Material Filter Testing
We got a Fluke 985 Particle Counter, which is a re-branded version of the MetOne HHPC+ Handheld Air particle counter used by hospitals and clean rooms to evaluate air quality. It is a 6-channel filter that simultaneously measures particle concentration of 0.3um, 0.5um, 1um, 2um, 5um, and 10um particles. It can be used to estimate the filter performance of different materials used as PPE, as well as verify if the labeling on PPE is accurate (or not).
I wanted to test the quality of PPE that was being sold by suppliers on Alibaba to verify their performance. Unfortunately, the sample that arrived so far performed far below the claimed KN95 rating.
Thanks to Jason Tongbai who started a similar effort a couple weeks prior. Here are his results
DISCLAIMER: We are not testing professionals. The method we use does not match any NIOSH, CDC, FDA, or certified procedure. This is not medical advice. These are estimates of performance using the equipment we have access to. We are sharing the results of tests we did with the samples we had. The true protective effectiveness of materials against infection is not something we can measure or claim. Additionally, a poor mask fit to a person's face/nose allowing air to pass around the material will significantly degrade effectiveness of even a good filter.
- We are not testing professionals. None of the methods or tools used here are certified by NIOSH, CDC, FDA, or any other authoritative agency. This is simply sharing the data we have collected with the tools, methods, and samples that we have at hand.
- Each sample was gathered using 2 cycles of 2L measurements. The meter reports Count/L for each of the 6 sizes.
- The meter was last calibrated on 2016-06-24. And the zero count filter was checked at the beginning of each session. We don't have the ability to re-calibrate the meter ourselves.
- An ambient air measurement with no filter was taken before and after each material sample. The average of the before and after samples are used as the baseline to compare the filter measurement. The ambient air quality fluctuated during the process, and this was used to help normalize the readings.
- The inlet of the meter was covered with the material sample, and secured with several turns of a rubber band holding each sample tightly around the lip of the inlet adapter.
N95 respirators provide the lowest level of acceptable protection against COVID-19. Therefore, OSHA now recommends that employers supply healthcare personnel who provide direct care to patients with known or suspected coronavirus with other respirators that provide higher protection than N95s. This includes N99 or N100 filtering facepieces, reusable elastomeric respirators with appropriate filters or cartridges, or powered air purifying respirators (PAPR).
- According to this source, it seems we care the most to filter out the 1-10 micro meter sized particles which the top 3 mask filters do well.
- Every paper towel brand will surely perform differently. Unfortunately we no longer have the packaging of this particular paper towel.
- This source (suayla.com) mentions specific shop towel brands that can provide 87% particle filtration.
For complete details and the raw data, here is the interactive data set.
Breathability through these fabric. Measure pressure drop across fabric for which this doc may have hints to give us ideas on how to measure that.