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Frequent Advisor
Posts: 81
Registered: ‎04-05-2010

Pressure Differentials - How Many is Enough?

We moved into a new cleanroom suite last December.  A little on the small side but we are getting used to it.  You just don't put as much "stuff" in it (which is not really bad).  The door from the pharmacy opens into the anteroom.  As you enter the anteroom the door to the hazardous compounding room is to your left, non-hazardous to your right.  The anteroom is ISO Class 7 as required in this setup.  Three magnehelic gauges were installed.  One over each door.  Pressure differentials measured are anteroom/main pharmacy, anteroom/hazardous compounding room, and anteroom/non-hazardous compounding room.  These differentials are recorded daily. 


A few months ago we had a visit from the Texas Department of State Health Services.  They cited us for failing to comply with the following State Hospital Regulation:


" When IV solutions are prepared, the required laminar-flow system shall include a nonhygroscopic filter rated at 99.97% (HEPA).  A pressure gauge shall be installed for detection of filter leaks or defects."  (italics and underlining by me)


We were told that the 3 magnehelic gauges we had were not enough, in that they only measured pressure differentials between rooms and we needed to also be measuring the pressure differential from one side of the HEPA to the other (room pressure vs pressure in the ducts).  This is the only way to know if our HEPA filters leak or are defective. 


There are 5 HEPA filters in the ceilings of the 3 rooms and these required the installation of 5 more magnehelic gauges.  We now have a total of 8 magnehelic gauges in 3 small rooms that total about 360 sq. ft.  It seems to be a bit of overkill but the state said to do it so we did. 


The problem now is that we don't really know how to interpret the readings on the new magnehelics.  What should the pressure differentials be?  I assume they would be different for each room, maybe for each HEPA.  I can find no helpful information on this.  Can anyone help?


I also have a second question.  When our cleanroom suite was constructed the negative pressure hazardous compounding room was built without any return air registers.  ALL of the return air in that room is exhausted from the room through the CACI in the room.  Is this correct?  What if the CACI is turned off for repair or servicing?  Then the room will become positive, will it not?  And any contamination in the room could then be carried out of the room when the door is opened.  Any comments on this?


Please, anyone with any comments please jump in.




Robert Martin, PharmD