Viral Filtration Efficiency Test – Increased Challenge
The Increased Viral Filtration Efficiency (VFE) test is normally performed on filtration materials and devices such as housed filters, pulmonary filters and cartridges. It is meant for materials and devices designed to provide protection against biological aerosols and which can withstand a more severe challenge.
This test is necessary for making marketing claims about the viral filtration efficiency of the filtration material. This procedure was modified from Nelson Laboratories’ standard VFE procedure in order to employ a more severe challenge than would be experienced in normal use. This method was adapted from ASTM F2101.
- ASTM F2101
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VFE125 - Virus Filtration Efficiency (VFE) at Increased Challenge
VFE125: Minimum 3 samples recommended; each samples must be 4 x 4 inches (10 x 10 cm) minimum or an entire housed filter
Study OutlineThe Increased Viral Filtration Efficiency (VFE) test offers a number of advantages over other filtration efficiency tests. It has been used with little or no modification for years and provides a standard reference for comparison of filtration materials. The Increased VFE procedure is very reproducible, easily performed and provides a more severe challenge to most filtration devices than would be expected in normal use.
The Increased VFE test determines the filtration efficiency by comparing the viral control counts to test article effluent counts. The test is conducted using the bacteriophage phiX174 as the challenge organism.
A liquid suspension of phiX174 is aerosolized using a nebulizer and delivered to the filtration media at a constant flow rate of 30 liters per minute (LPM). The aerosol droplets are collected in all-glass impingers (AGIs) in parallel. The challenge is delivered for a 1-minute interval and sampling through the AGIs is conducted for 2 minutes to clear the aerosol chamber. The titer of the assay fluid is determined using a standard plate count technique.
The number of viral aerosol droplets contacting the filter media is determined by conducting challenge controls without filter medium in the test system.
Challenge controls are maintained at 1 x 106 plaque forming units (PFU) with a mean particle size (MPS) of 3.0 ± 0.3 µm. This allows filtration efficiencies to be reported up to >99.9999%.
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