Research On Diffusion Pattern Of Microbial Aerosol And Airflow Organization Optimization In Hospital Wards

The transmission and deposition of pathogenic bioaerosols and the subsequent contamination of the air and surfaces is well recognized as a potential route of hospital cross-infection.The purpose of air filtration and purification in hospitals is to reduce the concentration of airborne pathogens to lower than the infectious dose.The use of mechanical ventilation systems in hospitals may be an effective intervention to block the transmission of aerosols.The mechanical ventilation system can provide the airflow pattern,ventilation volume and comfort requirements required by the ward design process.However,a ward ventilation design that meets the norms or standards may not be able to cope with the microbial a erosol pollution in wards well.Therefore,it is necessary to study the microbial aerosol diffusion pattern and airflow organization optimization in wards.A full-scale experiment using Bacillus subtilis and computational fluid dynamics were utilized to model the microbial aerosol characteristics in a two-bed hospital ward with a constant air change rate(12 ACH).The results indicated that the microbial aerosol removal efficiency of unilateral downward ventilation was 50%higher than that of bilateral downward ventilation.Additionally,health care workers(HCWs)and nearby patients had lower breathing zone concentrations in the ward with unilateral downward ventilation.Furthermore,a partition played a posit ive role in protecting patients by reducing the amount of microbial aerosol exposure.However,no obvious protective effect was observed with respect to the HCWs.Only10% of the microbial aerosol was deposited on the surfaces in the ward with unilateral downward ventilation,while up to 35% of the microbial aerosol was deposited on the surfaces in the ward with bilateral downward ventilation during the900 s.The main deposition locations of the microbial aerosol were near the wall on the same side of the room as the patient’s head in all cases.Based on the experimental results,simulation results and comparative verification in the ward,this study conducted in-depth exploration for the airflow optimization organization in the ward.The influence of the airflow patterns of stratum ventilation and downward ventilation on the air velocity of patients and health care workers in the breathing zone was discussed.The effects of different air outlet positions and increased air changes on pollutant removal efficiency and deposition distribution were compared and analyzed.The results show that the stratum ventilation with the lower side return air is the best air supply in this study for removing microbial aerosols which also has much better protection to health care workers.In the working conditions involved in this study,the lower side return air condition has a better pollutant removal effect than the upper side return air condition of the same ventilation type.The microbial aerosol removal rate of the lower side return air in the downward ventilaiton and the stratum ventilation cases is about 15%and 55% higher than that of the upper side return air cases,respectively.In addition,increasing the number of air changes in the ward does not necessarily lead to better microbial aerosol removal effect.This study could provide scientific evidence for controlling cross-infection in hospital wards,as well as several guidelines for the disinfection of hospital wards.