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  • Worst-case release scenarios with gases liquified by refrigeration

    When evaluating the worst-case release scenario for spills of liquid toxic substances, the owner or operator should assume that the maximum quantity within the vessel or pipe was released instantaneously to form a liquid pool (40 CFR §68.25(d)(1)). For regulated toxic substances that are normally gases at ambient temperature, the…

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  • Do environmental receptors include areas that are not Federal Class I areas?

    Do environmental receptors include areas that are not Federal Class I areas under the CAA? Yes. The list of environmental receptors in Part 68 includes areas in addition to those that qualify as Federal Class I areas under CAA section 162. Under Part 68, national parks, monuments, wilderness areas, and…

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  • Double wall tanks and "passive mitigation"

    Performance of the hazard assessment required under 40 CFR Part 68, Subpart B, includes analysis of both worst-case release scenarios (40 CFR §68.25) and alternative release scenarios (40 CFR §68.28). In each of these analyses, passive mitigation systems may be taken into consideration. If a tank has a "double wall,"…

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  • How must an owner estimate the population when defining off-site impacts?

    How must an owner or operator estimate the population when defining off-site impacts as part of the facility’s risk management plan (RMP)? The owner or operator must estimate the residential population within a circle with its center at the point of the release and a radius determined by the distance…

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  • Worst-case release scenarios for toxics and flammables involving the same process

    At my facility, if the worst-case release scenarios for regulated toxic substances and the worst-case scenario for regulated flammable substances involve the same process, must I analyze both? Yes. If the worst-case release scenarios for regulated toxic substances and regulated flammable substances in Program 2 and 3 processes are associated…

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  • Are roads considered public receptors?

    A process covered under 40 CFR Part 68 is eligible for Program 1 requirements if it meets all of the criteria listed at 40 CFR §68.10(b). One of those criteria is that the distance to a toxic or flammable endpoint for a worst-case release assessment is less than the distance…

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  • Does "consider off-site consequences" mean perform an environmental impact assessment?

    What does EPA mean by “consider offsite consequences”? Do we have to do an environmental impact assessment (EIA)? EPA does not expect you to do an EIA. Potential consequences to the public and the environment are already analyzed in the offsite consequence analysis. In the PHA, EPA only expects you…

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  • Are wetlands included in the definition of "environmental receptors"?

    No. EPA has defined environmental receptors as natural or state parks, forests, or monuments; officially designated wildlife sanctuaries, preserves, refuges, or areas; and Federal wilderness areas, that are easily identified on local U.S. Geological survey maps (40 CFR §68.3). Therefore, wetlands would not be reported in the hazard assessment under…

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  • Worst-case Scenario for Flammable Mixtures

    For the risk management program, where the concentration of the regulated flammable substance in the mixture is one percent or more by weight of the mixture, the entire weight of the mixture must be applied toward the 10,000 pound threshold quantity for the flammable substance unless the owner or operator…

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  • Do quantities in co-located vessels have to be aggregated for worst-case release scenarios?

    Pursuant to the risk management program (RMP) regulations, a facility owner or operator must conduct an off-site consequence analysis that includes modeling of a worst-case release. If a single process is comprised of several co-located vessels, must the total quantity in all the vessels be aggregated to determine the worst-case…

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  • For toxic endpoints, are milligrams per liter (mg / L) equivalent to parts per million (ppm)?

    The endpoint concentrations for regulated toxic substances under the risk management program rule (40 CFR Part 68 Appendix A) are listed in units of milligrams per liter (mg/L). Is this equivalent to parts per million (ppm)? No, mg/L is not always equivalent to ppm. Whereas ppm is a volume-to-volume or…

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  • What does "relief system design basis" mean?

    Relief systems include, but are not limited to, relief valves, relief headers, relief drums, and rupture disks. Design basis means documenting how the loads and sizes of the relief system, as well as inlet and outlet sizes, were determined. This includes a description of overpressure scenarios considered, the scenario that…

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