-- Baseline measurements are used to establish a pre-exposure condition, either for
a new employee or as a result of a new work assignment. The standard,
Radiological Control, Ch. 1. (DOE, 2004), recommends baseline measurements
if workers are considered likely to receive intakes resulting in greater than 100-
mrem CEDE. It is a good practice to perform such measurements for newly hired
employees, intra-company transferees, or workers transferred from facilities
where bioassay measurements may not have been required. In addition, baseline
measurements can verify workers' status for special work assignments. For
plutonium bioassay, baseline measurements made before any occupational
exposure can be expected to yield no detectable results using current technology.
Exempting workers from baseline bioassay implies accepting any detectable
results as likely attributable to current occupational exposure. However, requiring
baseline measurements can potentially impact the schedule of short-term jobs;
the time required to obtain a chest count and a large-volume urine sample may
add a day or two delay to entry procedures. Moreover, missing a baseline for a
long-term employee who will be placed on a routine bioassay program is not
likely to be as troublesome as not obtaining a baseline for a short-term worker
who provides a termination sample that shows detection of plutonium after the
worker has left the site and is difficult to reach for follow-up.
-- Routine, or periodic, measurements are performed on a predetermined
schedule (e.g., an annual or quarterly frequency).
-- Special bioassay measurements are performed as follow-up to unusual
routine results or suspected intakes (See Section 5.9 for recommended
internal dosimetry indicator and action levels).
-- End of assignment or termination measurements are performed following
completion of specific work or at the time of termination of employment.
The standard, Radiological Control, Ch. 1. (DOE, 2004), recommends that
workers who participate in bioassay programs have appropriate termination
Bioassay classification is important because the purpose of a sample may affect
the collection and analysis or monitoring method chosen. For example, single-
void urine samples are not adequate for routine monitoring of potential
plutonium exposure, but can provide important information for dose-reduction
therapy following a suspected intake; samples representative of excretion over a
24-hour period should be collected for quantitative intake and dose assessment.
The date of sample collection (and possibly the time of collection) can be very
important to special monitoring performed to assess intake. However, these are
much less important with regard to periodic monitoring, for which measurements
are not expected to show detectable activity and when any detection whatsoever
is likely to initiate investigation and special bioassay.