Hazard Assessment cont'd

DOE-HDBK-1101-2004

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

releases.

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

must include:

The substance and quantity released

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