The EPA rule is designed to assist facilities and communities in efforts to lessen the number and
severity of serious chemical accidents. Under EPA's RMP, facilities must complete a hazard
assessment to evaluate potential effects of an accidental release of any regulated substance
present at or above the threshold quantity. The hazard assessment also must evaluate the impact
of significant accidental releases on the public health and environment. OSHA's PSM Rule
requires only a qualitative evaluation of a range of possible safety and health effects on
employees in the work place resulting from a release.
The hazard assessment of a regulated substance requires evaluation of a range of accidental
release scenarios, including:
"Worst-case" accidental releases
Other more probable releases
Potential offsite consequences
Five-year accident history for the facility
The EPA rule defines "worst-case" release as the instantaneous loss of all of the regulated
substance in a process, with failure of all passive and active mitigation systems. Once the
worst-case and other significant accidental scenarios are identified, facilities would be required
to analyze the potential offsite consequences associated with these scenarios using source release
and air dispersion modeling. This analysis would include fires, explosions, and hazard material
Air dispersion modeling would be used to evaluate the fate and transport of the regulated
substance for the offsite consequence analyses. At a minimum, the offsite analyses would
estimate the possible rate of release, the quantity released, the duration of the release, and the
distances in any direction that the substance could travel before it dispersed enough to no longer
pose a hazard to the public health or the environment.
Along with calculating the severity of the consequences, source term modeling would be used to
calculate release rate as a function of time and other release characteristics.
Under the EPA rule, facilities would be required to update the offsite consequence analyses of
their risk management plans no longer than every five years. Updates would be required sooner,
if changes at the facility or its surroundings might change the results of the risk management
plan to any significant degree.
A final element of the hazard assessment is compiling and documenting a five-year history of
releases of the regulated substances. EPA's RMP would require the facility to document the
releases that caused, or had the potential to cause, offsite consequences. The accident history
The substance and quantity released