Estimation of the number of people under controlled ventilation using a CO&lt;inf&gt;2&lt;/inf&gt; concentration sensor

Kawauchi

Yokogawa

et al. 2021

Preprint

We experimentally investigated indoor air ventilation using the CO2 tracer technique to verify the infection cluster of SARS-CoV-2 that erupted at an office space. Multi-placed observations revealed extremely low air change rates (0.1/h) at the site. The local infection clusters were observed several meters away from a door that is the only ventilation in the office, which suggests a negative effect of plastic sheeting shielding. The thermo-fluid simulation showed that the plastic sheet blocked the airflow and trapped the exhaled air in each partition cell. As risk suppression methods, improving air ventilation by opening windows and using fans were verified, and significant improvements (10-28/h) were observed for each partition cells.

Section: Methodsmentioning

confidence: 99%

Experimental investigation to verify if excessive plastic sheeting shielding produce micro clusters of SARS-CoV-2

Kawauchi

Yokogawa

et al. 2021

Preprint

“…where 𝐶𝐶 𝑡𝑡 is the concentration of indoor pollutants at time 𝑑𝑑 , 𝑀𝑀 is the number of pollutants generated, 𝜆𝜆 is the air ventilation rate, and 𝐶𝐶 0 is the concentration in the absence of pollutant sources. As a general solution to the first-order linear ordinary differential equation shown in Equation ( 1), the concentration of pollutants at time 𝑖𝑖 can be obtained by the Seidel's equation 12,13 :…”

Section: Methodsmentioning

confidence: 99%

“…The stable mass balance of well-mixed air can be described as: where C t is the concentration of indoor pollutants at time t, M is the number of pollutants generated, λ is the air ventilation rate, and C 0 is the concentration in the absence of pollutant sources. As a general solution to the first-order linear ordinary differential equation shown in Equation (1), the concentration of pollutants at time i can be obtained by the Seidel’s equation 12,13 : where Q is the outdoor air supply around the sensors [m 3 /h], V is the effective volume of the space around the sensors, s is the time at which the observation started, and λ = Q / V is the assumed air ventilation rate. When no pollutants are generated, i.e.…”

Section: Methodsmentioning

confidence: 99%

Prevention of SARS-CoV-2 airborne transmission in a workplace based on CO2 sensor network

Yokogawa

Kitamura

et al. 2022

Preprint

We measured the compartmental air change per hour (ACH) using a CO2 sensor network in an office space where a cluster of COVID-19 infections attributed to aerosol transmission occurred. Generalized linear mixed models and dynamic time warping were used for a time series data analysis, and the results indicated that the ventilation conditions were poor at the time of the cluster outbreak, and that the low ACH in the room likely contributed to the outbreak. In addition, the adverse effects of inappropriate partitions and the effectiveness of ventilation improvements were investigated in detail. ACH of less than 2 /h was considered a main contributor for the formation of the COVID-19 cluster in the studied facility.

“…Based on the data measured by the CO 2 sensor, the ventilation frequency was estimated using Seidel’s formula 2, 3 : …”

Section: Methodsmentioning

confidence: 99%

Workplace ventilation improvement to address coronavirus disease 2019 cluster occurrence in a manufacturing factory

Kitamura

Ohashi

et al. 2022

Preprint

Aim and MethodsA coronavirus disease 2019 (COVID-19) cluster emerged in a manufacturing factory in early August 2021. In November 2021, a ventilation survey using tracer gas and data analysis was performed to reproduce the situation at the time of cluster emergence and verify that ventilation in the office increased the risk of aerosol transmission; verify the effectiveness of measures implemented immediately in August; and verify the effectiveness of additional measures when previously enforced measures proved inadequate.ResultsAt the time of cluster emergence, the average ventilation frequency was 0.73 times/h, less than the 2 times/h recommended by the Ministry of Health, Labour, and Welfare; as such, the factory’s situation was deemed to have increased the risk of aerosol transmission. Due to the measures already taken at the time of the survey, the ventilation frequency increased to 3.41 times/h on average. It was confirmed that ventilation frequency increased to 8.33 times/h on average, when additional measures were taken.ConclusionTo prevent the re-emergence of COVID-19 clusters, it is necessary to continue the measures that have already been implemented. Additionally, introduction of real-time monitoring that visualizes CO2 concentrations is recommended. Furthermore, we believe it is helpful that external researchers in multiple fields and internal personnel in charge of health and safety department and occupational health work together to confirm the effectiveness of conducted measures, such as this case.