Threshold Planning Quantity (TPQ), explained

Published by Vertexium Environmental Solutions LLC · Last updated October 9, 2026

A Threshold Planning Quantity (TPQ) is the amount of an Extremely Hazardous Substance (EHS) listed in 40 CFR part 355 that triggers emergency planning duties. If an EHS is on site at or above its TPQ, you must notify your SERC and LEPC under EPCRA section 302. For Tier II, the EHS threshold is 500 lb or the TPQ, whichever is lower.

Where TPQs come from

EPA lists about 350 EHSs, each with a TPQ, in appendices A and B of 40 CFR part 355. TPQs range from 1 lb to 10,000 lb, depending on how toxic and how likely to become airborne the chemical is. EPA's Consolidated List of Lists is the easiest way to look one up; it also shows each chemical's Reportable Quantity and whether it is a TRI chemical.

Two duties a TPQ triggers

1. Emergency planning notification (EPCRA 302)

If any EHS is present at or above its TPQ, the facility must notify its SERC and LEPC and name a facility emergency coordinator who takes part in local emergency planning (40 CFR part 355, subpart B). Tier II asks you to say whether you are subject to section 302 (40 CFR 370.42(k)).

2. The Tier II threshold for that EHS

For Tier II, an EHS is reportable at 500 lb or its TPQ, whichever is lower (40 CFR 370.10(a)(1)):

TPQs from 40 CFR part 355, appendix A. Confirm current values in the eCFR or the List of Lists before relying on them.

Solids with two TPQs

Some solid EHSs carry two TPQ values, such as 500/10,000 lb. Part 355 says the lower value applies when the solid is a powder with particles under 100 microns, is handled in solution or molten form, or meets certain reactivity criteria. Otherwise the higher value applies (40 CFR part 355). This matters for some pesticides and industrial solids.

Mixtures

To check an EHS threshold, add the EHS in every mixture to any pure product on site. Multiply each mixture's weight by the EHS weight percent. Under part 370, components at 1% or less (0.1% for carcinogens) can be ignored (40 CFR 370.14). Part 355 has its own mixture rule for section 302 planning, so check both when an EHS is near its TPQ.

TPQ vs Reportable Quantity (RQ)

They answer different questions. The TPQ is about how much you store, and drives planning and inventory reporting. The RQ is about how much you release: a release of an EHS or CERCLA hazardous substance at or above its RQ within 24 hours must be reported immediately to the authorities under EPCRA section 304 and CERCLA section 103 (40 CFR part 355, subpart C). The List of Lists shows both numbers side by side.

Sources

1. 40 CFR part 355, emergency planning and notification (eCFR)
2. 40 CFR part 370 (eCFR)
3. EPA, Consolidated List of Lists

Related guides

• Tier II reporting thresholds, with worked examples
• EPCRA reporting requirements: sections 302, 304, 311, 312 and 313
• Tier II reporting: what it is, who files, and when