Theoretical d50 Calculation Results
Type of Inlet:
Flow Rate: LPM
Warning: In regulated clean areas, Low Flow recommended for use only in Grade A (ISO 5/6) clean areas due to reduced inlet count and required Feller Correction adjustments!
Number of inlets (holes or slits) in the sample head:
Warning: Very low inlet count!! Feller Correction will have divide by zero error when CFU enumeration exceeds hole or slit count. Feller Correction intended for multi-jet impactors only, not single stage slit-to-agar, impingment samplers, etc. [Macher, 1989]. Recommend not using this sample head in regulated applications.
Equivalent hydraulic diameter of the inlets: mm
Inlet Velocity: 0 (m/s)
ALERT: Inlet velocity is 0 (m/s), and unfavorably falls below 15 m/s. Low impaction velocity. MCPs (microbe carrying particles) will have a tendency to remain entrained in the airstream or not properly embed into the agar, thus, resulting in poor Physical Collection Efficiency [Ref. Stewart, 1995 and Whyte, 2014]. Recommend not using this sample head in regulated applications.
d50 = 0 µm
Definition of Results & Standards
ISO 14698-1:2003 (A.3.4.2) "Impaction velocity of the air hitting the culture medium is a compromise between (1) being high enough to allow the entrapment of viable particles down to approximately 1 µm; and (2) being low enough to ensure the viability of viable particles by avoiding mechanical damage or the break-up of clumps of bacteria or micromycetes." This has been broadly interpreted by the pharmaceutical industry that the d50 should be around 1 µm.
BS EN 17141:2020 (E.5.2) "The average equivalent diameters of microbe-carrying-particles (MCPs) that form the cfu are generally larger than 1 µm and a d50 value smaller than 2 µm is considered appropriate." BS EN 17141 section E.6 requires both an experimental d50 and a biological collection efficiency study be conducted to validate the above Theoretical d50.