Bacterial Filtration Efficiency (BFE) of Medical Face mask Materials This instrument is designed as per the International Slandered specifications This instrument is used for evaluating of medical face mask materials for bacterial filtration efficiency. The medical face mask material which is to be tested is clamped between a six-stage cascade impacter where Petri disk kept with agar and an aerosol chamber. The bacterial aerosol is introduced into the aerosol chamber using a nebulizer and a culture suspension of staphylococcus aureus. The aerosol is drawn through the test material using a vacuum attached to the cascade impacter. This collects aerosol droplets which penetrate the test material. The agar plates are incubated for 48 hours