Table VI. Three Options for Assigned Protection Factors for Rn, Tn, and Their Progeny

DOE-STD-1121-98

(41)

with the proviso that the APF cannot be less than 1.

Using the default values of 0.4 and 0.04 as examples, APFs can be no more than 40 for radon taken

together with its progeny, or 20 for thoron taken together with its progeny, regardless of the respirator's

performance for radon or thoron progeny.

The third option is to follow a recommendation by the National Institute of Occupational Safety and

Health (NIOSH). NIOSH has recommended that an APF of no more than 10 be allowed for respirator use

in underground mines due to the observation that workers do not use respirators more than 90% of the

time (NIOSH 1987). Similarly, the ICRP has recommended a protection factor of no more than 10 in

paragraphs 69 and 71 (ICRP 1986a), for practical reasons.

Table VI. Three Options for Assigned Protection Factors for Rn, Tn, and Their Progeny

Option

Radon

Radon Progeny

Thoron

Thoron Progeny

Measure Gas and Progeny

ANSI Z88.2-1992

1 # APF # 100 A FRn

1 # APF # 500 A FTn

Eq. Factor, Gas Measurement

NIOSH/ICRP

For airline supplied-air respirators, it is important to ensure that the intake air is filtered of radon

progeny and free of radon gas. Bottled-air respirators in which the air has been aged for 30 or more days

may be assumed to be free of radon and radon progeny.

7.5.8 Determination of Radon and Thoron Background

The background concentration used should be the best available estimate of the average

concentration that would have existed without the activity or source. For distributed sources of radon, it

is suggested that background be determined in accordance with DOE/EH-01737, Environmental

Regulatory Guide for Radiological Effluent Monitoring and Environmental Surveillance (DOE 1991).

One method of determining background is through measurements made before the commencement

of the activity or from measurements made in other unaffected parts of the same building (indoors) or

from measurements made at least 400 m (.1/4 mile) away from any known local source and/or up wind

(outdoors). A site-specific background should be used whenever possible. However, if determination of

the site-specific background is not feasible, a community-wide average may be used for up to one year

until local measurements have been made. If neither of these is practicable, then background values of

0.006 WL for radon progeny and 0.002 WL for thoron progeny may be used indoors and 0.002 WL for

radon progeny and 0.001 WL for thoron progeny may be used outdoors (see Table VII).