NAC459.95364. Parameters for analysis of off-site consequences.

     1. An owner or operator shall use the following endpoints when preparing an analysis of off-site consequences:

     (a) For toxic highly hazardous substances, the toxic endpoints provided pursuant to NAC 459.9533;

     (b) For flammable highly hazardous substances and explosives:

          (1) In a scenario that studies the potential effects of an explosion, an overpressure of 1 psi (0.0703 kilograms per square centimeter);

          (2) In a scenario that studies radiant heat and exposure time, a radiant heat of 5 kw/m² (1586 BTU per hour per square foot) for 40 seconds; or

          (3) In a scenario that studies the lower flammability limit, the lower flammability limit provided by the N.F.P.A. or other generally recognized sources; or

     (c) If an endpoint is not provided pursuant to NAC 459.9533 or a substance is not designated or classified as toxic, flammable or explosive pursuant to NAC 459.9533, the owner or operator shall define an appropriate endpoint that results in the greatest impact to employees and public receptors. The owner or operator shall define a toxic endpoint in a manner that is comparable to the health impacts defined by ERPG-2 of the Emergency Response Planning Guidelines Series, which is adopted by reference pursuant to NAC 459.95528, and shall define a flammable or explosive endpoint as set forth in paragraph (b).

     2. The owner or operator shall use a wind speed of 1.5 meters per second (4.9 feet per second) and an atmospheric stability class of F when preparing the worst-case release analysis, except that, if the owner or operator demonstrates that local meteorological data show a higher minimum wind speed or less stable atmosphere at all times during the previous 3 years, these minimums may be used. For an analysis of an alternative scenario, the owner or operator shall use the typical meteorological conditions.

     3. Except as otherwise provided in this subsection, the owner or operator shall use the highest daily maximum temperature during the previous 3 years and the average humidity for the site based on temperature and humidity data gathered on-site or at a local meteorological station for a worst-case release analysis involving a toxic highly hazardous substance. A facility using the R.M.P. Guidance for Off-Site Consequence Analysis, which is adopted by reference pursuant to NAC 459.95528, may use 25°C (77°F) and 50 percent humidity as values for these variables. For an analysis of an alternative scenario, the owner or operator may use typical temperature and humidity data gathered on-site or at a local meteorological station.

     4. The owner or operator shall analyze:

     (a) A worst-case release of a toxic highly hazardous substance assuming a ground level (0 feet) release.

     (b) An alternative scenario involving a toxic highly hazardous substance using the release height that is determined by the release scenario.

     5. The owner or operator shall use urban or rural topography for a worst-case release scenario or an alternative scenario, as appropriate. An urban topography has many obstacles, such as buildings and trees, in the immediate area. A rural topography has no buildings in the immediate area, and the terrain is generally flat and unobstructed.

     6. The owner or operator shall ensure that any table or model used for a dispersion analysis of a toxic highly hazardous substance appropriately accounts for gas density.

     7. For a worst-case release analysis, the owner or operator shall assume that a liquid other than a gas which is liquefied by refrigeration only is released at the highest daily maximum temperature based on data for the previous 3 years appropriate for the facility, or at process temperature, whichever is higher. For an alternative scenario, the owner or operator may assume that the substance is released at a process or ambient temperature which is appropriate for the scenario.

     8. As used in this section, “typical meteorological conditions” means the temperature, wind speed, cloud cover and atmospheric stability class that prevail at the site based on data gathered at or near the site or from a local meteorological station.

     (Added to NAC by Environmental Comm’n by R121-98, eff. 5-27-99; A by R137-04, 2-15-2005)