Study On Control Of Biological Particle Transmission Under Different Ventilation Strategies

Transmission of airborne bacteria is the main factor causing surgical site infection (SSI), which is harmful to patient's health and even life, and would cause great economical burden. Previous research results have showed evidence of relationships between cleanness of room air and incidence of SSI. This paper focuses on the control strategies of airborne transmission of bacteria in operating room using filed test data and computational method.Bacteria collecting agar dishes were put in different places of the two operating rooms to get the deposited bacteria number during the operation. Then numerical simulation was carried out to calculate particle trajectories using the Euler-Lagrange approach. Simulation results were compared with field measured data, and acceptable level of consistency was found. Analysis showed that surgical lamps can induce turbulence, which may bring bacteria-carrying-particles to the surgical site causing potential SSI. We compared CFU (colony forming unit) deposition onto the"critical area", which consisted of three connected areas around surgical site on patient body.There is a particle deposition drop of 86.9% from classâ…¡to classâ… operating room. Under same air change rate, we found lower supply air velocity would reduce the particle deposition on upper critical surface, and increase particle concentration around the patient. And in the comparison between different supply air velocities, we found 0.25m/s is a turning point, which has the lowest particle deposition in this classâ…¡operation room. So we propose that in the evaluation of control abilities of different air flow patterns, particle deposition rate should be taken into consideration.In the model of partial horizontal air supply unit, velocity decrease is about 40% to 50%. Under same air change rate, the particle deposition in horizontal air supply is 65% less than that in vertical supply model. In the model of whole room partial horizontal supply system, no particle deposition was found, which is the most desired. At the same time, in the two kinds of horizontal supply system, particle concentration around surgical staffs is higher than that in vertical supply systems. The correctness of these results should be further verified by experimental method.In the dynamic simulation, sub-air-flow caused by movement of nurses is limited to three times width of the nurse under a walking velocity of 1m/s. Nurses'movement was found has minimal influence on the particle concentration around the surgical site, and not obvious increase was found of particle deposition on the critical area.