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Air Quality

Section 112(r) of the Clean Air Act - Accidental Release Prevention Program

On June 20, 1996, the U.S. Environmental Protection Agency (EPA) issued the Risk Management Program Rule under Section 112(r) of the Clean Air Act Amendment of 1990. This rule is aimed at preventing accidental releases and reducing the severity of those releases that do occur. This Rule has been amended and updated on several occasions.

The Risk Management Program has four major components:

Hazard Assessment

In the hazard assessment section of the Risk Management Program, facilities must evaluate the possible consequences of an accidental release to nearby communities, schools, hospitals, recreational facilities, and other public and environmentally sensitive areas by predicting the "worst-case" and "alternative" (i.e., more likely) release scenarios. These scenarios can be demonstrated using computer-based models. Facilities must also document past accidents that have occurred at the facility for the last five years.

Offsite Consequence Analysis

A)  Endpoints
  • Toxics: Use the toxic endpoints given in Appendix A of the Risk Management Program regulation.
  • Flammables: Flammables: For the worst case, use an overpressure of 1 psi explosion. For the alternative, use a radiant heat/exposure time of 5kw/m2 for 40 seconds.

B)  Wind Speed/Atmospheric Stability
  • Worst Case: For the worst case, use a wind speed of 1.5 m/s and F atmospheric stability class (nighttime weather conditions).
  • Alternative Case: For the alternative, use the typical meteorological conditions at the source.

C)  Ambient Temperature/Humidity
  • Worst Case: Either the highest maximum daily temperature in the previous three years and average humidity for the site or 25 C and 50% humidity.
  • Alternative Case: Typical temperature and humidity for your site.

D)  Release Height
  • Worst Case: Assume a release height of 0 ft.
  • Alternative Case: Release height will be typical of your process you are modeling.

E)  Temperature of Released Substance
  • Worst Case: Either the highest maximum daily temperature in the previous three years or the process temperature, whichever is higher.
  • Alternative Case: Release is at a process or ambient temperature appropriate for the process.

Worst-Case Release Scenario Analysis

  • 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.

Alternative Release Scenario Analysis

  • For each toxic substance, one alternative scenario must be submitted for each toxic substance. For example, if a facility has five (5) toxic substances, the Offsite Consequence Analysis must have one worst case analysis and five alternative scenarios.
  • For each flammable substance, one alternative scenario must be submitted to represent all flammables. For example, if a facility has six (6) flammable substances, the Offsite Consequence Analysis must have one worst case analysis and one alternative scenario for the worst case flammable substance.
  • For the alternative scenario(s), facility must create a scenario which is more applicable to the facility.
  • Consider a release scenario which is more representative of your facility, such as transfer hose releases, process piping releases, vessel or pump releases due to cracks, spills, and shipping mishaps. Consider five year accident history as a basis for the alternative scenario(s).
  • Active, passive, and administrative controls can be used for the alternative scenario(s).

Offsite Impacts

  • Within the impact radius circle, include:
    • Residential population numbers
    • Schools
    • Hospitals
    • Prisons
    • Recreational Areas
    • Major commercial, office, and industrial buildings
    • Parks (local, state, and national)
  • For population receptors, use most recent census data or other updated information.
  • For environmental receptors, use United States Geological Survey (USGS) data.

RMP - review and update information

  • Update the offsite consequence analysis every five (5) years
  • If changes in process, quantities, or any other aspect might either increase or decrease the impact radius for a particular regulated substance by a factor of two (2) or more, the facility must complete a revised analysis within six (6) months of the change and submit a revised RMP.
  • If a facility plans to use a regulated substance which was not previously included in the RMP, a revised offsite consequence analysis and RMP must be submitted before the new regulated substance is on property.


  • For worst case and alternative scenarios, the facility must have on site the description of the vessel/pipeline and substance selected as worst case, all assumptions and parameters used, and the rationale behind said assumptions. Documentation should include the anticipated effect the mitigation and controls have on the release rate.
  • Document the release quantity, release rate, and duration.
  • Methodology used to determine endpoints.
  • Data used to estimate population and environmental receptors affected.

Five Year Accident History

  • For each accidental release, document:
    • Date, time, and release duration.
    • Chemical(s) released.
    • Estimated quantity released in pounds.
    • Type of release and the source.
    • Weather conditions, if known.
    • On-site impacts.
    • Off-site impacts, if known.
    • Initiating event and contributing factors, if known.
    • Whether offsite responders were notified, if known.
    • Process or operational changes as a result of the release.

LandView VI: Electronic Environmental Analysis Tool - This website describes the LandView 6 software which contains a wealth of important environmental information that may be useful for facilities in identifying their site locations and potentially vulnerable populations.

Risk Management Program Guidance for Offsite Consequence Analysis (March 2009) - This is EPA's official RMP offsite consequence analysis guidance. This latest version represents the most up-to-date thinking on the subject, and has been technically reviewed by experts outside of EPA. Although it replaces the previous Offsite Consequence Analysis Guidance, if you have prepared your RMP using the previous guidance, you do not need to revise it based on this new guidance. This revision incorporates several new features, including chemical-specific modeling for ammonia, chlorine, and sulfur dioxide, temperature correction factors for calculations involving evaporating liquids, step-by-step procedures and worksheets to assist users, additional worked examples, and format changes.

It is also available broken down into Chapters and Appendices.

Risk Management Program - Related Links and Information

For more facility specific information see the Risk Management Programs Basic Awareness Brochures for Specific Sectors at EPA's Industry Guidance Website.

DHEC Accidental Release Prevention Contacts:

For more information please contact us at (803) 898-4123 or by email.