Extremely Hazardous Substance

A substance on EPA's Section 302 list, subject to lower reporting thresholds and emergency planning notification.

An Extremely Hazardous Substance is one of roughly 350 chemicals EPA lists under EPCRA Section 302 as posing acute risk to human health in a release. Each carries a Threshold Planning Quantity.

Holding an EHS at or above its TPQ triggers emergency planning notification under Section 302. For Tier II purposes under Section 312, the reporting threshold is the lower of 500 pounds or the TPQ, rather than the usual 10,000 pounds.

Note the abbreviation collision: in this context EHS means Extremely Hazardous Substance, not environment, health and safety. Which is meant is usually clear from context, but not always.

Related terms

• Threshold Planning QuantityThe amount of an Extremely Hazardous Substance at which emergency planning obligations begin.
• EPCRA Section 302Requires a facility to notify state and local planners when it holds an Extremely Hazardous Substance at or above its Threshold Planning Quantity.
• Reporting thresholdThe quantity at which a chemical becomes reportable: 10,000 lb for most, lower for Extremely Hazardous Substances.
• List of ListsEPA's consolidated table of chemicals regulated under EPCRA and CERCLA, with their thresholds.

A plain-English explanation, not legal advice. Figures are the federal baseline; your state may differ, so see the state-by-state requirements.