Monday, 16 December 2019

Risk Considerations For The Use Of Unidirectional Airflow Devices In Microbiology Laboratories

Unidirectional airflow devices and microbiological safety cabinets are a common feature in many laboratories, including applications to achieve contamination control. Such devices are suitable for a variety of applications and especially where a demarcated clean air environment is required for processing smaller items and for practicing aseptic technique.

Unidirectional airflow, as defined by the World Health Organization, is a rectified airflow over the entire cross-sectional area of a clean zone with a steady velocity and approximately parallel streamlines. Conventional unidirectional airflow systems, where an ISO 14644 class 5/ WHO and EU GMP Grade A condition is required, have a guidance airflow velocity of 0.36 to 0.54 m/s. This form of airflow contrasts to turbulent flow, which is air distribution that is introduced into the controlled space and then mixes with room air by means of induction.

Such devices work by the use of in-flow unidirectional air drawn through one or more high efficiency particulate air (HEPA) filters, where air control designed to create a particle-free working environment and provide product protection (2). Air is taken through a filtration system and then exhausted across the work surface as part of the airflow process. Commonly, the filtration system comprises of a pre-filter and a HEPA filter. The device is enclosed on the sides and constant positive air pressure is maintained to prevent the intrusion of contaminated room air. Such devices are subject to physical problems and increased microbiological risks if they are not maintained correctly, especially in relation to air control.

In relation to this, Tim Sandle has written a new paper:

Sandle, T. (2019) Risk Considerations For The Use Of Unidirectional Airflow Devices In Microbiology Laboratories, Journal of Validation Technology, 25 (4): 1-10 at:

This paper assesses the most common risks affecting these laboratory devices. Prior to examining the devices and undertaking a model assessment, the paper discusses risk assessment in general, and looks at a generalized approach for conducting qualitative Failure Modes and Effects Analysis.

For further details, contact Tim Sandle

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology

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