# Differential Pressure

Differential pressure plays an important role in pharmaceutical industries to protect & maintain the status of cleanrooms.

• What is the Differential Pressure?
• Importance Of Differential pressure.
• How is the differential pressure measured?
• Â WHO Standard For Differential Pressure?
• Types of Pressure?
• Precautions For Differential Pressure?

## What is the Differential pressure

The difference of atmospheric pressure between one area to an adjacent area is known as differential pressure.

Â In simple words, the difference of the pressure between the manufacturing area and the adjacent area, which may be the corridor or airlock, is known as differential pressure.

## Importance Of Differential Pressure

Differential pressure is a critical parameter in pharmaceutical industries which must be maintained and checked in cleanrooms as it has a great impact on contamination control.Â

• Differential pressure prevents contamination.
• Differential pressure helps to prevent cross contamination.
• Differential pressure helps to maintain the status of a cleanroom.
• Differential pressure is used to maintain the sterility of cleanrooms.

## How Differential Pressure Is Created?

Differential pressure in cleanrooms is created by using an HVAC system.

## Unit Of Differential PressureÂ

The SI unit of differential pressure is Pascal (Pa).

Differential pressure is also measured in inches of water column.

## How Differential Pressure Is Measured?

Two types of devices are used for measuring the differential pressure,one is known as magnehelic pressure measuring gauge and the second one is the manometer.

## Magnehelic Gauge

Magnehelic gauge is a round shaped pressure measuring gauge.It has a needle which moves to the right or left and indicates the value of pressure as positive or negative.

Magnehelic pressure measuring gauge measures the differential pressure in Pascal.

## Manometer

Manometer is generally an old fashioned device which consists of a curved glass rod partially filled with red color liquid.It also has a knob on it which is used to bring the level of red color liquid to the zero.

There are two openings at the top of the manometer labeled as high & low.

One narrow pipe comes from the inside area & is connected to these openings depending upon whether the inside area is kept at high pressure or low pressure.

Manometer measures differential pressure in inches of water column.

## WHO StandardÂ

Who guidelines for HVAC recommended differential pressure range is 10 to 15 Pascal.

### PrecautionsÂ

For differential pressure following are the critical precautions which must be followed.

#### No LeakageÂ

There should be no gaps in the ceiling,walls or windows of the area as leakage of air from these gaps will disturb differential pressure.

#### CalibrationÂ

Gauges used for measuring differential pressure must be calibrated.

#### Airlocks

An Airlock is established between the manufacturing area and the corridor to maintain the difference of the pressure if there is no clean corridor.

## Types Of Differential pressureÂ

Two types of pressure difference are created in the cleanroom.

• Negative Pressure
• Positive PressureÂ

### Negative Pressure

Negative pressure difference means the inside of the area is maintained at low pressure & adjacent areas like airlock or corridor have high or positive pressure.

Due to the above pressure difference the clean air moves from outside to inside.

Importance

The importance of negative differential pressure is as below,

• Prevent out flow of dust/powder from the processing area.
• Prevent chances of cross contamination.

Example

Negative differential pressure is maintained in the tablet granulation area where there is handling & generation of powder particles.

If the inside of the granulation area is kept at positive pressure as compared to adjacent areas, then this powder will move out & go in other areas resulting in cross contamination.

Only clean air moves inside due to negative differential pressure & there are no changes for powder to come out.

### Positive Pressure

Positive pressure difference means the inside of the area is at high pressure & adjacent areas like airlock or corridor have low or negative pressure.

Due to the above pressure difference the air moves inside of the area to the outside.

Importance

The importance of positive differential pressure is as below,

• Maintain sterility of cleanrooms.
• Prevent chances of contamination.

Example

In sterile processing areas the inside is maintained at high pressure as the main aim is to maintain the sterility of cleanrooms in sterile processing areas.

When the door of the sterile processing area is opened,the air moves from inside to outside & prevents the entry of microbes & contaminants to the area.

## Measurement Frequency

The differential pressure must be measured & recorded on regular intervals depending upon the organizational SOP & common practice is as follows

Measure differential pressure after 2 hrs in the areas where product is directly exposed e.g granulation area & after 4 hrs where product is not exposed directly i.e packaging hall.