Carbon dioxide monitoring is important as there is growing evidence that carbon dioxide levels in buildings and interior rooms correlate strongly with the airborne spread of diseases such as viruses and bacterial infection.1 Although there is no data linking carbon dioxide levels directly to viruses such as COVID-19, there is strong evidence now that high carbon dioxide levels in interior rooms is detrimental to health, lowers student performance and lowers productivity of employees.2 Elevated levels of carbon dioxide in rooms is commonly linked to inadequate ventilation and air exchanges which also enhance the potential of indoor transmission of disease. Essentially, high carbon dioxide levels act as a virtual canary in the coal mine. 3 4
Over the years, the focus has been primarily on air exchanges in rooms with minimal rates established by American Society of Heating, Refrigerating and Air-Conditioning Engineers of 2-3 air exchanges per hour in offices, 5-6 times per hour for schools, and 6-12 for hospitals.5 The primary reason for air exchanges is to eliminate the buildup of excess carbon dioxide. Each person exhales 5-8 liters of air per minute—air that has been in close context with lung tissues and also that has high levels of carbon dioxide. Crowded interior rooms such as classrooms with 20-30 people and other interior spaces with high occupancy are especially susceptible to buildups of carbon dioxide. Unfortunately, air exchanges, carbon dioxide levels calculated through carbon dioxide monitoring and particulate content within the air are generally unknown and unmonitored, leading to a host of issues and contributed to the significant interior spread of COVID-19 during the pandemic.6
New awareness of poor ventilation and the poor quality of interior space air generated through the pandemic is fueling new improvements in air quality and viral monitoring for indoor spaces to avoid the future catastrophic issues experienced within high occupancy spaces. Carbon dioxide monitoring is also becoming an important part of businesses’ operations.
At present, there are only a few countries (Taiwan, Norway and Portugal) that limit indoor carbon dioxide levels to 1000 parts per million (ppm), the maximum level recommended by Occupational Health & Safety. There is no universal criteria for the levels of carbon dioxide in the room, but it is generally known that levels above 2000 ppm are unacceptable as they are associated with headaches, sleepiness, poor concentration, loss of attention, increased heart rate and slight nausea. Research has now shown that standard ventilation rates are totally inadequate to allow for most interior spaces to meet optimal levels.7 In fact, opening windows is not really effective unless there is true cross ventilation. One cited example was a school in Montreal which opened its windows, but only exchanged half of its air in the room during an hour—considerably under the rate needed to avoid high carbon dioxide levels. That same room with mechanical ventilation had two air changes per hour, still inadequate but better than just opening the windows where there was no provision for effective cross-ventilation.8
In addition to poor air exchange regulations and awareness, most offices and classrooms are supplied with just 20 percent outside air through their HVAC system with the remaining 80 percent of air recirculated to save on energy consumption through heating and cooling. As a result, interior air is often just recirculated and can result in high buildups of carbon dioxide over the course of a day.
There are two issues here. One is to “filter” that recirculated air, but the second is to effectively improve the interior air quality through assuring that carbon dioxide levels are 1000 ppm or under and to assure that air exchange levels are improved. For example, it was found that a poorly ventilated hospital space with levels above 3000 ppm had an outbreak spread of tuberculosis which was then controlled when the carbon dioxide level was lowered to 600 ppm.9 Filtration can be improved by adding HEPA level filters or room air purifiers to trap many bacteria and viruses, but the filters will not improve the fundamental air quality level.
Filtration can be improved with AHU filters of MERV 13-16 or the use of portable air filters in the room. Ongoing detection of particulate in the room can then serve as a feedback loop that the filtration improvements are indeed working.10
The quality of interior air is a major issue for school age children and as the EPA states, “students are at a greater risk because of the hours spent in school facilities.”11 Air quality includes not only carbon dioxide levels tracked via carbon dioxide monitoring but also the relative humidity in a room as studies have shown that humidity levels of 40-60% inside rooms is necessary to minimize airborne transmission of diseases. Studies in California as well as Madrid, Spain2 have shown that there is a direct correlation between lack of ventilation and carbon dioxide levels with student performance and health. In fact, children are much more susceptible to health problems with poor air quality. Classrooms with lowered carbon dioxide levels were found to have a direct impact on math and reading scores in elementary schools as well as improved student response rates to color, picture, memory and word recognition in primary schools. Poor air quality with high carbon dioxide levels can often be associated with headaches, lethargy and sore throats. Poor air quality has also been linked to decreased attendance by staff and students while surveys have shown that 91% of parents believe that the quality of the air directly impacts the health of the students, showing there is wide support for improvements in this area.
Improvements in air quality and air filtration (whether primary or auxiliary) must start with effective carbon dioxide monitoring, increased levels of outside air mix and increasing oxygenation rates in interior spaces occupied by large groups of people.1
Opteev’s new ViraWarn Pro series, besides detecting airborne COVID-19 and influenza, will also feature a carbon dioxide sensor and a particulate sensor to help with the awareness as well as alerting to the detection of virus particles within an interior space. Armed with this information, schools can then take steps to improve air exchanges and outside air mixture as well as monitoring filtration strategies by recording airborne particulate levels. Continuous measurement of carbon dioxide levels in interior space, especially in classrooms, offices and lunchrooms is important to a viable healthy room strategy. For example, if a classroom is more than half capacity, many studies have indicated that the carbon dioxide level should not exceed 700ppm. However, it’s been found that many classrooms and other large occupancy spaces have frequently found carbon dioxide levels of 2800ppm and more.
Although classrooms, lunch areas, churches and offices are primary areas to check for a viable air quality program, there are other spaces that can have multiple people as occupants including restrooms and elevators where air quality should also be monitored and virus monitoring should occur.
Opteev’s new ViraWarn Pro series is an effective part of an overall air quality improvement as well as being an integral part of a BioViral Prevention Plan for a healthy return to schools, offices and other public places. For more information, contact us at [email protected] or call +1-443-457-1165.
1. Danlin Hou et al. “Bayesian Calibration of Using CO2 Sensors To Assess Ventilation Conditions and Associated COVID-19 Airborne Aerosol Transmission Risk in Schools.”, Concordia University, Montreal, Canada, January 2021
2. “Healthy air, healthier children.” Health and Environment Alliance, Brussells, Belgium, June 2019, www.env-health.org/wp-content/uploads/2019/06/Healthy-air-children_Madrid.pdf
3. “Why Indoor Air Quality is Important to Schools.” EPA, https://www.epa.gov/iaq-schools/why-indoor-air-quality-important-schools, accessed May 2021
4. RCPCH and Royal College of Physicians, “The inside story: Health effects on indoor air quality on children and young people.” RCPCH, https://www.rcpch.ac.uk/resources/inside-story-health-effects-indoor-air-quality-children-young-people, January 28, 2020
5. “The Standards for Ventilation and Indoor Air Quality.” ASHRAE, https://www.ashrae.org/technical-resources/bookstore/standards-62-1-62-2, accessed May 2021
6. Persily, A, and L de Jonge. “Carbon dioxide generation rates for building occupants.” Indoor air vol. 27, issue 5 (2017): 868-879. doi:10.1111/ina.12383
7. Jovan Pantelic & Kwok Wai Tham (2013) “Adequacy of air change rate as the sole indicator of an air distribution system’s effectiveness to mitigate airborne infectious disease transmission caused by a cough release in the room with overhead mixing ventilation: A case study.” HVAC&R Research, vol 19, issue 8 (2013): pp 947-961, DOI: 10.1080/10789669.2013.842447
8. Wilton, K. “12 Montreal teachers secretly tested classroom ventilation. The results are ‘problematic’.” Montreal Gazette, November 25, 2020. Accessed May 2021.
9. Barnhart, Scott MD, MPH; et al. “Tuberculosis in Health Care Settings and the Estimated Benefits of Engineering Controls and Respiratory Protection.” Journal of Occupational & Environmental Medicine, vol 39, issue 9 (September 1997): pp 849-854
10. ASHRAE Position Document on Filtration and Air Cleaning, ASHRAE, January 29, 2015, www.ashrae.org/file%20library/about/position%20documents/filtration-and-air-cleaning-pd.pdf
11. “Schools: Indoor Air Quality.” EPA, https://19january2017snapshot.epa.gov/schools-air-water-quality/schools-indoor-air-quality_.html, accessed June 2021