[Code of Federal Regulations]
[Title 40, Volume 15]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR68.28]

[Page 165-166]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 68_CHEMICAL ACCIDENT PREVENTION PROVISIONS--Table of Contents
 
                       Subpart B_Hazard Assessment
 
Sec. 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 Sec. 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 Sec. 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

[[Page 166]]

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 Sec. 68.42; and
    (2) Failure scenarios identified under Sec. 68.50 or Sec. 68.67.