Microbial Removal Efficiency in situ Measurement of Exhaust Air HEPA Filters Employed in Cleanrooms

Airborne microorganisms can represent major health and economic risks to human and animal populations, thus they present a challenge to hospital operating theatres, food processing. For some cleanrooms containing pathogenic microorganisms, e.g. biosafety levels 3 and higher laboratories, infectious isolation wards, it is essential that the exhaust air has no infectious microbes to protect ambient environment. For this purpose, exhaust air HEPA filters should have good performance, and the in situ leak scan test should be conducted to validate the exhaust air HEPA filters and their surrounding support structures, such as gasket or seals, and the filter support structure, are free of leaks. Generally, these tests are performed with particulate matter, e.g. DEHS (di-ethyl-hexyl-sebacate), DOP(di-octyl-phthalate), PSL (Poly-Styrol Latex), instead of microorganisms. However, performance evaluation with microbes can directly reflect biocontamination control ability or microbial removal efficiency of exhaust air filters. This paper presents a detailed procedure for the microbial removal efficiency in situ measurement of exhaust air HEPA filters. This method is then challenged with four exhaust air HEPA filters used in a biosafety level 3 laboratory. The results show the removal efficiency of microorganisms is much larger than that of MPPS (most penetration particle size) particles and approximates 100%. It can be directly observed that the ambient environment near the laboratory can be effectively protected.