Moderately high concentrations of carbon dioxide (CO2) indoors can significantly impair people’s decision-making performance, according to new research.
“In our field we have always had a dogma that CO2 itself, at the levels we find in buildings, is just not important and doesn’t have any direct impacts on people,” said William Fisk, Ph.D., a co-author of the study and a scientist in the Department of Energy’s Lawrence Berkeley National Laboratory.
“So these results, which were quite unambiguous, were surprising.”
The study, conducted with researchers from State University of New York Upstate Medical University, found that test subjects showed “significant” reductions on six of the nine scales of decision-making performance at CO2 levels of 1,000 parts per million (ppm) and “large” reductions on seven of the scales at 2,500 ppm.
The most dramatic declines in performance, in which subjects were rated as “dysfunctional,” were for taking initiative and thinking strategically, according to the researchers.
Mark Mendell, Ph.D., a co-author of the study, said the findings are startling, noting that previous studies looked at 10,000 ppm and 20,000 ppm. “That’s the level at which scientists thought effects started,” he said.
The researchers note that while the results need to be replicated in a larger study, the findings point to possible economic consequences of pursuing energy-efficient buildings without regard to occupants.
“As there’s a drive for increasing energy efficiency, there’s a push for making buildings tighter and less expensive to run,” said Mendell. “There’s some risk that, in that process, adverse effects on occupants will be ignored.
“One way to make sure occupants get the attention they deserve is to point out adverse economic impacts of poor indoor air quality. If people can’t think or perform as well, that could obviously have adverse economic impacts.”
The primary source of indoor CO2 is humans. While typical outdoor concentrations are around 380 ppm, indoor concentrations can go up to several thousand ppm. Higher indoor CO2 concentrations are due to low rates of ventilation, which are often driven by the need to reduce energy consumption.
In the real world, CO2 concentrations in office buildings normally don’t exceed 1,000 ppm, except in meeting rooms, when groups of people gather for extended periods of time, the researchers explain. In classrooms, concentrations frequently exceed 1,000 ppm and occasionally exceed 3,000 ppm, they add.
Federal guidelines set a maximum occupational exposure limit at 5,000 ppm as a time-weighted average for an eight-hour workday.
Fisk said he decided to test the conventional wisdom on indoor CO2 after coming across two small Hungarian studies reporting that exposures between 2,000 and 5,000 ppm may have adverse impacts on human activities.
The research team assessed CO2 exposure at three concentrations: 600, 1,000 and 2,500 ppm. They recruited 24 participants, mostly college students, who were studied in groups of four in a small office-like chamber for 2.5 hours for each of the three conditions.
Ultrapure CO2 was injected into the air supply and mixing was ensured, while all other factors, such as temperature, humidity, and ventilation rate, were kept constant, the researchers note. The sessions for each person took place on a single day, with one-hour breaks between sessions.
Although the sample size was small, the results were unmistakable, according to the researchers.
“The stronger the effect you have, the fewer subjects you need to see it,” Fisk said. “Our effect was so big, even with a small number of people, it was a very clear effect.”
The study used a test that assesses decision-making performance, called the Strategic Management Simulation (SMS) test. In most studies of how indoor air quality affects people, test subjects are given simple tasks to perform, such as adding a column of numbers or proofreading text.
“It’s hard to know how those indicators translate in the real world,” said Fisk. “The SMS measures a higher level of cognitive performance, so I wanted to get that into our field of research.”
The SMS is mostly commonly used to assess effects on cognitive function, by drugs, pharmaceuticals or brain injury, as well as a training tool for executives. It gives scenarios — for example, you’re the manager of an organization when a crisis hits, what do you do? — and scores participants in nine areas.
“It looks at a number of dimensions, such as how proactive you are, how focused you are, or how you search for and use information,” said Fisk. “The test has been validated through other means, and they’ve shown that for executives it is predictive of future income and job level.”
The next step for the Berkeley Lab researchers is to reproduce and expand upon their findings.
“Our first goal is to replicate this study because it’s so important and would have such large implications,” said Fisk. “We need a larger sample and additional tests of human work performance. We also want to include an expert who can assess what’s going on physiologically.
“Assuming it’s replicated, it has implications for the standards we set for minimum ventilation rates for buildings,” he continued. “People who are employers who want to get the most of their workforce would want to pay attention to this.”
Funding for the study, which was published in Environmental Health Perspectives, was provided by SUNY and the state of New York.