Styrene polymerizes exothermically if not stabilized, so bulk shipments are transported with a polymerization inhibitor — typically 4-tert-butylcatechol (TBC) or similar — at specified concentration levels. Importers must verify that inhibitor concentration remains within the agreed specification upon arrival, as degradation during transit can create safety and quality issues. Certificates of analysis confirming inhibitor levels should be required from suppliers.

Importers must submit a TSCA certification (either positive or negative) with each entry. Because styrene is listed as a hazardous air pollutant and a substance under TSCA review, importers should also confirm whether any enhanced reporting obligations under EPA's Chemical Data Reporting rule apply to their import volumes and intended use.