Understanding EHSs with Multiple TPQs


Some Extremely Hazardous Substances (EHSs) have more than one Threshold Planning Quantity (TPQ), which can be confusing at first glance. In this article, we'll explore why some EHSs have dual TPQs and what it means for facilities handling these substances.

What are EHSs and TPQs?

EHSs are substances that pose significant risks to public health and the environment due to their toxic, reactive, or otherwise hazardous nature. TPQs represent the minimum quantity of an EHS that facilities must report to local and state authorities under the Emergency Planning and Community Right-to-Know Act (EPCRA).

Why Do Some EHSs Have Dual TPQs?

Certain EHSs can exist in different forms or states, each with its own set of risks. For example, some substances may be non-reactive in specific forms or conditions, meaning they are less likely to cause a hazardous reaction. By having dual TPQs, authorities can account for variations in the risks associated with different forms of a substance, ensuring that the appropriate emergency planning and risk management measures are in place for each scenario.

Example: Sulfur and Its Dual TPQs

Sulfur is an EHS with dual TPQs. It has a lower TPQ of 500 pounds for its molten form and a higher TPQ of 10,000 pounds for its solid form. The lower TPQ represents a higher risk scenario, while the higher TPQ reflects a lower risk scenario. By having two separate TPQs, emergency planners can better account for the different hazards associated with the various forms of sulfur and prepare accordingly.

Types of Non-Reactive EHSs

Non-reactive EHSs can include substances in molten form, in solution, or with a particle size less than 100 microns. Each of these forms presents unique challenges and risks that must be taken into consideration when managing and reporting these substances.

For example, molten sulfur is less reactive and less likely to create a hazardous situation compared to solid sulfur. However, the molten form of sulfur still presents its own risks, such as potential burns or fires if not handled correctly. This is why it is crucial to have a separate, lower TPQ for molten sulfur, as it allows emergency planners to account for these specific risks.