How often to change "pre-filters" horizontal laminar air flow hood?

[arichards]

We have 2 USP797 compliant cleanrooms in our facility.  Each has a Baker Edgegard horizontal laminar air flow hood.  There is a prefilter composed of synthetic spongy material that prefilters the air prior to going through the HEPA filter.  We also have a Germfree horizontal airflow hood that uses disposable prefilters. For some reason, I thought that prefilters were to be changed monthly...however, we find that it simply is not dirty AT ALL and we are wasting time and money changing them out this often.  I could not find anything in the actual chapter 797 about frequency for changing pre-filters.   I would like to change our frequency for this to quarterly.  Is there a problem with doing that?

[cm]

You should contact Baker and ask what their recommendations are for their pre-filter changing.  However, to the best of my knowledge you do not need to change the pre-filter monthly unless your current P&P indicates that you must do it monthly.  Regardless, the pre-filter should be inspected monthly while cleaning the buffer room  to ensure that it is not clogged or dirty.   Otherwise, if the pre-filter is not dirty than I believe you can leave it in and continue to monitor it.  The first thing that I would do is review your current policy since this will tell you and anyone that comes in for an inspection how often you need to replace the pre-filter.  You can always change the P&P to change the pre-filter every 2 or 3 months, or quarterly.  Whatever you choose, your policy must state the same.