01-06-2011 01:52 AM
USP 797 requires a positive differential of 0.02 to 0.05 in. w.c between the positive pressure compouding room and the anteroom. Would this differential be the same between the anteroom and the general pharmacy?
A negative differential of not less than 0.01 in. w.c is required between the negative pressure compounding room and the anteroom. Is there an upper limit to the negative differential or is anything above 0.01 in. w.c. allowed?
Robert Martin, PharmD
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01-11-2011 08:47 AM
The final language of this part of the chapter is not a clear as the members of the Sterile Compounding Committee had discussed. The idea is to maintain a cascading pressure differential so the air flows from the cleanest part of the facility (buffer area) through the ante area and out to the general pharmacy. If you have a pressure differential of positive 0.02" w.c. between the buffer and ante area and 0.02" w.c. between the ante and general pharmacy, then you have a robust pressure schematic (cumulative pressure differential between the buffer area and general pharmacy would be 0.04" w.c.
For hazardous drug compounding, the ISO Class 7 ante area will be your pressure sink, meaning that a minimum negative-pressure of 0.01" w.c. is required. There is no upper limit to this pressure but you don't want it TOO negative making opening the door difficult. Your certifier should be able to assist in setting up these pressures.
09-21-2012 02:22 PM
I have read several of your comments about pressure differentials from the buffer area to the ante room to the general pharmacy and you have eluded to the "cascading effect" several times. If that is the case, wouldn't the buffer area need to be higher than the ante room and it be higher than the general Pharmacy? From your example here and on another Forum question, you had drawn a diagram where the buffer area was 0.02 AND the anteroom was 0.02. Would the buffer area need to be higher than 0.02?
Confused in Paradise?!
David Watson R.Ph.
Central Georgia Home Infusion
Macon, Ga. 31211
09-21-2012 03:40 PM
I think you are measuring a change in pressure of 0.2. The 0.2 is the DIFFERENCE between the two areas being measured. So, they can have the same measurement but different air pressures in the rooms.
09-22-2012 09:13 AM
You are correct. The pressure diff from the buffer area to the general pharmacy area would be at least 0.04" to achieve the cascading pressures.
Buffer Area --> Ante Area = at least 0.02" w.c. positive pressure
Ante Area --> general pharmacy = at least 0.02" w.c. positive pressure
Buffer Area-->general pharmacy = 0.04" w.c. positive pressure.