§ 68.28 Alternative release scenario analysis.

(a) The number of scenarios. The owner or operator shall identify and analyze at least one alternative release scenario for each regulated toxic substance held in a covered process(es) and at least one alternative release scenario to represent all flammable substances held in covered processes. (b) Scenarios to consider. (1) For each scenario required under paragraph (a) of this section, the owner or operator shall select a scenario: (i) That is more likely to occur than the worst-case release scenario under § 68.25; and (ii) That will reach an endpoint offsite, unless no such scenario exists. (2) Release scenarios considered should include, but are not limited to, the following, where applicable: (i) Transfer hose releases due to splits or sudden hose uncoupling; (ii) Process piping releases from failures at flanges, joints, welds, valves and valve seals, and drains or bleeds; (iii) Process vessel or pump releases due to cracks, seal failure, or drain, bleed, or plug failure; (iv) Vessel overfilling and spill, or overpressurization and venting through relief valves or rupture disks; and (v) Shipping container mishandling and breakage or puncturing leading to a spill. (c) Parameters to be applied. The owner or operator shall use the appropriate parameters defined in § 68.22 to determine distance to the endpoints. The owner or operator may use either the methodology provided in the RMP Offsite Consequence Analysis Guidance or any commercially or publicly available air dispersion modeling techniques, provided the techniques account for the specified modeling conditions and are recognized by industry as applicable as part of current practices. Proprietary models that account for the modeling conditions may be used provided the owner or operator allows the implementing agency access to the model and describes model features and differences from publicly available models to local emergency planners upon request. (d) Consideration of mitigation. Active and passive mitigation systems may be considered provided they are capable of withstanding the event that triggered the release and would still be functional. (e) Factors in selecting scenarios. The owner or operator shall consider the following in selecting alternative release scenarios: (1) The five-year accident history provided in § 68.42; and (2) Failure scenarios identified under § 68.50 or § 68.67.