Offsite Consequence Analysis

• 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.

• 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.

• 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.

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

• 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.

• 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.

• 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.

• 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.

• 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.

Documentation

• 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.