instantaneously onto the ground and either spread to a depth of
1 cm (0.4 in.) or cover a well-defined diked area if there is one.
The rate of evaporation will then be calculated using standard
formulas such as those provided by the Center for Chemical
Process Safety (CCPS) (Reference 6).
3. For refrigerated liquids, the material will likewise be assumed to
spill onto the ground and either spread to a depth of 1 cm (0.4 in.)
or cover a well-defined diked area. The rate of evaporation will
again be calculated using standard formulas such as those
provided by CCPS.
4. For a pipeline rupture, the complete contents of the pipeline up to
the nearest undamaged isolation valve(s) will be assumed to be
released as a puff.
5. For materials that can burn and form toxic products of
combustion, the burning will be assumed to be instantaneous,
with 100 percent efficient production of the toxic products.
In the above determinations, the respirable fraction will be assumed to be
100 percent. For releases that are potentially buoyant, the buoyancy will
be ignored for the purposes of the screening calculation.
Hazardous Material Offsite Exposure Determination. Reference 3
contains a series of nomographs for common hazardous chemicals that
provide dosage estimates under various conditions relevant to aircraft
crash scenarios. These nomographs serve to guide analysts and simplify
the screening process. They can be used to provide a screening value
for the site boundary Level of Concern for the materials and conditions
specified. If a particular facility has materials or conditions not covered by
the nomographs, an acceptable technique is given by the U.S.
Environmental Protection Agency's (EPA's) TSCREEN Code