Frequent Questions

Counting ammonia and ammonium hydroxide for TPQ and RQ calculations

Ammonia (CAS #7664-41-7) is listed on the Extremely Hazardous Substance (EHS) list found at 40 CFR Part 355 Appendix A and B, with a threshold planning quantity (TPQ) of 500 pounds.  A facility stores ammonium hydroxide (CAS #1336-21-6), which does not appear on the EHS list, on site in excess of 500 pounds.  Since ammonium hydroxide is essentially a mixture of ammonia and water, should the facility include the quantity of ammonia in ammonium hydroxide toward TPQ and reportable quantity (RQ) calculations for purposes of Sections 302 and 304 reporting?

The quantities of ammonia in ammonium hydroxide should be considered separately when determining reporting requirements under Sections 302 and 304.  This is consistent with the listing under CERCLA (40 CFR section 302.4), where ammonia and ammonium hydroxide are specifically and separately listed as hazardous substances.  Thus, ammonia (CAS #7664-41-7) and ammonium hydroxide (CAS #1336-21-6) are considered different chemicals.  The notification requirement in Section 302 applies to facilities with quantities of EHSs present on-site equal to or in excess of a TPQ.  Ammonia is considered an EHS, therefore, a facility with a TPQ or more of ammonia is required to provide Section 302 notification.  Since ammonium hydroxide is considered distinct from ammonia, and is not specifically listed as an EHS, it is not subject to emergency planning requirements.  A facility storing a large quantity of ammonium hydroxide, however, may have free ammonia in the headspace of a storage tank.  A facility must report the ammonia in the headspace of a storage tank under Section 302 if this amount of free ammonia equals or exceeds the TPQ at any time.  Section 304 applies to chemicals listed as either CERCLA hazardous substances (40 CFR 302.4) or EHSs.  Both ammonia and ammonium hydroxide are specifically listed as CERCLA hazardous substances and both chemicals, therefore, are subject to Section 304 reporting requirements.  Ammonia has a RQ of 100 pounds and ammonium hydroxide has an RQ of 1000 pounds.  If either chemical is released to the environment above its designated RQ within a 24-hour period, the facility is subject to Section 304 notification requirements (40 CFR 355.30).

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