scope:

INTRODUCTION

Air movement in indoor environments is strongly linked to the transmission and spread of airborne infectious diseases, such as measles, tuberculosis, chickenpox, influenza, smallpox, and SARS (Li et al. 2007). The lack of knowledge of and insufficient data on ventilation requirements in hospitals, schools, and offices make it difficult to understand the spread of airborne infectious diseases (Li et al. 2007; Beggs et al. 2008). A study by Yin et al. (2009) showed that ventilation systems played a very important role in the transmission of exhaled particles from a patient to a caretaker in the same ward. They showed that displacement ventilation can provide much better indoor air quality than overhead mixing ventilation. The ventilation effectiveness of a displacement ventilation system with a reduced ventilation rate of 4 ach can be the same as that of an overhead mixing ventilation system with a ventilation rate of 6 ach. However, there were concerns about whether an object moving, such as a visitor or caretaker walking, changing a sheet on the patient's bed, or a swinging entrance door in an inpatient ward, could destroy the stratified flow created by the displacement ventilation and thus decrease the ventilation effectiveness (Brohus et al. 2006; Bjørn and Nielsen 2002; Bjørn et al. 1997). Mazumdar (2009) found that a moving passenger in an aircraft cabin could carry a contaminant in his or her wake to positions far from the contaminant source. Thus, it is essential to assess the impact of moving objects on contaminant transmission in inpatient wards with displacement ventilation.