Pressure differential is difference between atmospheric pressure between production area and its surroundings. It is measured in pascal using magnehelic pressure gauge.
According to WHO guidelines on HVAC system, 10-15 pascals of differential pressure is maintained between manufacturing and surrounding areas. Aseptic area should always be highly pressurized than the non aseptic area and air flow should be always from the aseptic to non aseptic area. This pressure differential is maintained by HVAC system. In tablet production area, pressure differential helps to prevent the cross contamination. Dust particles are generated in granulation and compression area; those can contaminate the other products being manufactured in adjacent areas. In sterile manufacturing pressure differential prevents entering the particles and microbes in sterile manufacturing rooms.
It is necessary to maintain the positive pressure in corridor than the tablet manufacturing areas to minimize the cross contamination. But positive airlocks should be there before entering the corridor while maintain the positive corridor than the manufacturing rooms. These airlocks prevent the direct air flow form uncontrolled area to controlled areas and helps to minimize the entrance of contaminated air into the controlled area. In sterile manufacturing area, manufacturing room is maintained in positive pressure than the surrounding corridor because there are more chances of microbial contamination instead of cross contamination.
It is important to carry out the pressure differential and recovery tests at the time of HVAC system validation. Pressure gauges should also be calibrated at the time of HVAC validation.
Related: HVAC system Validation Tests
It is important to have a good building construction and air tight windows and doors to maintain the required differential pressure. Pressure drop alarms are also used these days to indicate the low pressure in critical areas. Pressure differential may cause difficult to open the doors, particularly in the facilities having multi level differential pressure. Some facilities are using sliding doors to prevent this problem but it is difficult to make the sliding doors leak proof.
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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