How to maintain air pressure difference between clean rooms and passages and air locks?
Here is the systematic approach for maintaining the air pressure difference between clean rooms and air locks and passages before that lets understand that, the main function of a clean room is to prevent cross contamination, therefore clean rooms are supplied with air filtered through a series of filters and finally through HEPA filter which has a porosity of 0.3 micron to 0.2 micron, and they can filter out almost 99.997 % of the particles suspended in air. After air is filtered through HEPA filter air, it can’t cross contaminate the clean room, unless it travels from a place of high risk to lower risk, from the most contaminated place to the point of filling.
For example, from the personnel airlock to the point of filling inside the filling area inside the clean room. Personnel airlock is considered generating the highest level of particles due to man movement at a particular point.
The air from personnel airlock should not enter the inner side core area, in case of injection and sterile dosage form. And the Outer passage is less clean than the personnel air lock.
Therefore, as a strategy a pressure differential of 15 to 20 PSI is maintained between the outer passage and core filling area inner clean room, here in this case the inner filling area has more positive pressure than the air lock.
This can be reversed in case of tablet dosage form, where the risk of cross contamination is there from the inner clean room if it goes out, therefore the inner clean room in tablet dosage form is kept at lower pressure than the personnel air lock.
A pressure differential of 5 to 10 psi is maintained between the inner filling area and the personnel air lock.
How to increase pressure in the clean room?
Following are the steps to be taken both at the designing of the clean room and before the validation of the clean room.
During designing a cleanroom:
Increasing the number of supply points in the room results in an increase of air pressure in the clean room.
Increasing the CFM of the AHU will result in the total pressure increase in the air supplied by the AHU.
During operation or before validation:
Opening the supply grill out completely will result in increase in the air supplied by the AHU and air pressure.
Opening and closing the main outlet supply damper will result in increase or decrease of air pressure in the clean room respectively.
Opening or closing the supply port control liver in the clean room will increase or decrease air pressure in the clean room respectively.
By adapting the above control strategy, one can maintain the required pressure differential between the clean room, air lock and outer passage. After a settings are done on the AHU dampers, they are required to mark as 1, 2,3 etc and mark the favourable level and document the setting marking to maintain the differential between clean room and air locks and passage.