IMDG Class 8 is the hazard subclass for corrosive substances, substances that destroy living tissue on contact or severely corrode metal at standardised test rates. The class includes acids (sulphuric, hydrochloric, nitric, phosphoric, formic, acetic), bases (sodium hydroxide, potassium hydroxide, ammonia solutions), and various oxidising acids and salts. By volume Class 8 is the single largest DG class in Chinese chemical exports, caustic soda alone runs millions of tonnes per year out of Chinese ports.
What defines Class 8
A substance is Class 8 if it causes irreversible damage to intact skin in standardised test exposure or corrodes steel or aluminium at a rate above 6.25mm per year at 55°C. The PG split:
| Packing group | Skin destruction time | Steel/aluminium corrosion rate |
|---|---|---|
| PG I | ≤ 3 minutes | n/a (PG I assigned by skin damage) |
| PG II | > 3 minutes to ≤ 60 minutes | n/a |
| PG III | > 60 minutes to ≤ 4 hours, or | > 6.25mm/year at 55°C |
PG I includes oleum (UN 1831, fuming sulphuric acid), nitric acid above 70%, and bromine. PG II includes most concentrated mineral acids and caustic solutions. PG III is the workhorse, solid sodium hydroxide flakes, dilute acid solutions, many corrosive salts.
Common Class 8 chemicals exported from China
The volume tier:
- Caustic soda, sodium hydroxide (UN 1823 solid, PG II; UN 1824 solution, PG II or III), the largest-volume Class 8 export. Pulp and paper, alumina refining, soap and detergent manufacture. Major export from Shandong, Jiangsu, Zhejiang.
- Sulphuric acid (UN 1830, PG II), fertiliser feedstock, battery acid, chemical synthesis. Largest single industrial chemical produced globally.
- Hydrochloric acid (UN 1789, PG II for >25%; PG III for ≤25%), pickling, water treatment, food processing. Transport classification depends on concentration.
- Phosphoric acid (UN 1805, PG III), fertiliser, food acidulant, metal treatment
- Potassium hydroxide (UN 1813 solid, PG II; UN 1814 solution, PG II), biodiesel catalysis, soft soap, alkaline batteries
Bulk vs parcel packaging economics
Class 8 is where the bulk-vs-parcel decision drives most of the buyer’s freight cost. Three modes are routine:
- 25kg or 1MT bags (solid caustic soda flakes / pearls), for buyers consuming under ~200 tonnes per year. Standard for distributor and smaller industrial users.
- 220kg drums (acid solutions, smaller volumes), the standard parcel mode for sulphuric acid, hydrochloric acid, hydrogen peroxide, and similar liquid corrosives.
- 20-foot or 24-foot ISO tanks (volume buyers), for users consuming above ~500 tonnes per year per chemical. ISO tanks for corrosives must be lined or coated appropriately: HDPE-lined for caustic, PFA-lined for hydrofluoric acid, rubber-lined for some sulphuric acid grades.
The economics are stark. Caustic soda flakes in 25kg bags run typically USD 380 to USD 480 per MT FOB Shanghai. The same product in ISO tank bulk runs USD 280 to USD 360 per MT, but the buyer needs ISO-tank reception capability at destination (a permit, a lined storage tank, an unloading pump). The breakeven for switching from bagged to ISO bulk is roughly 300 to 500 tonnes per year per destination.
Packaging requirements
UN-certified packaging matched to the assigned PG. For solid caustic soda flakes: 25kg multi-wall paper bags with PE inner liner, marked UN 13H1 or equivalent for super sacks. For acid solutions in drums: HDPE drums (UN 1H1 or 1H2) for hydrochloric and acetic acid; lined steel drums (UN 1A1) for sulphuric acid (steel resists concentrated sulphuric well). For ISO tanks: T11 or T14 portable tanks with appropriate lining.
The lining choice for ISO tanks is the most common Class 8 packaging issue. A buyer ordering caustic soda solution in an unlined steel ISO tank gets an iron-contaminated cargo that fails their downstream process. Always confirm the lining specification on the booking, the carrier or tank operator should issue a confirmation specifying “HDPE-lined T11” or equivalent.
Segregation at sea
Class 8 must be stowed:
- “Separated from” Class 1 (explosives), Class 4.1 (flammable solids), Class 4.3 (dangerous when wet), Class 5.1 (oxidisers), Class 5.2 (organic peroxides), Class 7 (radioactives)
- Compatibility split within Class 8 itself: acids and bases must be segregated from each other within the class. Concentrated sulphuric acid stowed adjacent to concentrated caustic creates a violent reaction risk if both leak.
For mixed-cargo ISO-tank containers carrying both acids and bases, the carrier requires separate stowage positions. For drum cargo of one Class 8 substance, segregation is usually carrier-managed.
Documentation chain and the China-side environmental layer
Standard DG documentation. Two extras for Class 8 from China:
- Production-side environmental compliance. Caustic soda and chlor-alkali production is environmentally regulated in China, facilities must hold a discharge permit and meet provincial MEE standards. A factory under environmental restriction can have its export ability suspended at short notice. Check that a new caustic supplier has a current environmental compliance certificate before signing a long-term contract.
- VAT export rebate sensitivity. Caustic soda VAT export rebate has historically been adjusted by the Chinese SAT, sometimes mid-quarter. A rebate cut from 13% to 9% raises the effective FOB price by approximately 4%. Build VAT-rebate sensitivity into long-dated supply contracts.
Operator note: HCl concentration creep on contract
Hydrochloric acid contracts written for “31% HCl FOB Tianjin” routinely deliver at 30.0 to 30.5%. The Chinese contract standard for industrial HCl is 31% nominal, but the production tolerance allows down to 29%. If your downstream process is HCl-titration sensitive, write the lower tolerance into the PO (“Reject below 30.5%”) and require pre-shipment third-party titration. Otherwise the cargo is “in spec” by Chinese standard but out of spec by your process need.
ISO tank builds for Class 8
For the bulk-liquid Class 8 cargo lane the right ISO tank build depends on cargo concentration and metallurgy. Concentrated 98% sulphuric acid and oleum ride T14 stainless (no bottom outlet, frangible disc plus tell-tale gauge). The China-Australia HCl 35% / NaOH 50% / sodium hypochlorite lane runs in T11 PE-lined carbon-steel-with-LDPE-liner builds. T14 PTFE-lined covers 70% HF and aggressive halogenated chemistry where PE fails. Class 8 PG I corrosives mandate T8 or stronger with no bottom outlet. The full T-code matrix at /iso-tanks cross-references every Class 8 cargo type.
Related terms
IMDG umbrella code. UN number. Packing group. ISO tank for bulk corrosives. Marine pollutant, many Class 8 substances are also marine pollutants. Segregation table for stow compatibility.