Figure 4-1. PAS versus GAS versus CAM Example of the Degree of Correlation between Type of Sampling TMI-1983

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

by gross beta counting. A graph of the average air-activity concentrations determined by gross beta

counting by each of the three sampling methods is shown in Figure 4-1.

The five continuous air samples exhibited good internal agreement when averaged over either 12- or

24-hour periods. However, the grab samples averaged a factor of 3 higher than the continuous air-sampler

readings, and PAS samples were a factor of 34 higher. The major reason for this large difference was

attributed to resuspension of the surface contamination by the work in progress. These data, coming from a

thoroughly monitored and carefully analyzed air-sampling effort, are further evidence that GAS methods

should be viewed with caution.

Figure 4-1. PAS versus GAS versus CAM Example of the Degree of Correlation between Type of

Sampling TMI-1983

Even when the airborne-activity concentration in the breathing zone of a worker has been accurately

measured, there are other physical and physiological parameters that can produce significant uncertainties

in dose assessment. The established DACs are derived for each radionuclide assuming a standard volume of

air breathed in occupational situations, specified pathways to critical organs, the "standard man" metabolic

and elimination patterns, and the physical and biological properties of the isotope. Large variations are

encountered, however, in breathing rates and tidal volumes (whic h depend on working conditions), and

there are individual variations in such physiological parameters as lung clearance and metabolic rates. The

particle -size distribution of the aerosol and the actual solubility of the inhaled particles can significantly

affect the deposition and retention of airborne activity in the respiratory tract. The potential uncertainty in

the total dose assessment should include consideration of all of these factors, as discussed in the following

paragraphs.

Particle -Size Distribution

In the absence of actual measurement of particle -size distributions, an activity median aerodynamic

diameter (AMAD) of 1 um and a geometric standard deviation (GSD) of 2 is often assumed as a

4-6