Carla Balocco, Pietro Liò

Abstract: This paper investigates the airflow patterns connected to different cough conditions, the effects of these arrangements on the regions of droplet fallout and dilution time of virus diffusion of coughed gas. We focus on some of the physical processes that occur in a double bed hospital isolation room, investigating the effect of the ventilation system on the spread of particles in air. A cough model was carried out and used for the numerical simulation of virus diffusion inside an existent isolation room. Transient simulations of air pattern diffusion and air velocity field, provided by the existing typical HVAC primary air system designed for infectious patients, were performed using CFD. A multiphysics approach, combined Convection-Conduction, Incompressible Navier-Stokes models on non-isothermal air flow and Convection-Diffusion, was used. Simulations results highlighted that the flow field and velocity distribution induced by the high turbulence air inlet diffuser combined with the air return diffusers produce wide recirculation zones near the wall and partial stagnation areas near the ceiling and between the two beds, but lower particle concentration in the room and their shorter spreading distance. This type of analysis is certainly cost effective to identify all the air recirculation zones which can harbour lingering pathogens.

Keywords: Airborne Diffusion; Hospital Anfection; VAV System; Transient Simulation; CFD

Cite this paper: Balocco, C. and Liò, P. (2010) Modelling infection spreading control in a hospital isolation room. Journal of Biomedical Science and Engineering, 3, 653-663. doi: 10.4236/jbise.2010.37089.

References

[1]   Tang, J., Li, Y., Eames, I., Chan, P. and Ridgway, G. (2006) Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises. Journal of Hospital Infection, 64(2), 100-114.

[2]   Zhao, B., Yang, C.Q., Chen, C., Chao F., Xu D.Y., Sun, L.C., Wei, G. and Li Y. (2009) How many airborne particles emitted from a nurse will reach the breathing zone/body surface of the patient in ISO Class-5 single-bed hospital protective environments? A numerical analysis. Aerosol Science and Technology, 43(10), 9901005.

[3]   Stanley, N.J., Kuehn, T.H., Kim, S.W., Raynor, P.C., Anantharaman, S., Ramakrishnan, M.A. and Goyal, S.M. (2008) Background culturable bacteria aerosol in two large public buildings using HVAC filters as long term, passive, high-volume air samplers. Journal of Environmental Monitor, 10(4), 474-481.

[4]   Eames, I., Shoabi, D., Klettner, C.A. and Taban, V. (2010) “Movement of airborne contaminants in a hospital isolation room,” Journal of the Royal Society Interface, 67576766.

[5]   Tunga, Y.-C., Hu, S.-C., Tsaia, T.-I. and Changa, I.-L. (2009) An experimental study on ventilation efficiency of isolation room. Building and Environment, 44(2), 271279.

[6]   Walker, J., Hoffman, P., Bennett, A., Vos, M., Thomas, M. and Tomlinson, N. (2007) Hospital and community acquired infection and the built environment – design and testing of infection control rooms. Journal of Hospital Infection, 65(Suppl 2), 43-49.

[7]   Soper, M. (2008) Pandemic ready, HVAC systems for worst-case scenarios. Health Facilities Management, 21(10), 49-52.

[8]   Bonetta, S., Bonetta, S., Mosso, S., Sampò, S. and Carraro, E. (2009) Assessment of microbiological indoor air quality in an Italian office building equipped with an HVAC system. Environmental Monitoring and Assessment, 161(1-4), 18-28.

[9]   Rygielski, L. and Uden, D. (2007) Creating comfort. Nine considerations for selecting the right hospital HVAC system. Health Facilities Management, 20(1), 19-23.

[10]   Grinshpun, S.A., Adhikari, A., Honda, T., Kim, K.Y., Toivola, M., Rao, K.S. and Reponen, T. (2007) Control of aerosol contaminants in indoor air: combining the particle concentration reduction with microbial inactivation. Environmental Science Technology, 15(41), 606-612.

[11]   Balocco, C., Liò, P. and Sani, L. (2010) Simulazione di un sistema di ventilazione per il controllo degli agenti eziologici nei reparti infettivi. Un caso reale. Condizionamento dell’ Aria Riscaldamento Refrigerazione, CdA n.1 febbraio.

[12]   Zhao, B., Zhang, Z. and Li, X.T. (2005) Numerical study of the transport of droplets or particles generated by respiratory systems indoors. Building and Environment, 40(8), 1032-1039.

[13]   Cunningham, E. (1910) On the velocity of steady fall of spherical particles through fluid medium. Proceedings of the Royal Society A, 83(561), 94-96.

[14]   www.comsol.com

[15]   (1995) UNI 10339, Air-conditioning systems for thermal comfort in buildings. General, classification and requirements. Offer, order and supply specifications. Italian Standard.

[16]   (2005) UNI EN 13779, Ventilation for non-residential buildings Performance requirements for ventilation and room conditioning systems. Italian Standard.

[17]   ASHARE-Handbook, HVAC-applications, SI, 1995.

[18]   (1991) ASHRAE. Health facilities. ASHRAE Handbook of Applications. S.I. Edition, Atlanta.