Characteristics Of Human Droplet Contaminant And Transmission In Wards

The spread of respiratory diseases has been a hot topic concerned by different disciplines, the main route of transmission is droplet or airborne transmission, contaminant sources are mainly from respiratory patients through breathing, speaking, coughing, sneezing and other respiratory activities.Hospital is the main place of the spread of respiratory diseases with the phenomena of crossing infection between patients andserious infection by medical staff.Therefore, taking reasonable means to control the spread of respiratory disease is particularly important.Based on the National Natural Science Foundation Project “Research on the basic issues of health comfort effects of thermal and humid environment in hospital buildings”(No.51278506), this paper researches the characteristics of the human droplet contaminant sources and contaminant transmission in the hospital wards, which provides theoretical basis for prevention and controling the spread of the respiratory disease and the evidence for ventilation design.Firstly, the microbial contaminant sources in the ward and its harmfulness are analyzed. Through literature research method, the characteristics of droplet contaminant from persons are summarized,including its generation mechanism, droplet size, concentration distribution, velocity distribution, etc. It can be concluded that droplet size range of health people is 0.1 to 10μm, the droplet nuclei range is 0.01 to 5μm, while thedroplet size range of patients is 0.05 to 10μm.The relationship of the droplet concentration is coughing>speaking>breathing and respiratory patients produce more droplet concentration than health people. Meanwhile, this paper analyses the main ways to spread the contaminant and the physical properties such as evaporation and attenuation during the progress.Through field investigation way, the treatment pattern and personnel structure are known. This paper analyses the number of people in wardin different departments and hospitals. Furthermore, the personal flow model in ward is established and the values of the parameters are determined by the survey data. Combined with the human droplet contaminant characteristics, the amount of the human droplet contaminant in the ward isdetermined.Then, the hospital ward network diagram is set by the knowledge ofgraph theory and the branch resistance value is determined.According to the node flow equilibruim,single circle pressure balance and the contaminant mass conservation, the network flow modeland concentration model are set and solved by Newton iteration Method. The new developed model is verified by theexperimentaldata from literature.Finally, taking the respiratory wardin Chongqing as an engineering case,this paper draws the network diagram of natural ventilation and mechanical ventilation and establishes the network flow model and the concentration model for ward and gets the concentration change of different regionswith time. It can be concluded that the contaminantconcentration in the ward is greater than other auxiliary rooms and the contaminantconcentrationin the ward is in accord with the patient number; The contaminantconcentration in the ward is mainly affected by the amount of patients’ contaminant sources;The contaminantconcentration in the ward decreases 21.5% once the ACH increases one times; When disease outbreaks in two hours, it’s better to isolate the pollution sources and increase three times of ventilation rate when dilution to the baseline concentration in two hours.