[Code of Federal Regulations]
[Title 40, Volume 15]
[Revised as of July 1, 2006]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR68.22]

[Page 162-163]
 
                   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.  68.22  Offsite consequence analysis parameters.

    (a) Endpoints. For analyses of offsite consequences, the following 
endpoints shall be used:
    (1) Toxics. The toxic endpoints provided in appendix A of this part.
    (2) Flammables. The endpoints for flammables vary according to the 
scenarios studied:
    (i) Explosion. An overpressure of 1 psi.
    (ii) Radiant heat/exposure time. A radiant heat of 5 kw/m\2\ for 40 
seconds.
    (iii) Lower flammability limit. A lower flammability limit as 
provided in NFPA documents or other generally recognized sources.
    (b) Wind speed/atmospheric stability class. For the worst-case 
release analysis, the owner or operator shall use a wind speed of 1.5 
meters per second and F atmospheric stability class. If the owner or 
operator can demonstrate that local meteorological data applicable to 
the stationary source show a higher minimum wind speed or less stable 
atmosphere at all times during the previous three years, these minimums 
may be used. For analysis of alternative scenarios, the owner or 
operator may use the typical meteorological conditions for the 
stationary source.
    (c) Ambient temperature/humidity. For worst-case release analysis of 
a

[[Page 163]]

regulated toxic substance, the owner or operator shall use the highest 
daily maximum temperature in the previous three years and average 
humidity for the site, based on temperature/humidity data gathered at 
the stationary source or at a local meteorological station; an owner or 
operator using the RMP Offsite Consequence Analysis Guidance may use 25 
[deg]C and 50 percent humidity as values for these variables. For 
analysis of alternative scenarios, the owner or operator may use typical 
temperature/humidity data gathered at the stationary source or at a 
local meteorological station.
    (d) Height of release. The worst-case release of a regulated toxic 
substance shall be analyzed assuming a ground level (0 feet) release. 
For an alternative scenario analysis of a regulated toxic substance, 
release height may be determined by the release scenario.
    (e) Surface roughness. The owner or operator shall use either urban 
or rural topography, as appropriate. Urban means that there are many 
obstacles in the immediate area; obstacles include buildings or trees. 
Rural means there are no buildings in the immediate area and the terrain 
is generally flat and unobstructed.
    (f) Dense or neutrally buoyant gases. The owner or operator shall 
ensure that tables or models used for dispersion analysis of regulated 
toxic substances appropriately account for gas density.
    (g) Temperature of released substance. For worst case, liquids other 
than gases liquified by refrigeration only shall be considered to be 
released at the highest daily maximum temperature, based on data for the 
previous three years appropriate for the stationary source, or at 
process temperature, whichever is higher. For alternative scenarios, 
substances may be considered to be released at a process or ambient 
temperature that is appropriate for the scenario.