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Accidental Releases: Analyzing Worst Case Scenarios

  • For Program I processes, one worst case analysis is needed for each Program I process.
  • For Program II and III process:
    • One worst case analysis must be conducted for toxic substances and one worst case analysis must be conducted for flammable substances.
    • Additional worst case analysis must be conducted if another covered process potentially affects other receptors.
  • Only administrative controls and passive mitigation is allowed.

    A)  Worst Case Release Quantity

    • For substances in a vessel, the greatest amount held in a single vessel, taking into consideration administrative controls.
    • For substances in a pipe, the greatest amount in a pipe, taking into consideration administrative controls.

    B)  Worst Case Release Scenario - Toxic Gases

    • If the toxic is normally handled as a gas or as an liquid under pressure, assume the release is over a 10 minute period.
    • If the toxic is normally handled as a refrigerated liquid, and the release is not contained by any passive mitigation, assume the substance is released as a gas over a 10 minute period.
    • If the toxic is normally handled as a refrigerated liquid, and the release is contained by passive mitigation, assume the liquid is spilled instantaneously to form a pool. The release rate must be calculated at the boiling point of the liquid.

    C)  Worst Case Release Scenario - Toxic Liquids

    • Assume liquid is spilled instantaneously to form a pool.
    • If no passive mitigation controls are in place, assume liquid spreads to a depth of 1cm. From this you should be able to determine the surface area and the release rate.
    • If passive mitigation is in place, use the surface area of the contained liquid to find the release rate.
    • If the release is not onto a smooth or paved surface, you can take into account the surface characteristics.
    • The release rate must account for the highest daily maximum temperature over the past three years, the temperature of the substance, and if its a mixture, the concentration of the toxic substance.

    D)  Worst Case Release Scenario - Flammables

    • Assume the entire substance vaporizes (explodes) in a vapor cloud explosion.