IMDG Class 6.1 is the hazard subclass for toxic substances, those that can cause death, serious injury, or harm to human health on swallowing, inhalation, or skin contact. The class spans inorganic toxics (cyanides, arsenic and mercury compounds), agrochemicals (many active pesticides and herbicides), and industrial intermediates (isocyanates, phenols, anilines). Volume-wise the class is dominated in Chinese-export trade by isocyanates and substituted aromatics.
What defines Class 6.1
The PG assignment is based on three toxicity routes, oral, dermal, and inhalation, using LD50 and LC50 values. The most stringent route determines the PG.
| Packing group | Oral LD50 (mg/kg) | Dermal LD50 (mg/kg) | Inhalation LC50 (dust/mist, mg/L) |
|---|---|---|---|
| PG I | ≤ 5.0 | ≤ 50 | ≤ 0.2 |
| PG II | > 5.0 to ≤ 50 | > 50 to ≤ 200 | > 0.2 to ≤ 2 |
| PG III | > 50 to ≤ 300 | > 200 to ≤ 1000 | > 2 to ≤ 4 |
PG I substances include sodium cyanide (UN 1689), arsenic trioxide (UN 1561), and many organophosphate pesticides. PG II includes phenol (UN 1671), aniline (UN 1547), and TDI (UN 2078). PG III includes most lower-toxicity industrial intermediates.
Common Class 6.1 chemicals exported from China
China is a major exporter of several Class 6.1 substances:
- Toluene diisocyanate (TDI, UN 2078, PG II), polyurethane foam manufacturing. Wanhua Chemical and other Chinese producers dominate global supply.
- Methylene diphenyl diisocyanate (MDI, UN 2489, PG III as solid; UN 3082 as marine pollutant solution), polyurethane elastomers, insulation foam. Wanhua again is a global top-three producer.
- Phenol (UN 1671, PG II as solid; UN 2821 as solution), phenolic resin, plasticiser, BPA feedstock
- Aniline (UN 1547, PG II). MDI feedstock, dye and pesticide intermediate
- Sodium cyanide (UN 1689, PG I), gold mining extraction (precious-metal recovery), electroplating
For TDI and MDI especially, every Western polyurethane manufacturer has a Chinese supply line in their book. The Class 6.1 designation drives the entire transport, packaging, and destination clearance regime for these cargoes.
Packaging requirements
Class 6.1 packaging must be UN-certified to the assigned PG. PG I substances ship in steel drums or rigid IBCs with secondary containment. PG II substances like TDI ship in steel drums (200kg or 220kg) or in stainless-steel ISO tanks (the bulk-shipping mode for volume buyers). PG III substances can use HDPE drums or fibreboard boxes with inner packaging.
For TDI specifically the standard packaging modes are 220kg steel drums (UN 1A1/X) for parcel orders or 20-foot ISO tanks holding ~18 tonnes for bulk buyers. The drum-vs-ISO economics depend on annual volume, break-even is typically around 300 tonnes per year per destination.
Destination customs scrutiny
Class 6.1 cargo attracts more destination customs scrutiny than most DG classes. Three routine triggers:
- TSCA inventory check at US ports. US Customs cross-references the substance against the TSCA inventory and the Section 5 PMN list. A 6.1 substance not on TSCA active inventory triggers a documentation hold.
- REACH SVHC check at EU ports. Many Class 6.1 substances are on the REACH SVHC candidate list. Cargo can clear, but the buyer must produce SVHC declarations within 45 days. Missing this triggers ECHA enforcement.
- AICIS check at Australian ports. Cargo of toxic substances new to AICIS (the Australian inventory) can be held pending registration.
The lesson: Class 6.1 cargo from China requires a clean regulatory paper trail at destination. Confirm registration status before booking, not at the port.
Marine pollutant designation
Many Class 6.1 substances are also designated as marine pollutants under MARPOL Annex III. The marine pollutant flag triggers additional packaging marking (the “fish and tree” symbol) and specific stowage requirements (cannot stow on top of cargo without secondary containment). Always check the MARPOL designation on the SDS section 14, many substances are dual-classified Class 6.1 and marine pollutant.
Operator note: TDI ISO-tank repositioning
For volume TDI buyers using ISO tanks, the freight economics are dominated by tank repositioning, not the substance itself. A laden ISO tank from Shanghai to Houston is straightforward; the empty repositioning back to China is typically negotiated as a discounted backhaul slot. If the carrier cannot find a backhaul (low-utilisation period), the round-trip equivalent rate applies and your effective freight per tonne climbs. Build a quarterly review of round-trip vs one-way ISO economics into the supply contract, the difference can be USD 300 to USD 600 per tonne on a major chemical lane.
ISO tank builds for Class 6.1
Class 6.1 PG II toxics typically ride T11 stainless (~1,000 UN cargoes including TDI UN 2078 and a wide range of toxic-liquid intermediates). PG I toxics escalate to T14 stainless (no bottom outlet, frangible disc plus tell-tale gauge). Hazard Zone A and B toxics-by-inhalation require T22 (10 mm reference shell, ASME U-stamp mandatory under 49 CFR 178.275). Highest-hazard pyrophorics like methyl iodide UN 2644 ride T21. The ISO Tank Loading Calculator applies the IMDG 4.2.1.9 fill rules.
Related terms
IMDG umbrella code. UN number. Packing group. IMDG Class 6.2 covers infectious substances. Marine pollutant. SDS section 14 carries the transport classification.