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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.

I saw your answer to the question about the proper gowns for PPE in decontamination and noticed that you mentioned fluid resistant masks as part of the PPE. Is there a recommended mask for this purpose?

The classification of masks and respirators is a complex subject with multiple classifications for a variety of working situations, so I am going to just focus on those that pertain to working in decontamination. Let me begin with the fact that you do not need a respirator for decontamination, although they would offer you great protection from aerosolized particulates, respirators must be fit tested and worn properly to be effective. Also the more filtration they provide the harder they become to breathe through. Respirators are best for use in patient rooms where respiratory isolation is indicated.

I did state that a mask for decontamination should be fluid resistant and when searching for masks you will see different resistance qualifications and wonder what they might refer to, so I will give some examples here to help out.

If you see   BFE > 99%   This qualification is based on testing done by the ASTM (ASTM F2101-01) for Bacterial Filtration Efficiency, the material being tested is mechanically subject to 3 micron droplets of liquid aerosol containing   Staphylococcus aureus at a flow rate of 28.3 L/min, and a material of this classification is capable of filtering out more that 99% of this aerosol. (Make sure this BFE rating is based on the ASTM F2101-01 testing and not on the older Modified Greene and Vesely Test, where a human subject says the word “Chew” and “Sing” distinctly at 10 second intervals for 1 minute through the material being tested in a closed container. The container is then cultured and a bacterial count is taken but there is no specific organism counted)

If you see   PFE>95%    This qualification is based on Submicron Particulate Filter efficiency testing done by the ASTM (ASTM F2299).This test uses 0.1micron latex spheres at a flow rate 0.5 to 25cm/s the particles are counted with a light scattering photometer before and after passing through the material being tested, so a PFE>95% would mean that more than 95% of these spheres were filtered by the test material.

NIOSH Particulate Filtration Efficiency testing for respirators, (yes I know I said you don’t need a respirator for decontamination) is a much more stringent.  For healthcare purposes N series respirators apply (N here = Not resistant to oil, the other two classifications are R- Resistant to oil and P-Oil Proof would include oil in their testing aerosol). The challenge here is ~0.3microns liquid sodium chloride aerosol at flow rate of 85L/minute. A collection of at least 95% of this by the material gives the respirator an N95 rating, at least 99% collection would be an N99 and anything 99.7% and over gives the material an N100 rating.(These N,R and P classifications truly only apply to respirators and not face masks)

If the masks make the claim ASTM F1862 120mmhg Fluid Resistance   This is the actual fluid resistance of the mask based on ASTM testing. In this challenge, a high velocity stream of synthetic blood is aimed at the material being tested at different pressures (80mmHg, 120mmHg and 160mmHg) to replicate blood exiting a puncture wound at a variety of blood pressures. An 80mmHg rating would be a Low fluid barrier classification, 120mmHg would be a Medium and 160mmHg a High.

Another thing you might see is a Differential Pressure Test (Delta P or ∆P) number   The lower the number here the more breathable the mask is but, the more breathable the mask is the less protection it offers.

Now if this is not complicated enough ASTM F2100-11 has prescribed new mask standards for fluid resistant face masks as follows.

ASTM Level 1

Low Fluid Resistance    80mmHg

Filtration Efficiency      BFE>95%

PFE>95% @ 0.1micron

Breathability-∆P            <4.0mm H2O/cm2

Flame Spread                  Class 1 (low flammability)

ASTM Level 2 

Moderate Fluid Resistance 120mmHg

Filtration Efficiency         BFE>98%

PFE>98% @ 0.1micron

Breathability-∆P             <5.0mm H2O/cm2

Flame Spread                   Class1 (low flammability)

ASTM Level 3

High Fluid Resistance       160mmHg

Filtration Efficiency          BFE>98%

PFE>98% @ 0.1 micron

Breathability-∆P               <5.0mm H2O/cm2

Flame Spread                    Class 1 (low flammability)


Wow that’s a lot of information right…. So now the choice is yours, but if it were up to me, knowing that surgical masks truly do not provided the optimum protection that a respirator does, I would at least choose one that provided me with the most, Like an ASTM level 3 Mask, or at least one that had all those qualities.