Three Stage Filters

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Q: I have been told by a filter manufacturer that a three stage filtration system does NOT need to be used in accordance with Aerospace NESHAP.  Our facility is considered “New” as defined in the regulation, and we use inorganic HAPs in our spray booth.  Our vendor told us that provided our filter system passes the Method 319 test for a three-stage system we do not need to have three physical filters in place.  We would prefer to have only two stages in place, and our vendor has assured us that the filtration efficiency of our two-stage system meets the NESHAP requirements for three stages.  Do you agree with that information?

A:  The filter vendor is correct.  The Aerospace NESHAP allows you to use a single- or two-stage system provided that the filtration efficiency for the new booth is equivalent to that required by the NESHAP for a new booth.  For instance, as far as the EPA is concerned you can use a single HEPA filter if you wish, although it would not be cost effective to do so.

If your vendor can provide you with a letter certifying that the two stages he proposes to sell you will meet the requirements for three-stage filters, then you should be on safe ground.  I do suggest that you place the certificate on file, and also insure that the maintenance folks in the spray booth change the filters in accordance with the filter manufacturer's instructions.

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