Checking HEPA filters?

Joe Harrington joeharr at
Sun Nov 3 20:30:29 EST 1996

posted/mailedmicrobe at (Steve Carpenter - Cascade 
Research Assoc.) wrote:
>A dry-ice fogger to check for airflow distribution within any HEPA filter 
>1. Purchase a 2' length of 4" diameter plastic pipe.  I use ABS sewer
>   pipe.  Close off one end, being sure to use glue to make it watertight,
>   and thread the other end so that you can place a screw-on cap on it. 
>2. Fit the side of the pipe with a plastic or metal tapered pipe fitting
>   over which you can place a 1/2-5/8" diam, 2-3' length of flexible, clear 
>   tubing.
>3. When you are ready to test, open the cap and put about a half quart to
>   a quart of hot water.  Throw in a good chunk of dry ice.  Screw on the
>   cap.
>4. Presto! - out comes fog through the clear tubing in the side of the 
>   pipe.
>  You can the use the fog in the chamber to see if the air is blowing 
>properly.  If you can access the plenum area above the filter, you may be 
>able to see leaks through large holes, depending on conditions.
>I have use this apparatus to successfully test many HEPA units in cleanrooms.
>-Steve Carpenter, Ph.D.
> Cascade Research Associates
>  & Abbey Lane Laboratory
> microbe at

Thanks for the informative responses regarding checking the filters.

I picked up the unit today in Mass.  It was a bit BIGGER than I 
anticipated, the filtered area was 72" by 32", and the entire cabinet
was custom made. I did some preliminary tests and it looks in very 
good shape and I'll try out the other suggestions. 

It was QUITE a challenge moving and we had to disassemble it 
to get it down the basement step.  But all in all, quite a deal for $450.

Thanks again to all respondents.


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