Exhibit 1
Required Parameters for Modeling (40 CFR 68.22)
WORST CASE ALTERNATIVE SCENARIO
Endpoints (§68.22(a))
Endpoints for toxic substances are specified in part 68 Appendix A. Endpoints for toxic substances are specified in part 68 Appendix A.
For flammable substances, endpoint is overpressure of 1 pound per square
inch (psi) for vapor cloud explosions.
For flammable substances, endpoint is:
Overpressure of 1 psi for vapor cloud explosions, or
Radiant heat level of 5 kilowatts per square meter (kW/m ) for 40
2
seconds for heat from fires (or equivalent dose), or
Lower flammability limit (LFL) as specified in NFPA documents or
other generally recognized sources.
Wind speed/stability (§68.22(b))
This guidance assumes 1.5 meters per second and F stability. For other
models, use wind speed of 1.5 meters per second and F stability class
unless you can demonstrate that local meteorological data applicable to
the site show a higher minimum wind speed or less stable atmosphere at
all times during the previous three years. If you can so demonstrate, these
minimums may be used for site-specific modeling.
This guidance assumes wind speed of 3 meters per second and D
stability. For other models, you must use typical meteorological
conditions for your site.
Ambient temperature/humidity (§68.22(c))
This guidance assumes 25 C (77 F) and 50 percent humidity. For other
models for toxic substances, you must use the highest daily maximum
temperature and average humidity for the site during the past three years.
This guidance assumes 25 C and 50 percent humidity. For other
models, you may use average temperature/humidity data gathered at the
site or at a local meteorological station.
Height of release (§68.22(d))
For toxic substances, you must assume a ground level release. This guidance assumes a ground-level release. For other models, release
height may be determined by the release scenario.
Surface roughness (§68.22(e))
Use urban (obstructed terrain) or rural (flat terrain) topography, as
appropriate.
Use urban (obstructed terrain) or rural (flat terrain) topography, as
appropriate.
Dense or neutrally buoyant gases (§68.22(f))
Tables or models used for dispersion of regulated toxic substances must
appropriately account for gas density. If you use this guidance, see Tables
1-4 for neutrally buoyant gases and Tables 5-8 for dense gases, or Tables
9-12 for specific chemicals.
Tables or models used for dispersion must appropriately account for gas
density. If you use this guidance, see Tables 14-1 7 for neutrally
buoyant gases and Tables 18-21 for dense gases, or Tables 22-25 for
specific chemicals.
Temperature of released substance (§68.22(g))
You must consider liquids (other than gases liquefied by refrigeration) to
be released at the highest daily maximum temperature, from data for the
previous three years, or at process temperature, whichever is higher.
Assume gases liquefied by refrigeration at atmospheric pressure to be
released at their boiling points. This guidance provides factors for
estimation of release rates at 25 C or the boiling point of the released
substance, and also provides temperature correction factors.
Substances may be considered to be released at a process or ambient
temperature that is appropriate for the scenario. This guidance
provides factors for estimation of release rates at 25 C or the boiling
point of the released substance, and also provides temperature
correction factors.
April 15, 1999
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