Ordinary carbon dioxide exposures inside classrooms, offices or bedrooms could harm your health and even impact decision-making
Exposure to as low as 1,000 ppm can cause health problems, a threshold that is already exceeded in many indoor environments with increased room occupancy and poor ventilation, warn researchers
Indoor levels of carbon dioxide - found in bedrooms, offices, and classrooms - could cause severe risks to human health, and have adverse impacts on the body, including kidney, bone problems, inflammation, and reduced decision-making abilities.
While climate change is recognized as a substantial threat to human health, few studies have focused on the direct human health effects of increased exposure to common/indoor carbon dioxide. However, according to a new study, there is growing evidence that suggests exposure to as low as 1,000 parts per million (ppm) can cause health problems, a threshold that is already exceeded in many indoor environments with increased room occupancy and poor ventilation. The researchers say that extended exposures to greater than 2,000 ppm can happen in poorly ventilated bedrooms, offices, and schools.
“In industrialized countries, people spend 80–90% of their time indoors, while vulnerable populations (including the elderly and the infirm) often spend entire days indoors. Indoor air quality is thus critical to public health,” says the study published in Nature Sustainability.
Study co-author Dr. Michael T. Hernke, from the University of Wisconsin–Madison, US, told MEA WorldWide (MEAWW) that exposures as low as 1,000 ppm for durations greater than 2.5 hours are concerning because these levels have been shown to affect higher-level cognitive abilities, such as decision-making performance.
“Acute health risks occur well below levels previously considered safe. Effects on cognition could be a ‘lagging’ indicator of unrecognized effects on human health, such as altered immune responses or subtle physiological effects. Such exposure levels are not uncommon indoors where people spend the vast majority of their time and will become more common if atmospheric carbon dioxide continues to build up,” says Dr. Hernke.
The review synthesized around 130 papers, 18 of which represent the core experimental findings that specifically focus on the health effects of carbon dioxide exposures. The study, says the team, is the most up-to-date systematic search of evidence for “environmentally relevant exposures of carbon dioxide and associated health risks.”
The research team focused on studies that considered carbon dioxide levels below 5,000 ppm because this is the workplace exposure limit for an 8-hour working day. According to their analysis, available evidence shows that common carbon dioxide exposures pose previously unrecognized human health risks.
“Emerging evidence supports the possibility that prolonged or chronic intermittent exposures to carbon dioxide - at concentrations below 5,000 ppm - pose direct risks to human health. These risks include inflammation, reduced higher-level cognitive abilities, bone demineralization, kidney calcification, oxidative stress, and endothelial dysfunction (inner lining of the small arteries fails to function normally),” says the study.
According to Dr. Hernke, typically, in occupied spaces that are well ventilated – carbon dioxide levels will average between 600 and 1,000 ppm. “However, being exposed to levels above 1,000 ppm is not uncommon – and prolonged exposures to greater than 2,000 ppm can occur in poorly ventilated bedrooms, offices, and schools. The established guidance, not always realized, of keeping carbon dioxide below 1,000 ppm in our living environments, is supported by the studies we reviewed,” Dr. Hernke told MEAWW.
He adds, “The concern is that as outdoor concentrations approach 1,000 ppm – it will become more difficult to maintain indoor concentrations below this level. An elevated background exposure level of 1,000 ppm – with acute spikes above 2,000 ppm – could adversely affect human health.”
According to the researchers, a review of some studies that investigated carbon dioxide concentrations in classrooms showed that all reported “median peak carbon dioxide values” above 1,000 ppm, with many above 2,000 ppm, suggesting widespread inadequate ventilation in schools. Brief exposures to elevated carbon dioxide are also routine in transit - for example, among participants in air-conditioned public transportation in Singapore, exposure levels of 1,300 ppm and spikes above 4,000 ppm for shorter intervals have been reported, says the research. Again, longer exposures to elevated carbon dioxide also occur on airplane flights, where levels have been found to exceed 1,000 ppm, and it can exceed 2,000 ppm during boarding time.
The researchers say that home and bedroom environments can also be significant sources of carbon dioxide exposure. “People spend nearly one-third of their life sleeping, and in industrialized societies, more than 60% of their time in their homes. Bedrooms can exceed 2,500 ppm when the doors are closed, the windows closed for energy conservation and the building ventilation reduced. When ventilation rates are normal, but the windows and bedroom doors are closed, carbon dioxide concentrations exceed 1,000 ppm, about 50% of the time,” says the study.
According to the research team, the main factors that increase carbon dioxide indoors are the number of occupants, because the carbon dioxide people exhale can build up in enclosed spaces, and the building ventilation rates. Another factor to consider, says the team, is how indoor spaces are cooled. “Closing windows and doors when the air-conditioning is used can reduce the intake of fresh air, which could allow carbon dioxide to accumulate in enclosed spaces with high occupant densities. Carbon dioxide, due to its density, can concentrate closer to the floor, away from the vents if they are up high – often in the ceiling,” says Dr. Hernke.
The study talks about yet another factor - which is the extent to which carbon dioxide emissions are hovering above dense urban environments, raising the outdoor concentrations that are used to refresh indoor air.
The research team says that the possibility that ordinary carbon dioxide exposures could impact health is extremely troubling and there is an urgent need to conduct more research on this topic and its implications for carbon emissions, and for the design and operation of indoor spaces. They recommend more studies to quantify the major sources of carbon dioxide exposure, to identify mitigation strategies to avoid adverse health effects and protect vulnerable populations and to fully understand the potential health effects of chronic or intermittent exposure to indoor air with higher carbon dioxide concentrations.
“Reasonable advice before all the facts are in would be to get more fresh air – by going outside more, and by making sure that your indoor spaces are properly ventilated. Buildings should promote the health and well-being of occupants – while energy and cost-savings should be optimized secondary to this condition being met. As carbon dioxide continues to build up in our atmosphere, driving more extreme weather events and elevated background concentrations, energy demands to maintain healthful indoor environments will increase. For example, adaptive measures like increasing use of air-conditioning and increasing building ventilation rates to dilute indoor-sourced pollutants, increase energy demands,” Dr. Hernke told MEAWW.