Threshold Planning Quantity (TPQ)

Last Updated: July 22, 2020

Definition - What does Threshold Planning Quantity (TPQ) mean?

Threshold planning quantity (TPQ) is a parameter that limits the amount of hazardous substances at a particular location. It is defined as the maximum quantity of any hazardous substance stored or processed at a facility to minimize the risk should an accidental release occur. Threshold planning quantities are enforced by the US Environmental Protection Agency (EPA), and all facilities that handle hazardous chemicals are required to comply.

Corrosionpedia explains Threshold Planning Quantity (TPQ)

Industrial facilities must be aware of the types of hazardous chemicals that are onsite at any given time. Threshold planning quantities vary for different substances. Therefore, once the hazardous substances in an area are identified, companies can determine whether they exceed the stipulated threshold planning quantity for that particular material.

For example, gasoline and diesel fuel are both considered to be hazardous substances. For underground storage tanks, the threshold quantity for gasoline and diesel fuel is 75,000 and 100,000 gallons, respectively, according to the EPA.

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