CO2 concentration monitoring inside educational buildings as a strategic tool to reduce the risk of Sars-CoV-2 airborne transmission

Abstract

In order to avoid SARS-CoV-2 transmission inside educational buildings and promote the safe reopening of schools, the Italian Government, in line with the other European countries and in accordance with the WHO recommendations, adopted a contingency plan including actions able to guarantee adequate air ventilation in classrooms. Therefore, in this pilot study, a surveillance activity based on the real-time monitoring of CO 2 levels as a proxy of SARS-CoV-2 transmission risk, was conducted inside 9 schools (11 classrooms) located in Apulia Region (South of Italy) during the reopening of schools after the lockdown due to COVID-19 pandemic. More specifically, monitoring activities and data treatment were conducted to evaluate the initial scenario inside the classrooms (first stage of evaluation) and the potential improvements obtained by applying a detailed operating protocol of air ventilation based on specific actions and the simultaneous real time visualization of CO 2 levels by non-dispersive infrared (NDIR) sensors (second stage of evaluation). Although, during the first evaluation stage, air ventilation through the opening of windows and doors was guaranteed, 6 (54%) classrooms showed mean values of CO 2 higher than 1000 ppm and all classrooms exceeded the recommended CO 2 concentration limit value of 700 ppm. The development and implementation of tailored ventilation protocol including the real time visualization of CO 2 levels allowed to depict better scenariosAn overall improvement of CO 2 levels was indeed registered for all classrooms where teachers were compliant and helpful in the management of the air ventilation strategy. Therefore, this study reports the first evidence-based measures demonstrating that, with the exception of few environments affected by structural limits, the real-time visualization and monitoring of CO2 concentrations allowes effective air exchanges to be implemented and contributes to prevent SARS-CoV-2 transmission. Moreover, on the basis of the monitoring outcomes and in order to ensure adequate air ventilation in educational buildings, a 4 level-risk classification including specific corrective actions for each level was provided.

Recent Insights into the Measurement of Carbon Dioxide Concentrations for Clinical Practice in Respiratory Medicine

“…Measuring atmospheric CO 2 concentrations has been helpful for evaluation of the ventilation conditions in rooms of buildings aiming to decrease the transmission risk of SARS-CoV-2, which can cause COVID-19 ( Figure 3 ) [ 5 , 21 , 22 ]. Smaller droplets (<10 μm) with SARS-CoV-2 content expired from COVID-19 patients can travel tens of meters in the air while indoors and cause airborne transmission [ 23 , 24 ].…”

Rapid evidence review to inform safe return to campus in the context of coronavirus disease 2019 (COVID-19)

“…Whilst CO 2 levels can be used to approximate the risk of COVID-19 transmission 39 , they are only a proxy for this risk. With that caveat, some authors have suggested that CO 2 levels might be used strategically in negotiations with employers 40 . Figure 3 shows some suggested cut-off levels for denoting “low risk” (below 700 ppm), “medium risk” (700–800 ppm), “high risk” (800–1000 ppm) and “very high risk” (>1000 ppm), though other publications recommend slightly different cut-offs for these categories.…”

The role of outdoor and indoor air quality in the spread of SARS-CoV-2: Overview and recommendations by the research group on COVID-19 and particulate matter (RESCOP commission)

“…In this perspective, the added value of specific systems for Indoor Air Quality monitoring needs further research. Di Gilio et al (2021) , validated that CO 2 portable monitors (10 cm × 10cm) can be used to assess the potential risk of infected droplets/aerosols inhalation when CO 2 levels reach a defined threshold (fixed at 700 ppm in more recent studies) and foster the natural ventilation of the space by simply opening doors and windows for the time needed to reduce CO 2 levels. Of note, normal breathing of a child aged 7–9 years old generates 14 L of CO 2 per hour, which is 50% lower than the amount produced by a teenager, while in conditions of moderate physical activity, a 15 years old student can release up to 85 L of CO 2 per hour.…”