J. Biomedical Science and Engineering, 2010, 3, 653-663 JBiSE doi:10.4236/jbise.2010.37089 Published Online July 2010 (http://www.SciRP.org/journal/jbise/ ). Published Online July 2010 in SciRes. http://www.scirp.org/journal/jbise Modelling infection spreading control in a hospital isolation room Carla Balocco, Pietro Liò 1 Department of Energy Engineering “Sergio Stecco”, Firenze, Italy; 2 Computer Laboratory, University of Cambridge, Cambridge, UK. Email: pl219@cam.ac.uk Received 9 May 2010; revised 21 May 2010; accepted 27 May 2010. ABSTRACT This paper investigates the airflow patterns con- nected 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 simula- tions of air pattern diffusion and air velocity field, provided by the existing typical HVAC primary air system designed for infectious patients, were per- formed using CFD. A multiphysics approach, com- bined Convection-Conduction, Incompressible Na- vier-Stokes models on non-isothermal air flow and Convection-Diffusion, was used. Simulations results highlighted that the flow field and velocity distribu- tion induced by the high turbulence air inlet diffuser combined with the air return diffusers produce wide recirculation zones near the wall and partial stagna- tion 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 recir- culation zones which can harbour lingering patho- gens. Keywords: Airborne Diffusion; Hospital Anfection; VAV System; Transient Simulation; CFD 1. INTRODUCTION The risk of virus particles dispersal in hospitals mainly depends on airflow patterns and on airflow directions changes caused by people’s activity, e.g. moving or opening doors. The ventilation system of isolation rooms, operating under closed-door conditions is crucial if the viruses spread and infection must be contained. The quality of the hospital environment is provided by an efficient air-conditioning and ventilating system design, in controlling temperature, humidity, pressure, and in- door air quality. The Heating Ventilation Air Condition- ing systems (HVAC) design is fundamental to maintain negative pressure within isolation rooms, to protect heal- th of workers, patients and visitors. This is also neces- sary to control patient risk from airborne diseases. In recent years few works have focused on computa- tional models using fluid dynamics approaches to inves- tigated airflow patterns and the related spreading of in- fection in isolation rooms for different ventilation sys- tems (for example operating under open or closed-door conditions) [1-4]. The main attention of these papers has been the evaluation of the effects of negative pressure in isolation rooms accommodating patients with highly infectious diseases. Recent studies have highlighted that an air velocity above 0.2 m s -1 via a doorway effectively prevents the spread of airborne contaminants out of the isolation room in the state of door opening [3,5]. HVAC switch on-off impact on virus and bacteria load has widely investigated recently [6-10]. Techniques such as aerosol particle tracer sampling and computational fluid dynamics can be applied to study the performance of ventilation systems during coughing episodes [4]. HVAC operating for hospitals, must establish optimal airflow pattern inside isolation rooms for infective and in particular for immune- suppressed patients, such that clean air from the air- supply vents may carry the air across infectious sources, and then flow through the exhaust vents completely [2,3]. However, it is not sufficient to provide clean environ- ments, due to the higher cross-infections risk, useful guidelines on public health strategies and management can be obtained studying the risky environments by CFD-FEM simulation. In particular CFD simulations based on multiphysics approach can provide a good pre- dictive efficacy, since the possibility to achieve in hos-