Both anhydrous hydrogen chloride gas and its aqueous solution (hydrochloric acid) fall under subheading 280610. The physical form does not split the classification at the HS6 level, though US tariff-line schedules may distinguish them at the 10-digit level. Confirm the exact HTS10 code based on concentration and physical state.

Chlorosulfuric acid is a highly corrosive hazardous material subject to DOT hazmat transport regulations, requiring a proper shipping name, UN number, and emergency response information. Importers must also comply with EPA Toxic Substances Control Act (TSCA) import certification requirements. Consult a licensed customs broker for entry documentation specifics.