Re: Need Help with Radon

["Leo M. Lowe - SENES Consultants Limited" <llowe@senes.on.ca>]

Hello:



I am on Digest mode on Radsafe so I apologize if the message below has 

already been discussed.



The following was asked:



	"Appendix B, table 1 to 10CFR20 lists the ALI for Rn-222 as 1E+02 uCi or 4

	working level months.

	1) Is it still true that limits regarding the inhalation radon progeny are a

	primary guide based on intake, as opposed to a derived from a dose based

	limit?

	2) If so, how is radon dose reported on a Form 5 equivalent? Is it assumed

	that an ALI of 4 WLM, corresponds to 5 rem CEDE? How is compliance with

	limits demonstrated when there are intakes from multiple isotopes?"



Limits for the inhalation of radon progeny are based on exposure and are 

usually derived from epidemiologically-based risk factors, rather than 

dosimetric modelling.   For example, the ICRP equates, on a risk basis, 1 

WLM (working level month) of occupational exposure to 5 mSv , and therefore 

recommends an annual exposure limit of 4 WLM, corresponding to the ICRP 

recommended dose limit of 20 mSv/y (2 rem/y).  The conversion is 4 mSv/WLM 

for members of the public (averaged over all ages) because the risk per mSv 

is higher for members of the public.



I have not recently checked into the basis for the 10CFR20 ALI's; 

however,  the above-stated ALI  of 100 uCi of Rn- 222 corresponds to a DAC 

(derived air concentration based  on  a 2400 m3/y occupational inhalation 

rate) of 41.7 pCi/L, and a radon progeny exposure rate (at 100% 

equilibrium) of 5 WLM/y (actually 4.9 WLM/y for 2000 h/y), not 4 WLM/y.



Based on the ICRP conversion factor, the 5 WLM/y then corresponds to an 

annual dose of 25 mSv, or 2.5 rem.



Leo M. Lowe, Ph.D.

Principal, Senior Health and

Environmental Physicist



SENES Consultants Limited

121 Granton Drive, Unit 12

Richmond Hill, Ontario

Canada L4B 3N4

Tel:	(905) 764-9380

Fax:	(905) 764-9386

e-mail:	llowe@senes.on.ca

WWW:	www.senes.on.ca



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