What was modified in the original Greene & Vesley Test method for BFE testing? Why is modified used?
Your question “What was modified in the original Greene & Veseley test method for BFE? Why is the modified used?” has left me a little perplexed.
When I was answering the query that I received on fluid resistant masks I based my answer on the newest ASTM (ASTM F2100 – 11 Standard Specification for Performance of Materials Used in Medical Face Masks) which was published in 2011. Although I mentioned the modified Green and Veseley test, I would have to say that since it was originally received for publication in 1961(making it a two years younger than myself) its methodology is a little antiquated compared to the newer ASTM testing. Also since it uses a human subject and counts all CFU’s that are expelled through a mask and deposited on an agar plates in an Anderson impactor, while said human is enunciating prescribed words , the Greene and Veseley test is far less controlled than the ASTM Testing , which uses a test microbe (Staph. Aurues) aerosoled to a prescribed size and pressure and counts the CFU’s that pass through the material being tested (this method also uses
the Anderson impactor for colletion of CFU’s).
As far as the difference between the original and modified Greene and Veseley tests, I am going to take an educated guess here (I have never claimed to be a scientist of any sort, I am first and foremost a Certified Sterile Processing Technician, with too many years for my own good of experience in the trenches) and that is that the modified test employs the use of a sampling chamber and Andersen impactor. To quote the original article from the Jounal of Bacteriology …..
“ Sampling Chamber. The sampling chamber was a plywood box (5′ x 16” x 16”) mounted vertically on an angle iron frame. A high efficiency (>99%) fiberglass filter formed the top surface of the box. A fixed metal port projected from the tapered bottom of the box and served as a connection to the air sampler. A sliding “guillotine-like” panel with a flexible plastic collar was provided to permit entry of the subject’s head and neck, at a point 4’ from the sampling port. A glass window was constructed on one side of the chamber for psychological comfort. The only air supply during a test was filtered through the fiberglass and the only source of contamination was the subject. When proper capping was observed and suitable entry precautions taken, a silent subject contributed less than one contaminant/ft³”
Again maybe I’m wrong, maybe there was another modification I seem to have missed. What I do know is that it is an old test with many controls missing. The newer ASTM testing methods with its controlled microbe, aerosol size, pressure differentials and challenge concentration seems much more reliable than someone saying sing and chew with a mask on in a wood box.