Hydrofluoric acid is an acutely toxic hazardous material subject to DOT transport regulations, EPA Risk Management Program (RMP) thresholds at receiving facilities, and TSCA import certification. Importers should also verify whether the concentration level triggers additional state-level chemical reporting requirements at the destination.

Fumed silica and other forms of silicon dioxide that are chemically defined compounds generally fall under 281122. However, natural quartz or crystalline silica in mineral form is classified in the chapter covering mineral products. The key test is whether the product is a chemically defined compound or a naturally occurring mineral.