A facility has hydrofluoric acid which is a mixture of hydrogen fluoride and water.  The MSDS specifies that the mixture is 50% hydrogen fluoride and 50% water.  For purposes of reporting under Sections 311/312, should the facility report on the hydrofluoric acid mixture or the 50% hydrogen fluoride?

Since the MSDS for hydrofluoric acid specifies that it is a mixture of 50% hydrogen fluoride and 50% water, the facility would only have to report the 50% hydrogen fluoride if it exceeded the 100 pound threshold planning quantity.  See 40 CFR 370.14 (55 FR 30632, 30646 (July 26, 1990)).  Hydrogen fluoride is listed as the Extremely Hazardous Substance (40 CFR Part 355, Appendix A), and its Sections 311/312 reporting threshold is 100 pounds.  This is the case even though the CAS# for both hydrogen fluoride and hydrofluoric acid are the same.  If more than 100 pounds of hydrogen fluoride is present at the facility, the facility may report hydrogen fluoride by itself (i.e., 100 pounds of hydrogen fluoride) or by the total weight of the mixture (i.e., 200 pounds of hydrofluoric acid).