the IMDG 4.2.5.2.5 substitution rule. Lower-pressure PG III cargoes (diesel, jet fuel, kerosene UN 1202 / 1863 / 1223) can ride T3 stainless. Higher-vapour-pressure Class 3 cargoes that exceed the T11 envelope ride T15 or T18 (10 bar test pressure). PG I flammables not authorised in T11 ride T14. The ISO Tank Loading Calculator computes max loadable mass for any tank build under the IMDG fill rules.

Related terms

IMDG is the umbrella code. UN number identifies the specific substance. Packing group classifies the hazard severity. Marine pollutant is a parallel designation that can apply alongside the Class 3 label. Segregation table lays out which classes can stow with which.