Equilibrium Factors

DOE-STD-1121-98

Example 4.7 (continued)

Example of Performance Specifications for a Bioassay Laboratory

Quality Control Spikes: HPS N13.30-1996 requires that control sample results, as a minimum, have a

relative bias statistics within -0.25 to +0.50 and a relative precision statistic of less than or equal to

0.4. At the levels to be used in spikes, the bias and precision should normally be smaller than the

limits in HPS N13.30-1996. The radiobioassay laboratory shall verify that these limits are met.

Instruments used for air sampling should be continuous instruments that make either time-averaged

or real-time measurements. They should be placed so as to measure as nearly as is practicable the

concentrations to which workers are exposed. In areas with large gradients of concentration or

equilibrium (e.g., outdoors), individual personnel monitors should be used for each worker.

Several good references are available for radon and thoron measurements (NEA 1985; NCRP 1990;

Fortmann 1994). Sheets gives a recent review of indoor thoron with many references (Sheets 1993).

4.5.2 Equilibrium Factors

If radon measuring instruments are used, radon progeny concentration should be inferred by

application of an appropriate equilibrium factor. In general, equilibrium factors should be measured

under a representative set of circumstances and for a representative time frame.

If it is not practical to measure equilibrium factors, a default 222Rn equilibrium factor of 0.4 (ICRP

1993a; UNSCEAR 1993) may be used for indoor areas with normal ventilation rates and outdoor areas

with radon sources no closer than 400 m (.1/4 mile;Table III). Average indoor equilibrium factors

increase with increasing particle concentration in air, and decrease with increased air exchange rate

(James et al. 1988; James 1994; National Research Council 1991; NEA 1985; UNSCEAR 1993). For

outdoor areas with local sources of radon and highly ventilated indoor areas, the appropriate equilibrium

factor should be determined by concurrent radon and radon progeny measurements made over a set of

conditions that present the range of equilibrium factors to be encountered when workers are present.

These measurements and the rationale for their application to inferring radon progeny concentration

should be documented in the internal dosimetry technical basis documentation.

Table III. Acceptable Default Equilibrium Factors for Radon (FRn)

Location/ Environment

Default Equilibrium Factor (FRn)

Indoors, normal ventilation

0.4

Indoors, unusual ventilation

Measure

Outdoors - no local radon sources

0.4

Outdoors with "local" radon sources

Measure