Extremely Hazardous Substances, or EHS, are treated differently from ordinary hazardous chemicals under EPCRA, with lower reporting thresholds and additional planning obligations. Here's how the list works and what it means for your facility.
Where the EHS list comes from
The EPA maintains and publishes the list of Extremely Hazardous Substances under EPCRA, along with each substance's threshold planning quantity (TPQ), the amount at or above which Section 302 emergency-planning requirements apply. This list is periodically updated, so a chemical's status, or its specific TPQ, isn't necessarily fixed indefinitely; it's worth checking the current list rather than relying on a figure from a previous reporting year.
The regulatory list is published in 40 CFR part 355, Appendices A and B. EPA's consolidated List of Lists brings EHS status, TPQ and CAS number together in one table, which makes it a practical starting point for an inventory-wide check.
How EHS thresholds differ from ordinary hazardous chemicals
Ordinary hazardous chemicals trigger Tier II reporting at 10,000 lbs. EHS substances trigger reporting at 500 lbs or their specific TPQ, whichever is lower, and many EHS chemicals have TPQs well below 500 lbs. This means a relatively small quantity of an EHS chemical can create a reporting obligation that a much larger quantity of an ordinary hazardous chemical would not.
Why EHS triggers Section 302 as well as Tier II
Having an EHS present at or above its TPQ doesn't just affect your annual Tier II report. It also triggers a Section 302 emergency planning notification to your SERC and LEPC within 60 days after your facility first becomes subject. Within that same 60 days, you must designate a facility emergency response coordinator and tell the LEPC who that is. After that, relevant changes go to the LEPC within 30 days. This is a one-time or as-needed notification, separate from your annual Tier II filing cycle, and it's easy to miss if attention is focused only on the yearly report.
Common EHS oversight risks
- Treating the flat 500 lb figure as a universal threshold, without checking whether a specific chemical's TPQ is lower
- Missing a Section 302 notification requirement because attention is focused on annual Tier II reporting instead
- Not re-checking the current EHS list when a new chemical is introduced to a process
- Assuming a chemical isn't EHS-listed based on outdated information, rather than the EPA's current published list
How to check whether a chemical you use is EHS-listed
The EPA publishes the current EHS list with associated TPQs directly. Cross-referencing every chemical in your inventory against this list, rather than relying on memory or a prior year's assumption, is the only reliable way to catch a newly relevant substance or a TPQ that's lower than the general 500 lb figure most people default to.
An annotated lookup, step by step
- Take the chemical identity from the current SDS: the component names and CAS numbers in Section 3 (composition), not just the trade name on the label.
- Search the official source by CAS number: EPA's List of Lists or 40 CFR part 355, Appendices A and B. Names vary between suppliers; the CAS number is the reliable match key.
- Confirm the chemical name on the list entry matches the SDS as a cross-check. A CAS match with a different name is a reason to stop and investigate.
- Read the EHS status and the TPQ from the entry, plus any note shown with it.
- Record the source, the version or date shown on it, the date you checked and who checked it, so the result can be re-verified next year.
| Field | Where to find it | What you record |
|---|---|---|
| Product and supplier | Inventory record; SDS Section 1 (identification) | Product name, supplier, SDS revision date |
| Component name and CAS number | SDS Section 3 (composition) | [Chemical name], [CAS number] |
| Concentration | SDS Section 3 | [Weight %, or the range as stated] |
| EHS status | List of Lists EHS column, or 40 CFR 355 Appendices A/B | Listed or not listed, matched by CAS |
| TPQ | Same list entry | [value from the list], in pounds |
| Notes on the entry | Any note or footnote shown with the list entry | Note text, or "none" |
| Source and version | Title and date or version shown on the source | [URL], [version or date] |
| Checked by and date | Your review | [Name], [date] |
Leave a field blank and flag it rather than filling it from memory or a prior year's record.
How Section 302 and Section 312 use the EHS information
Once a chemical is confirmed as an EHS, the same list entry feeds two separate checks with different numbers, deadlines and outputs.
Section 302 (emergency planning): compare the total amount of the EHS present at any one time with its TPQ. At or above the TPQ, notify the SERC and LEPC within 60 days of first becoming subject and designate a facility emergency response coordinator. This isn't repeated every year, but changes need to reach the LEPC within 30 days.
Section 312 (Tier II): compare the maximum amount present at any one time during the previous calendar year with 500 lbs or the TPQ, whichever is lower, and report annually by March 1. Because of the 500 lb cap, a chemical with a TPQ above 500 lbs can be reportable on the Tier II without triggering Section 302. For worked examples, see how to calculate reporting thresholds.
When an EHS is present as a component of a mixture, the Tier II total adds the component amount in every mixture (concentration × mixture weight) to all other quantities of that EHS on-site at the same time, under 40 CFR 370.14. Section 302 has its own provisions in 40 CFR part 355, so check them for mixtures rather than assuming the Tier II method applies.
Mixture data to collect for each EHS component
- Current SDS for the mixture, with its revision date
- EHS component identified by CAS number from SDS Section 3 and matched to the official list
- Concentration by weight recorded, noting which value you used if the SDS gives a range
- Mixture quantity converted to pounds, using the SDS density or specific gravity if stored by volume
- Component amount calculated as concentration × mixture weight
- Component amounts added across all mixtures and any pure product present at the same time
- Reporting option (component or whole mixture) recorded and kept consistent between Section 311 and Section 312 where possible
- Calculation reviewed, initialled and dated by a second person
Official source
The federal requirements described in this article are established under the Emergency Planning and Community Right-to-Know Act (EPCRA). Always verify current state-specific rules with your SERC.
The list itself is in the eCFR at 40 CFR part 355, and in EPA's List of Lists. Tier II mixture rules are in 40 CFR part 370.
Source40 CFR Appendix A to Part 355 – Extremely Hazardous Substances ListRegulatory statements in this article were checked against the official sources linked above on .