Abstract
The lavatory is a fertile area for the transmission of infectious disease through bioaerosols between its users. In this study, we built a generic compact lavatory model with a vacuum toilet, and computational fluid dynamics (CFD) is used to evaluate the effects of ventilation and user behaviors on the airflow patterns, and the resulting fates of bioaerosols. Fecal aerosols are readily released into the lavatory during toilet flush. Their concentration rapidly decays in the first 20 s after flushing by deposition or dilution. It takes about 315 s to 348 s for fine bioaerosols (<10 µm in diameter) to decrease to 5% of the initial concentration, while it takes 50 and 100 µm bioaerosols approximately 11 and <1 s, respectively, to completely deposit. The most contaminated surfaces by aerosol deposition include the toilet seat, the bowl, and the nearby walls. The 10 µm aerosols tend to deposit on horizontal surfaces, while the 50 and 100 µm bioaerosols almost always deposit on the bowl. In the presence of a standing thermal manikin, the rising thermal plume alters the flow field and more bioaerosols are carried out from the toilet; a large fraction of aerosols deposit on the manikin’s legs. The respiratory droplets generated by a seated coughing manikin tend to deposit on the floor, legs, and feet of the manikin. In summary, this study reveals the bioaerosol dilution time and the easily contaminated surfaces in a compact lavatory, which will aid the development of control measures against infectious diseases.
Highlights
The disease transmission by the lavatory inside built environments or mobile vehicles is a common and important routine
This study presented one specific compact lavatory model with a certain air distribution pattern
The time required to reduce the bioaerosols to 5% of the total bioaerosol mass after toilet flush was estimated to be approximately 315 s to 348 s for 1, 5, and μm bioaerosols, s for 50 μm bioaerosols, and 0.06 s for 100 μm bioaerosols
Summary
The disease transmission by the lavatory inside built environments or mobile vehicles is a common and important routine. Even when only a small group of people use aircraft toilets, most high-touch surfaces in an aircraft cabin are contaminated in 2 to 3 h, and most touchable surfaces are contaminated in 5 to 6 h [6] Because of such indirect transmission via fomites, decreasing the contact rate is a relatively more effective measure of reducing infection risk than is increasing the ventilation rate [4]. Particle image velocimetry and volumetric particle-streak velocimetry can be used to measure flow fields (such as in a cabin model), but these methods require that clear paths are available for optical measurement This necessitates modification of the geometric conditions of an aircraft lavatory model, meaning that the model no longer accurately represents a real aircraft lavatory, especially when a manikin is involved.
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