Think back to high school, during that last class of the day when heads start to drop. Everyone knows that feeling: You catch yourself falling asleep for an instant and waking up just before your head hits the desk.
Whether it’s down to more reasonable sleep schedules or the vast quantities of coffee drunk in modern offices, the situation rarely gets as bad for adults, but employees still frequently report feeling drowsy and lethargic toward the end of the day. That may be down to CO2 levels.
A 2015 study published in Environmental Health Perspectives examined the effects of indoor CO2 on office workers and found compelling evidence that higher concentrations led to decreased cognitive functioning. Researchers had employees spend six work days in an environment-controlled office in which they varied CO2 levels between 550 parts per million, 945 parts per million, and 1,400 parts per million.
To put those numbers in context, ambient air generally has a CO2 concentration of 380 parts per million, meaning that the lowest number represents a significant effort to scrub indoor air. The second category, 945 parts per million, is roughly the concentration you would expect to see in a regular office. At 1,400 parts per million, the last category might be seen in a particularly packed classroom at the end of the day.
Researchers asked participants in the study to complete a one and a half hour test at 3 pm each day to assess higher-order decision making. These tests were designed to be diverse, but simulate real-world challenges, like handling a township in the role of an emergency coordinator or mayor. Compared to the lowest CO2 levels, which researchers termed “Green +” conditions, participants performed 15 percent worse at 945 parts per million and a staggering 50 percent worse at 1,400 parts per million.
“What we found were quite shocking results,” the study’s leader, Harvard’s Joseph Allen, told The Washington Post. “Carbon dioxide at the concentrations we typically find indoors was long thought to be benign, but our understanding of this is changing. We’re starting to see that carbon dioxide has direct effects.”
Other research has indicated a connection between indoor CO2 levels and what is called “sick building syndrome”. Researchers estimated that an increase in ventilation sufficient to bring indoor levels of CO2 in line with outdoor levels could decrease the symptoms associated with sick building syndrome by 85 percent. This could potentially save employers significant money in decreased sick days and make employees more comfortable at work.
In the past, keeping track of indoor air quality was difficult and expensive, but modern advances have made CO2 monitors relatively inexpensive. The best systems are able to track CO2 concentration remotely, giving building teams access to real-time data in each tenant space or room. This metric can be used to help indicate the level of ventilation that will adequately refresh the air in each unit.
Armed with this information, building teams can make strategic decisions about how best to ventilate their buildings. An aggressive CO2 target, like the “Green +” level in the study above, will require more ventilation and so result in higher heating and cooling costs. Some tenants may prefer to eat these costs in order to keep their employees comfortable and productive. Under a less aggressive paradigm, CO2 sensors can help building teams to identify any over-ventilated spaces, which can then be adjusted to use less heating and cooling energy.
Installing and monitoring indoor CO2 levels is becoming increasingly common in green buildings. Certifications like LEED and WELL award points for buildings that monitor and act on real-time CO2 levels.
“These exposures should be investigated in other indoor environments, such as homes, schools, and airplanes, where decrements in cognitive function and decision-making could have significant impacts on productivity, learning, and safety,” Allen told the Post. “We spend 90 percent of our time indoors, yet we often ignore environmental quality as an important public health issue.”