Pharmacy Courses

Differential Pressure in Pharmaceutical Industry

The pressure differential is the difference between atmospheric pressure between the production area and its surroundings.

  • It is measured in Pascal using the magnehelic pressure gauge. 
  • This pressure differential is maintained by HVAC system.

According to WHO guidelines on HVAC system, 10-15 Pascal of differential pressure is maintained between manufacturing and surrounding areas.


  • To prevent any possibility of cross contamination.

Positive and Negative Pressure

In pharmaceutical cleanroom, positive and negative pressure are two important concepts to design and operation of cleanroom.

Where, positive pressure is used to maintain cleanliness and sterility in pharmaceutical cleanrooms and negative pressure is used to prevent the spread of hazardous substances.

In tablet production area, pressure differential helps to prevent the cross contamination. Dust particles are generated in granulation and compression area and those can contaminate the other products that 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 the corridor than the tablet manufacturing areas to minimize the cross contamination. But positive airlocks should be there before entering the corridor while maintaining the positive corridor than the manufacturing rooms.

The 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.

These airlocks prevent the direct airflow from uncontrolled area to controlled areas and help to minimize the entrance of contaminated air into the controlled area. In sterile manufacturing area, manufacturing room is maintained under positive pressure than the surrounding corridor.


1. It is important to carry out the pressure differential and recovery tests at the time of HVAC system validation.

2. Pressure gauges should also be calibrated at the time of HVAC validation

3. Pressure drop alarms are also can be used to indicate the low pressure in critical areas.

Some facilities are using sliding doors to prevent this problem but it is difficult to make the sliding doors leak proof.

Annex 1, specifically states that sliding doors are not permitted in sterile plants as they typically create uncleanable recesses, projecting ledges and recesses. For these reasons, they should not be used in non-sterile facilities either.

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Resource Person: Hassan Hussein

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