| Summary: | 碩士 === 中山醫學大學 === 職業安全衛生學系碩士班 === 103 === The recent studies have shown high concentration of bacterial that sampled from the HVAC (heating, ventilating, and air conditioning) system was observed in the hospital, included clinics, wards, emergency department, and dentistry clinics. Obviously, the HVAC systems in above cases were poorly sterilized and had bred microorganisms in the ducts. However, an ideal HVAC system not only can provide comfortable environment for medical employees, but also should reduce the concentrations of bioaerosols. As it is hard to evacuate the whole hospital patients and then sterilize the ventilation ducts, a real-time sterilization unit that located in the ventilation ducts is a critical method to control the bioaerosol-transmitted infections in hospitals.
The objective of this research was to develop a real-time sterilization unit and evaluate the unit under wind tunnel system. The real-time sterilization unit consists of porous filter media and UVGI (ultraviolet germicidal irradiation) modules. A Collison nebulizer was used to generate Bacillus subtilis spores and Escherichia coli as challenge aerosols. A radioactive source, Am-241, was used to neutralize the challenge particles to the Boltzmann charge equilibrium. Andersen 6-stage samplers were used to sample bacteria concentration upstream and downstream of the new real-time sterilization unit. The results showed the new real-time sterilization unit could be used to reduce the bacteria concentration; however, the unit still needs to be studied under field conditions.
The research installed real-time sterilization units in the ducts of the HVAC system. Two hospital wards and one nurse station located in central Taiwan were recruited in the experiment. Andersen 1-stage, 6-stage samplers, AGI-30, Biosampler and aerodynamic particle sizer were used to measure bacteria and fungi concentration from supplying air before and after installing the real-time sterilization units. The test conditions included different face velocities, and measured the duct condition: relative humidity and temperature. The attenuation rate of ultra violet germicidal irradiation (UVGI) and ageing effect of Nickel-filter-based real-time sterilization unit had also be taken into account.
The result showed that the non-coating Nickel-filter-based real-time sterilization unit revealed large size aerosol bounce during air duct velocity between 2.4 to3.5 m/s. This phenomenon decreased the collection efficiency when aerosol larger than 4.7 μm (based on the cutoff size of six-stage Andersen impactor). However, the non-coating Nickel-filter-based real-time sterilization unit revealed small size aerosol penetrating through it during air duct velocity between 1.4 to1.9 m/s. The fact decreased the collection efficiency when aerosol smaller than 1.7 μm, and this could be concluded as failure of mechanical filtration force for the period of low sampling velocity. Therefore, the possible collection and disinfection range of the non-coating Nickel-filter-based real-time sterilization unit was about 1.7 to 4.7 μm. The average bacteria disinfection rate of two wards and nurse station of six-stage Andersen impactor, single-stage Andersen impactor, and AGI-30, was 67.7 %, 40.8 % and 99.3%, respectively. The attenuation rate of four-9W-UVGI after 90-hour-irradiation was between 91 to 96 %. Moreover, the tensile strength of Nickel-filter was decreased to 78 % after 123-hour-UVGI-irradiation. The results recommended that the Nickel-filter-based real-time sterilization unit should coat with silicone oil to avoid the large aerosol bounce effect, and was better to use the unit in main ducts under high face velocity. Furthermore, in order to avoid the attenuation of UVGI, to save the energy, and to maintain the tensile strength of Nickel-filter, the UVGI of the Nickel-filter-based real-time sterilization unit was suggested not lighting on all the time.
|
|---|
