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What sample air flow rate is best for my microbial sampler?

The regulations are not so prescriptive as to specify a particular minimum or maximum value for airflow rate through a microbial air sampler. This is true across the broad spectrum of regulations: EU GMP Annex 1: 2008, FDA Sterile GMP Guidelines, 2004, or ISO 14698-1 or -2.

The ISO 14698-1 document specifically requires all air samplers to be validated for both physical and biological collection efficiency because both recovery percentages are air flow rate and inlet geometry-dependent. Furthermore, ISO 14698-1 requires that the application be considered when choosing a sampler/flow rate. High flow rates may not be appropriate for aseptic batch monitoring because they sample too quickly to characterize the entire fill batch without risking drying out the culture medium, or they may risk damaging the viable particles of interest during the sampling process. Conversely, devices with very low flow rates may not be appropriate for sampling many locations in a large room because of the time that would be required to be allotted to the sampling.