RE: Radon and Respiratory protection

["Allen, David" <dka6@cdc.gov>]

I believe the reason the daughter products attach to dust in the air is

because they are electrostatically charged.  That same charge on a very

small particle is also a mechanism by which HEPA filters can remove the

daughters.  The HEPA filters should remove the unattached daughter products

by electrostatic attraction and the attached daughters by filtering the dust

particles to which they are attached.  In other words, the HEPA filtration

should be effective against radon daughters regardless.

 

Therefore, HEPA filtered respirators should be effective, but as the posts

below mention, if HEPA filtered ventilation is to be used, the potential of

increasing the unattached fraction should be considered.  In a typical

industrial work place, it would likely not be a problem, in a clean room

environment, it could be a problem.

 

As far as documentation, I believe Canberra worked on a CAM that would

remove radon daughters by this mechanism in order to help discriminate

between radon and long-lived alpha airborne.  The CAM worked well in a radon

chamber but not in a real life work environment.  I believe they wrote an

article in the Journal but I can't put my fingers on it right now.

 

        David Allen



-----Original Message-----

From: GELSG@AOL.COM [mailto:GELSG@AOL.COM] 

Sent: Thursday, September 04, 2003 6:59 PM

To: blc+@PITT.EDU; jbeckel@ameslab.gov

Cc: radsafe@list.vanderbilt.edu

Subject: Re: Radon and Respiratory protection





This has been a problem for me for over 15 years.  I believe Mr. Beckel has

touched on a valid point, one I discussed by email with Dr. Cohen a number

of years ago.



I do not disagree with the points that Dr. Cohen has made about reducing

dust particulates causing an increase in the unattached fraction of radon

daughters.  I think it is also important to restate the fact that filtration

will have no effect on the radon concentration.  But the largest contributer

to lung dose is from the daughter products attached to particulates which

deposit in the lungs and decay prior to biological removal.  Po-218 and

Po-214 in particular.



So far, I hope we are all in agreement.  I believe that, in the real world,

a HEPA filter will do a LOT of good in reducing the actual dose to people.

I'm talking about a place like my home where there are doors opening and

closing, windows that leak, people cooking, and grandchildren chasing the

cat.  The studies on unattached fraction were done in a laboratory where

scientists could control things like humidity and particulate

concentrations.  That was a necessity since particulate concentration was a

key parameter for measurement.  In that controlled, lab atmosphere, it is

easy to see how one could reach the conclusion that "reducing particle

concentration necessarily caused an increase in unattached fraction" of

radon daughters.



As long as there is no significant depletion in the number of particles in

the home due to the operation of a HEPA filtration unit, I think there would

be a large reduction in lung dose from radon (attached) daughters with very

little increase in the unattached fraction.  In other words, you would need

a particle source to replenish those carrying radon daughters that are

trapped on the HEPA filter.  If you don't have grandchildren chasing your

cat, light a couple of candles or run a humidifier in the winter and open a

window in the summer.  Frankly, I wonder whether any home would have a

significant increase in unattached fraction similar to that found in a

laboratory experimental chamber.



I think Dade Moeller suggested a similar radon dose reduction strategy quite

a few years ago, and the only argument I recall against such a strategy was

the fear of increasing the unattached fraction of radon daughters.  I don't

think that is a serious concern in the average home.  Are any of you aware

of any studies of unattached fraction in places other than an experimental

chamber?



G. L. Gels



In a message dated 9/3/03 12:26:22 PM Eastern Daylight Time, blc+@PITT.EDU

writes:









On Wed, 3 Sep 2003, Jay Beckel wrote:



> Do HEPA cartridges provide ANY protection at all in a radon atmosphere?

Are

> there any studies out there that would back up any theories of radon

> attachment to particles and therefore being caught up in the HEPA?



    --This is a complicated question. The danger from radon comes from

radon progeny which normally attach to fine dust particles. Thus, removing

dust from the air inhaled reduces inhalation of these, reducing the

"working level". But removing the dust from the air causes an increased

fraction of the progeny to remain unattached to dust particles, and

unattached radon progeny are more likely to attach to the bronchial

surfaces which makes them more dangerous. These two effects approximately

compensate, so little is gained by filtering dust out of the room air.

Filtering dust out of air as it is inhaled would be quite useful in

reducing exposure, but this is not convenient in most cases.

    There is no need for HEPA filters, which are to remove over 99% of

the dust. Removing 80% or 90% would do nearly as much good.