Research On Exhaust HEPA Filter In-situ Leak Test Methods Of Isolation Equipments Used In Biosafety Laboratory

In recent years, major outbreaks of epidemics and sudden public health hazards occurred frequently, emerging infectious diseases showed a trend of spreading worldwidely, and biological safety problems were widely concerned around the world. High-level biosafety laboratory played an essential role in the study of deadly infectious disease pathogens. High-level biosafety laboratory primary barrier isolation equipments, such as biological safety cabinets(BSC), negative pressure isolators(Isolator), individually ventilated cages(IVC) were usually the core operating areas to produce dangerous biological aerosol. Their exhaust HEPA filters as the key component of protective barriers should be detected to ensure no leakage. The current study on In-situ leak testing on HEPA filters of barrier isolation equipments was very little, so it was very necessary.In high-level biosafety Laboratories, most exhaust HEPA filters of the primary barrier facilities could not be accessible for scanning leak tests. The low-precision total penetration leak tests became the only choice for users. According to such situations and the applicable difficulties, this thesis studied on the application feasibility of sodium flame method, aerosol photometer method and particle counting method in leak tests. At present, the study of sodium flame method applied to In-situ leak test was very little, so the first part of this thesis studied on In-situ leak test application of sodium flame method, mainly focusing on sodium chloride aerosol generator suitable for In-situ leak test. Firstly, a series of experiments were taken to study the influences of primary factors on its generating aerosol to determine its structure and the operating parameters. In addition, the influences of the environment conditions on sodium chloride aerosol were also studied. Secondly, the testing principles of the three methods were different, so the second part made a comparative study on different detection methods to determine whether the test results consistent or not, then studied on the testing precision gap between total penetration leak test method and scanning leak test method. At last, the influences of leak testing conditions on total penetration leak test method were studied in the third part on the basis of the former two parts study.The research on aerosol generator showed that sodium chloride aerosol generator prototype with the laskin nozzle in condition that sodium chloride solution concentration was 4% and spray pressure was 100 KPa was able to be steady operation to produce aerosol particle mass median diameter(MMD) of 290 to 320 nm, count median diameter(CMD) of 48 to 55 nm with a geometric standard deviation(GSD) of 2.0 to 2.1; the aerosol mass concentration was around 0.6 mg/m3 and the photocurrent value was around 50000μA; in addition, there was no obvious moisture absorption phenomenon for sodium chloride aerosol when the environmental relative humidity increased to 70%. The comparative study of three detection methods showed that the testing results of three detection methods for the leak filter were approximately equal; the local penetration ratio relative deviation of three detection methods for the same leak point was of 1.3% to 13.3%, and the overall penetration ratio relative deviation was of 4.5% to 22.2%; Significant differences of test results were formed between total penetration leak test method and scanning leak test method. For the same leak point, the overall penetration ratio was only 2.4%~6.1% of the local penetration ratio. At last, the research on the influences of field testing conditions on total penetration leak test method showed that the running fan produced a large amount of dust to make particle counting method difficult to apply to In-situ leak test, which had no influence on sodium flame method or photometer method; the presence of the elbow or fan at the downstream of the filter made the overall penetration ratio drop to 0.9%~4.6% of the local penetration ratio.