scholarly journals Tracer gas is a suitable surrogate of exhaled droplet nuclei for studying airborne transmission in the built environment

2020 ◽  
Vol 13 (3) ◽  
pp. 489-496 ◽  
Author(s):  
Zhengtao Ai ◽  
Cheuk Ming Mak ◽  
Naiping Gao ◽  
Jianlei Niu
Keyword(s):  
Built Environment ◽  
Tracer Gas ◽  
Airborne Transmission ◽  
Droplet Nuclei

scholarly journals Characteristics of airborne transmission under stratum ventilation

2019 ◽  
Vol 111 ◽  
pp. 02019
Author(s):  
Tao Huang ◽  
Zhengtao Ai ◽  
Arsen Melikov
Keyword(s):  
Air Distribution ◽  
Breathing Zone ◽  
Relative Positioning ◽  
Exposure Risk ◽  
Tracer Gas ◽  
Airborne Transmission ◽  
Climate Chamber ◽  
Distribution Method ◽  
Close Proximity ◽  
Droplet Nuclei

The objective of this study is to investigate the characteristics of airborne spread of exhaled droplet nuclei between two occupants in a space conditioned by a horizontal air distribution method, known as stratum ventilation. Experiments were conducted in a full-scale climate chamber. Two breathing thermal manikins were used to simulate a standing infected person and a standing exposed person, respectively. Tracer gas (N2O) was added into the air exhaled by the infected manikin. The tracer gas concentrations in the air inhaled by the exposed manikin and at the ventilation exhaust were continuously monitored. ACH was kept at 2 h-1. The variables in the experiments include the positioning of the manikins, the distance between manikins, and the room air temperature. The horizontal supply airflow to the breathing zone strongly intensifies the mixing between the flow of exhalation and the room air, which reduces the exposure risk of occupants at close proximity and flattens the risk-distance curves. The homogenization of concentration weakens considerably the importance of the relative positioning and location of the infected and exposed persons. All those characteristics of airborne transmission may not be maintained, however, if the horizontal supply jet does not interact directly with the occupants. The findings from this study are intended to contribute for better understanding of airborne transmission indoors.

scholarly journals Airborne transmission during short-term events under stratum ventilation

2019 ◽  
Vol 111 ◽  
pp. 01098
Author(s):  
Kaho Hashimoto ◽  
Zhengtao Ai ◽  
Arsen Melikov
Keyword(s):  
Steady State ◽  
Separation Distance ◽  
Control Measures ◽  
Exposure Index ◽  
Tracer Gas ◽  
Short Term ◽  
Airborne Transmission ◽  
Face To Face ◽  
Droplet Nuclei

Past studies on airborne spread of expiratory droplet nuclei between occupants were focused on long-term exposure under steady-state conditions. However, exposure during short-term events can be widely found in practice, e.g. medical examination or short meeting. Airborne transmission during short-term events under stratum ventilation was examined experimentally in this study. Two breathing thermal manikins were employed to simulate a standing infected person and a standing exposed person. The manikins were placed face-to-face and face-to-back to reproduce the exposure conditions with the highest and the lowest risk, respectively. Tracer gas was dosed into the air exhaled by the “infected” manikin to simulate the droplet nuclei. A newly developed average exposure index was used to evaluate the exposure risk. The time-averaged exposure index increases over time, but the increasing rate depends strongly on the duration of exposure time, e.g., the exposure index increases much faster during the first 5 minutes than during the period after 5 minutes. The exposure index during short-term events does not always decrease with the increase of separation distance. These findings imply that the control measures formulated based on steady-state conditions are not necessarily effective to short-term events.

scholarly journals Peering inside a cough or sneeze to explain enhanced airborne transmission under dry weather

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kai Liu ◽  
Majid Allahyari ◽  
Jorge S. Salinas ◽  
Nadim Zgheib ◽  
S. Balachandar
Keyword(s):  
High Fidelity ◽  
Substantial Variation ◽  
Ambient Conditions ◽  
Airborne Transmission ◽  
Social Distancing ◽  
Virtual Experiments ◽  
Long Time ◽  
Simulation Results ◽  
High Fidelity Simulations ◽  
Droplet Nuclei

AbstractHigh-fidelity simulations of coughs and sneezes that serve as virtual experiments are presented, and they offer an unprecedented opportunity to peer into the chaotic evolution of the resulting airborne droplet clouds. While larger droplets quickly fall-out of the cloud, smaller droplets evaporate rapidly. The non-volatiles remain airborne as droplet nuclei for a long time to be transported over long distances. The substantial variation observed between the different realizations has important social distancing implications, since probabilistic outlier-events do occur and may need to be taken into account when assessing the risk of contagion. Contrary to common expectations, we observe dry ambient conditions to increase by more than four times the number of airborne potentially virus-laden nuclei, as a result of reduced droplet fall-out through rapid evaporation. The simulation results are used to validate and calibrate a comprehensive multiphase theory, which is then used to predict the spread of airborne nuclei under a wide variety of ambient conditions.

Role of ventilation in airborne transmission of infectious agents in the built environment ? a multidisciplinary systematic review

Indoor Air ◽  
2007 ◽  
Vol 17 (1) ◽  
pp. 2-18 ◽  
Author(s):  
Y. Li ◽  
G. M. Leung ◽  
J. W. Tang ◽  
X. Yang ◽  
C. Y. H. Chao ◽  
...  
Keyword(s):  
Systematic Review ◽  
Built Environment ◽  
Infectious Agents ◽  
Airborne Transmission

Measuring interpersonal transmission of expiratory droplet nuclei in close proximity

2021 ◽  
pp. 1420326X2110296
Author(s):  
Linzhi Fu ◽  
Peter V. Nielsen ◽  
Yi Wang ◽  
Li Liu
Keyword(s):  
Disease Transmission ◽  
Short Range ◽  
Close Contact ◽  
Measurement Techniques ◽  
Transmission Risk ◽  
Interpersonal Distance ◽  
Airborne Transmission ◽  
Face To Face ◽  
Close Proximity ◽  
Droplet Nuclei

Increasing evidence supports the significant role of short-range airborne transmission of viruses when in close contact with a source patient. A full-scale ventilated room (Cleanliness: ISO 14644–1 Class 5) and two face-to-face standing breathing thermal manikins were used to simulate a source individual and a susceptible person. Monodisperse particle generation and measurement techniques were used to evaluate the effect of virus-laden droplet nuclei size on short-range airborne transmission risk. We analysed four particle sizes (1.0, 1.5, 2.5, and 5.0 µm) to simulate the transport of exhaled droplet nuclei within an interpersonal distance of 0.5 m. The results indicated that the size distribution of airborne droplet nuclei could significantly influence transmission, with the inhalation fraction decreasing with increasing droplet nuclei size. Additionally, results showed that proximity to the source manikin could influence transmission. Inhalation fraction decreased with increasing interpersonal distance, fitting well with the 1/ d rule of droplet nuclei concentration decay. Our findings improve the understanding of the mechanism of the disease transmission.

scholarly journals The role of airborne transmission in a large single source outbreak of SARS-CoV-2 in a Belgian nursing home in 2020

2021 ◽  
Author(s):  
Bea Vuylsteke ◽  
Lize Cuypers ◽  
Guy Baele ◽  
Marianne Stranger ◽  
Sarah Lima Paralovo ◽  
...  
Keyword(s):  
Nursing Home ◽  
Index Case ◽  
Physical Contact ◽  
Single Source ◽  
Tracer Gas ◽  
Airborne Transmission ◽  
High Background ◽  
Cultural Event ◽  
Co2 Level

Abstract Objectives: To better understand the conditions which have led to one of the largest COVID-19 outbreaks in Belgian nursing homes in 2020. Setting: A nursing home in Flanders, Belgium, which experienced a massive outbreak of COVID-19 after a cultural event. An external volunteer who dressed as a legendary figure visited consecutively the 4 living units and tested positive for SARS-CoV-2 the next day. Within days, residents started to display symptoms and the outbreak spread rapidly within the nursing home. Methods: We interviewed key informants and collected standardized data from all residents retrospectively. A batch of 115 positive samples with a Ct value of <37 by qRT-PCR were analysed using whole-genome sequencing. Six months after the outbreak, ventilation assessment of gathering rooms in the nursing home was done using a tracer gas test with calibrated CO2 sensors. Results: Timeline of diagnoses and symptom onsets clearly pointed to the cultural event as the start of the outbreak, with the volunteer as index case. The genotyping of positive samples depicted the presence of one large cluster, suggesting a single source outbreak. The global attack rate among residents was 77% with a significant association between infection and presence at the event. Known risk factors such as short distance to or physical contact with the volunteer, and wearing of a mask during the event were not associated with early infection. The ventilation assessment showed a high background average CO2 level in four main rooms varying from 657 ppm to 846 ppm. Conclusions: Our investigation shows a rapid and widespread single source outbreak of SARS-CoV-2 in a nursing home, in which airborne transmission was the most plausible explanation for the massive intra-facility spread. Our results underscore the importance of ventilation and air quality for the prevention of future outbreaks in closed facilities.

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