developed from further analysis could prove to be misleading, since actions
might be taken to protect workers from hazardous material release when the true
risk is from the crash itself. For these reasons, this standard takes the position
that incremental risk to the offsite public is the appropriate metric for determining
whether the additional analysis of aircraft crash release scenarios is warranted.
It is recognized, however, that there may be unique cases for which
consideration of the impact of releases on onsite workers may be useful in the
absence of any impact on the offsite public. Specifically, one could envision a
situation where there is an unoccupied (or lightly occupied) facility containing
very large amounts of hazardous material in close proximity to a large
concentration of workers (but not close enough that these workers could be
directly impacted by the same crash that would cause the release) and where the
closest offsite member of the public is a great distance away. In such a case, it
is possible that the offsite exposure guideline would not be exceeded, but the
greatest risk to the workers would be from a hazardous material release.
To address such rare circumstances, three onsite exposure guidelines were
established. The basis for these guidelines is provided below.
Radiological exposure - the facility inventory exceeds 25 times the Hazard
Category 2 threshold quantities provided in DOE-STD-1027-92.
Basis: DOE-STD-1027-92 contains a table of radionuclides, showing the
maximum number of curies that could be released and cause a CEDE of
1 rem (0.01 Sv) at a distance of 300 m (984 ft) in atmospheric stability
Category D with a wind speed of 4.5 m/s (14.8 ft/sec). These curie
quantities are the thresholds for defining a facility as Hazard Category 2.
Clearly, 25 times these quantities would lead to a radiation dose of
25 rem (0.25 Sv) CEDE at 300 m (984 ft) and, as noted above, 25 rem
(0.25 Sv) CEDE is being taken as a surrogate threshold for 25 rem
(0.25 Sv) to the whole body, which is a threshold for early injury.