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lorenbrichter
Fabric & filter efficacy testing
(Bringing over from email @Its-Gardner)
This particle approach seems doable, though the vacuum/pressure situation still needs to be designed.
Polystyrene microspheres in solution are readily available, and it appears that nebulizers can be used for dispersal. (I had asthma as a kid and may still have my old nebulizer at my parents house)
Nebulizer as delivery system of polystyrene microspheres https://www.tandfonline.com/doi/full/10.1080/03079450601028845
https://www.bangslabs.com/sites/default/files/imce/docs/TSD%20746%20web.pdf Challenge testing is another method used to determine pore size that can accommodate membrane materials with various pore sizes and shapes. It also allows for material properties of the membrane and target particulate to play a role in determining the membrane’s filtration efficiency. Challenge testing involves the administration of one or more challenge particle types to a membrane followed by the analysis of particle size and abundance both upstream and downstream of the filter.
Challenge testing of synthetic and biological membranes and filters is used for a variety of applications such as: • evaluating filtration efficiency of common commercially available filter classes (e.g. 0.2µm pore-size air filters, particle reduction filters, bioburden reduction filters, lab-grade and sterilizing-grade filters, etc.); • aerosol challenge to test HEPA and ULPA filter integrity and in situ monitoring of cleanroom installation; • evaluating integrity of synthetic barrier materials (e.g. latex gloves) to prevent viral-based disease transmission; • evaluating fouling and biofilm formation on synthetic membranes; and • evaluating media for filtration efficiency in removal of parasites or microorganisms from drinking water.
Filter challenge studies today often make use of highly uniform undyed, fluorescent, or visibly dyed polystyrene microspheres as surrogates for biologic or environmental particulates (e.g. microorganisms, pollens, dioctylpthalate esters (DOP), colloidal silica, A/C test dust, etc.) in order to reduce potential health risks and costs associated with the use of pathogens, atomized oils, etc.
Polystyrene is generally considered to be an inert polymer and it has a density of ~1.05 g/cm3 (i.e. slightly greater than that of water). Uniform polystyrene microspheres are available in a wide range of diameters (0.02µm – 10µm+) with a variety of surface modifications (e.g. nonfunctionalized, carboxyl-modified, amine-modified, etc.), and beads may be coated with protein or other molecules via straightforward methods to impart desired surface charge, hydrophilicity, or other properties. Visibly dyed and fluorescent versions of polystyrene microspheres feature encapsulated dyes, so the surface of dyed beads is also available for required modifications or coatings. A color palette of our visible dyes and excitation/emission spectra for our fluorescent dyes may be found in TechNote 103 under the Technical Support section of our website.
A variety of methods are employed for detecting polystyrene microspheres on filters, in the sample effluent, etc. Traditional methods for detecting undyed polystyrene microspheres include: microscopy (optical and electron), automated particle counters, turbidimetry and other light scattering-based techniques. Likewise, epifluorescence microscopy and fluorescence spectrophotometry have been widely used for detecting fluorescent polystyrene beads.
Current equipment:
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(2) PerfectPrime AQ9600, PM 0.3/2.5/10 Μm Air Quality Particle/Dust Detector/Counter https://www.amazon.com/gp/product/B071RF6B2Y/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
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Festool sander and vacuum (maybe for quick & dirty dust creation per http://www.fwwa.org.au/Art005_WoodDust_c1.pdf pg 7)
Apparatus rough layout: -dual particle counters -dual valves suggested by Bill -pre/post filter flow/pressure measurement -use of polystyrene microsphere particle solution -aerosolized particles with nebulization
Other filtration setups seen on web...
https://www.nbcnews.com/health/health-news/making-your-own-face-mask-some-fabrics-work-better-others-n1175966
https://www.businessinsider.com/homemade-mask-using-hydro-knit-shop-towel-filters-better-2020-4
https://nypost.com/2020/04/04/shop-towels-filter-better-than-t-shirts-for-diy-coronavirus-masks/
TESTING EQUIPMENT RENTALS www.eco-rentalsolutions.com
Fit Testers TSI 8030 Portacount Pro Respirator Fit Tester TSI 8038 Portacount Pro Respirator Fit Tester TSI 8040 Portacount Respirator Fit Tester TSI 8048 Portacount Respirator Fit Tester with N95
Particle Counters TSI 9306V2 Aerotrak Handheld Particle Counter - 0.3-1 micron range TSI 8525 P-Trak Ultrafine Particle Counter - 0.02-1 micron range
Particle Generator - NOT LISTED FOR RENT, but Suay Sew rented one (see photo) https://www.tsi.com/products/aerosol-generators-dispersers/polydisperse-generators/particle-generator-8026/
Cyclone and Dust Collection Research https://billpentz.com/woodworking/cyclone/cyclone_plan.cfm#air_volume "For fine wood dust such as created when using fine sandpaper, we only need about 50 FPM airspeed to overcome normal room air currents and move this dust. For typical sawdust we need to move the air at about 3800 FPM and for larger chips we need to move the air at about 4500 FPM. Ideally we should move right at 4500 FPM airspeed for picking up the normal range of wood chips. Many air engineers design instead at 4000 FPM because this airspeed is ample to pick up the material most fire marshals consider dangerous."
Power ratings of a mid range Festool dust extractor:
Simple Testing setup using single particle counter https://github.com/jcl5m1/ventilator/wiki/Material-Filter-Testing
https://smartairfilters.com/en/blog/ultimate-guide-homemade-face-masks-supplemental-data/
How the testing worked Smart Air aimed to mimic the test setup used by Cambridge University researchers, known as a Henderson apparatus, in which a fan blows air and particles through the mask material. The materials were tested for their ability to filter large-sized (1 micron, similar to the size of the Ebola virus) and small-sized (0.3 micron, the size of the smallpox virus) particles and for their breathability factor. For reference, COVID-19 coronavirus particles measure 0.06-0.14 microns in size, but 5-10 microns when in droplets.
First off, we used ambient air pollution for our tests. The air we breathe contains thousands of tiny particles, some of which are the same size as viruses. We did this so as not to have to work with any nasty viruses or bacteria. We lined two fans up in series to generate a strong airflow, enough to blow through each material at 0.3m/s. That’s similar to speed of the air when exhaling through your mouth.
At the end of our test tunnel, we placed a 10cm x 10cm specimen of each material on the end of the tube, and adjusted the fan to measure 0.3m/s on our anemometer. For some thick materials, our two-fan setup wasn’t powerful enough to reach this speed. Our results reflect which materials these were.
After setting up the material and the airflow, we then proceeded to use our Met One GT521 laser particle counter to measure the number of particles the materials could capture. Met One is the company that makes the big BAM monitors that most governments use to measure air pollution, so we’re in good hands here.
We tested the particle capture effectiveness of each material at capturing 1.0 micron and 0.3 micron particles. The 1.0 micron size mimics the Bacillus atrophaeus bacteria used by the Cambridge researchers (0.93-1.25 microns in size). It’s also a size that can be considered similar in range to coronavirus droplets (5-10µm). 0.3 micron particles are typically considered the most difficult to capture, and so was chosen here as a ‘worst case scenario’. It can give a reasonable estimate for effectiveness of each material at capturing 0.1 micron particles – the size of the coronavirus when not in droplet form.
For each material, downstream air was samples for 30s with and without the test specimen in place, and repeated 3 times. Averaging these values gave us our 0.3 and 1.0 micron capture effectiveness for each material.
Relative calibration of our particle counters. Used smoke from candle for particulate matter. Counter A averages ~22% higher reading than Counter B in the 0.3 micron range.
Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks - single layer and multi-layer hybrid testing
https://pubs.acs.org/doi/abs/10.1021/acsnano.0c03252?fbclid=IwAR0PqrJJ71EYncJZdlQRLMz0ULgU2mR0JwQIkJ8yUvoZlStVr4vQMERnTNQ#