In the ASTM F2101 test method, the Bacterial Filtration Efficiency (BFE) of a mask is calculated by the following formula:
BFE (%) = (number of bacterial particles passing through the mask / number of bacterial particles in the initial spray) x 100
The steps are as follows:
1. Measure the number of bacterial particles passing through the mask: The recovered bacterial particles are counted, usually using biological culture methods or equipment such as particle counters to measure the number of bacterial particles passing through the sample.
1. Measure the number of bacterial particles in the initial spray: When conducting a spray test, the number of bacterial particles sprayed by the spray device is measured and recorded beforehand.
1. Calculate the bacterial filtration efficiency: Divide the number of bacterial particles transmitted through the mask by the number of bacterial particles in the initial spray and multiply by 100 to obtain the bacterial filtration efficiency of the mask (expressed as a percentage).
For example, if the number of bacterial particles in the initial spray is 1,000 and the number of bacterial particles passing through the mask is 10, then the bacterial filtration efficiency is (10/1000) x 100 = 1%.
With this calculation, the bacterial filtration efficiency of a mask can be evaluated, i.e. the ability of the mask material to filter bacterial particles. A higher bacterial filtration efficiency means that the mask is more capable of filtering bacteria.