Two threshold planning quantities (TPQs)
Several substances on the list of extremely hazardous substances (EHSs) have two threshold planning quantities (TPQs) listed in 40 CFR Part 355, Appendix A. When would a facility use the higher TPQ?
EHSs that are in solid form are subject to one of two different TPQs. A facility should use the lower TPQ if the solid is in powdered form and has a particle size less than 100 microns; is in solution; is in molten form; or meets the criteria for a National Fire Protection Association rating of 2, 3 or 4 for reactivity (§355.15(a)). If the solid does not meet one of these criteria, then the TPQ is 10,000 pounds (§355.15(b)).
A facility would only apply the 10,000 pound TPQ for an EHS when complying with the EPCRA Section 302 emergency planning notification requirements. For the purposes of EPCRA Section 311 or 312 reporting requirements (for example, Tier II reporting), a facility would use the threshold of 500 pounds or the designated TPQ in Part 355, Appendix A, whichever one is lower (§370.10(a)(1)).