MadSci Network: Engineering

Re: How does diffusion factor in chemical concentrations above a vessel?

Date: Tue Apr 13 15:11:41 1999
Posted By: Bernadette Baca, Health Physicist, Uranium Licensing Project, Texas Dept of Health-Bureau of Radiation Control
Area of science: Engineering
ID: 923511308.Eg

This question will take some time in answering and the best possible way 
for me to relate the information to you and make sure the equations are 
correct, is to refer you to a few books I have used.

My background is in radiation safety so most of my primary texts with 
difussion of gases, vapors, and particulates are radiation based:

Radiological Assessment - Sources and Exposures; Richard E Faw and J. 
Kenneth Shultis; PTR Prentice-Hall, Inc. 1993 [mostly atmoshperic 
dispersion and diffusion, easy to read and apply to other fields]

Air Sampling in the Workplace - NUREG 1400; Nuclear Regulatory Commission 
(NRC)[this text, I think, may be located through the NRC website :  or]  It's been a LONG time 
since I used this text, but know that I used some time ago to figure out 
worker exposures before.

Within are several Regulatory Guides 
I have used as well.  I can't remember all the Guide numbers, but the 
titles of each should be a fair description of the Guide(s) and maybe one 
of these may be of help to you.

CRC Handbook of Chemistry and Physics; current edition should have some 
section on the various diffusion coefficients of a variety of substances 
and how to apply them?

I have a Fundamentals of Industrial Ventilation text somewhere at home.  I 
think there may be a section in it that might be of help to you.  Try a 
library search and I'm sure you'll find one - there are many editions from 
my recollection but all contain easy to understand info.

There is a professor at Texas A&M University I once took a class from and 
he was quite knowledgable in the Industrial Hygiene area.  His name is Dr. 
Rock.  The main Nuclear Dept. number is (409) 845-4161.  He's been a great 
help to me and may be as well to you.

I wish there was a simple and easy answer I could give to you, but in all 
accuracy, all I can do is provide texts with which might be of help to you. 
 Diffusion is not an easy component to undertake when trying to factor it 
in employee exposures.  There are a great many factors and variables to 
consider in developing an equation and such to define the diffusion of a 
chemical exposure.  I have taken several courses and each had a slightly 
different method for figuring out potential concentrations and exposures.

I'd also like to suggest searching the web a little more.  Try searching 
the governmental labs specifically for the information you are looking for 
- Lawerence Livermore; Los Almos National Lab; etc.  A lot of times there 
are articles and guides published with this information contained within.  
Also try DOE and OSHA sites.  Often thses sites will offer additional 
information to help you out.  

From my personal experience, I use the most conservative numbers possible 
in determining employee exposures; which would be direct readings of 
highest concentration.  The diffusion of the chemical would then be my 
safety margin to assure that overexposures (when having to actually work 
with the substances) would not exceed Regulatory Exposure Limits.

Hope this will help in some way.  If there may be of any additional help I 
may provide, contact me and I'll see what I can do to help.

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