Isokinetic Particle Sampling in Unidirectional Flow

To maintain compliance with regulations and produce products with limited risk, pharmaceutical companies manufacture products in controlled environments such as cleanrooms. Cleanrooms reduce the risk of variability and particle contamination and are defined as rooms in which air filtration, air distribution, utilities, materials of construction, and equipment are maintained in a controlled manner.

One common contamination management technique that cleanrooms employ is unidirectional airflow. A cleanroom with unidirectional airflow uses a controlled, steady velocity of air in parallel streamlines that move in one direction to minimize the potential movement of particle contamination. Unidirectional cleanrooms are typically designed using laminar airflow hoods that direct the air, and the airflow is designed to wash particles from a potential contamination source away from the process risk before being exhausted from the process area. The constant laminar flow of clean air ensures that this potential particle contamination does not extend beyond a field of control.

Unidirectional Airflow Design Requirements

Isokinetic particle sampling

There is an optimum air flow rate within unidirectional environments which is required for Isokinetic particle sampling to act as a sheathing air that washes particles from a potential contamination source away from the process risk before being exhausted from the process area. This ensures that this potential contamination does not extend beyond a field of control. This flowrate was historically defined as 90 feet per minute, which roughly converts to 0.45 m/s.

To effectively sample particles in this air without disrupting the airflow patterns (and therefore collect as accurately a reflection of the particles entrained within that air flow as possible), isokinetic particle sampling is required. The principles of isokinetic particle sampling are outlined in the paper.

 

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