|MadSci Network: Engineering|
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 : http://www.nrc.gov/NRC/reference.html or http://www.sph.umich.edu/group/eih/UMSCHPS/law.htm] 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 http://www.nrc.gov/NRC/RG/online.html 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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