Procedure:


The masks were cut into pieces and tested in a circular acrylic air duct with an inner diameter of Indoor ambient aerosols or KCl aerosols were loaded as the pollutant source. The number concentrations of particles were measured by an optical particle counter (Aerotrak 9306, TSI Inc., USA). The concentrations were record every min for times upstream the respirator filter and then 2 times downstream. The single-pass filtration efficiency of particles with a certain size of was calculated by:


where and are the average particle number concentrations (pcs/L) at upstream and downstream of the filter, respectively.

The pressure drop across the respirator filter was measured by a differential gauge. The air temperature, relative humidity, and filtration velocity were measured by an airflow/temperature meter at the air duct exhaust.

Notes:

1. Sample size: cm diameter disk (active area = )
2. Ambient aerosol: simply use indoor air in the lab, temperature (not controlled), relative humidity
(not controlled), particle number concentration < pcs/L, typical aerosol size range:
3. KCl aerosol: using wt% KCl solution, pumping at 1 L/min. Temperature (not controlled), relative humidity
(not controlled), particle number concentration < pcs/L, typical aerosol size range:
4. Filter pre-conditioning: none
5. Flow rate: face velocity > (preferably > optional).
6. Number of tests: total (optional).
7. Filtration efficiency reported as a function of time (optional), filtration pressure reported as a function of time (optional), filtration efficiency reported as a function of particle size (optional).




How accurate? Comparison with NIOSH approved lab


Though this is not a sufficient test to establish conformity with NIOSH, EN149 or GB2626 standards, we have shown that results using this set-up conforms well to NIOSH pre-approval results (see in the Supplementary materials).
We have collected data on a set of N95 masks(n = 10) exposed to various sterilization procedures using the equipment described her and a test to NIOSH standards at a commercial laboratory(ICS Laboratories, USA) equipped to perform pre-certification testing. Mask instantaneous filtration efficiency values measured using the two tests had a correlation coefficient of 0.89 and all masks that passed our testing also passed ICS tests. Nonetheless, the data described here results should be interpreted as a relative, not absolute, measure of filtration efficiency.

All of the information below can be found in this paper.