Every shipment of caustic soda carries several identifiers, and each one is used by a different party. Customs classify it by HS code, safety data sheets and registrations identify it by CAS and EC numbers, and carriers handle it by UN number, hazard class and packing group. When these match across the invoice, packing list, bill of lading and safety data sheet, clearance is routine; when they conflict, shipments get held. This page collects the identifiers in one place, with the reasoning behind each.
Quick reference: caustic soda identifiers
- Chemical name: sodium hydroxide (formula NaOH). Common names are caustic soda and, for solutions, lye or soda lye.
- CAS number: 1310-73-2.
- EC number: 215-185-5.
- CLP Annex VI index number: 011-002-00-6.
- HS code, solid (flakes, pearls, granules): 2815.11.
- HS code, aqueous solution: 2815.12.
- UN number, solid: UN1823, proper shipping name SODIUM HYDROXIDE, SOLID.
- UN number, solution: UN1824, proper shipping name SODIUM HYDROXIDE SOLUTION.
- Transport hazard class: 8 (corrosive).
- Packing group: II for the solid; II or III for solutions, as stated on the safety data sheet.
- GHS signal word and hazard statements: Danger; H314 (causes severe skin burns and eye damage) and H290 (may be corrosive to metals).
HS code 2815.11 vs 2815.12
HS heading 2815 covers sodium hydroxide, potassium hydroxide and the peroxides of sodium and potassium. Within it, subheading 2815.11 is sodium hydroxide in solid form and 2815.12 is sodium hydroxide in aqueous solution. Potassium hydroxide (caustic potash) sits at 2815.20.
The physical form of the solid does not change the code. Flakes, pearls, micropearls and granules all classify under 2815.11, and the grade, whether technical, food or rayon, does not change it either. What matters is whether the product is a solid or a solution.
The first six digits are harmonised internationally. National tariffs then add digits: eight for the EU Combined Nomenclature, ten for the UK commodity code and the US Harmonized Tariff Schedule. Duty rates, VAT, preferential rates and any trade-defence measures depend on the destination and the country of origin, so check the current destination tariff, for example the UK Integrated Online Tariff or the EU TARIC database, before you price a landed cost.
Two common errors cause avoidable queries. The first is declaring flakes or pearls under 2815.12 because the buyer plans to dissolve them; classification follows the goods as presented. The second is using the caustic soda code for formulated products, such as cleaning preparations that contain caustic soda, which may classify elsewhere. If you are unsure, ask your customs broker or apply for a binding ruling (an Advance Tariff Ruling in the UK, or Binding Tariff Information in the EU).
CAS 1310-73-2 and EC 215-185-5
The CAS number identifies the substance regardless of form or concentration. It appears in section 1 or section 3 of the safety data sheet and often on the certificate of analysis. Caustic soda solutions are mixtures of sodium hydroxide and water, and their safety data sheets list sodium hydroxide under the same CAS number.
The EC number is the identifier used under EU REACH and CLP, and is also used under UK REACH. If you import caustic soda into the EU or Great Britain, ask which company holds the registration that covers your import and whether your use is covered, and make sure the safety data sheet you receive reflects it.
UN1823 and UN1824: transport classification
Solid caustic soda travels as UN1823, SODIUM HYDROXIDE, SOLID, Class 8, packing group II. Solutions travel as UN1824, SODIUM HYDROXIDE SOLUTION, Class 8, with the packing group determined by concentration and stated on the safety data sheet. Sodium hydroxide is not classified as a marine pollutant for sea transport.
In practice this means:
- UN-approved packaging for the packing group, such as bags, big bags or drums bearing the UN specification mark
- Class 8 corrosive hazard labels and the UN number on every package, and placards on containers and tanks
- A dangerous goods declaration for sea freight and, for containerised cargo, a container packing certificate
- Segregation from acids during storage and transport
- Road transport under ADR within Europe and Great Britain, sea transport under the IMDG Code, and air transport under the IATA Dangerous Goods Regulations, which set quantity limits per package
Documents checklist for an import
- Commercial invoice showing the HS code, a precise description (for example, sodium hydroxide pearls, 99% minimum, technical grade), Incoterms and value
- Packing list with gross and net weights and the number of bags, big bags or pallets
- Bill of lading or sea waybill showing UN1823, Class 8 and packing group II
- Dangerous goods declaration and container packing certificate
- Certificate of analysis for the shipped batch
- Safety data sheet in English for the UK, or in the official language of the EU member state of import
- Certificate of origin where preferential duty or destination rules require one
- Any import permit that the destination country requires, which your customs broker can confirm
Keep the product description, HS code, UN number, packing group and weights identical across all documents. Most delays come from small inconsistencies, such as "caustic soda flakes" on the invoice and "sodium hydroxide, solid" with a different weight on the packing list.
Related products and further reading
Specifications and pack formats for the solid forms are on the caustic soda flakes and caustic soda pearls pages. For caustic potash, see potassium hydroxide, which is CAS 1310-58-3, HS 2815.20 and UN1813 as a solid. Our industrial manufacturing and formulation hub covers documentation and storage across other process chemicals, and the caustic soda buyer's guide covers grades, forms and specifications.
Frequently asked questions
Is the HS code different for caustic soda flakes and pearls?
No. Both are solid sodium hydroxide and classify under 2815.11. Only aqueous solutions move to 2815.12.
What is the UN number for caustic soda?
UN1823 for solid caustic soda and UN1824 for caustic soda solution. Both are Class 8 corrosives.
Is caustic soda a marine pollutant?
No, it is not classified as a marine pollutant. It is still a Class 8 dangerous good and must be declared, packed and labelled accordingly.
Does food-grade caustic soda have a different HS code?
No. The grade does not change the HS subheading, although national tariffs or import controls can treat end uses differently. Confirm with the destination tariff.
Can caustic soda be shipped by air?
Yes, as dangerous goods under the IATA regulations, within the quantity and packaging limits they set. Commercial quantities normally travel by sea and road.