Using Carbon Dioxide To Estimate Indoor Workplace Air Quality

As workers and employers attempt to navigate and negotiate to return to in-person work or not with the Covid pandemic continuing, increased attention is being paid to indoor air quality. It’s a complicated and interesting topic with real implications for individual and community health. One interesting aspect of this topic is the potential to use CO2 monitors to attempt to measure indoor air quality.

Indoor air quality can vary widely depending on building ventilation and other factors. Standards for ventilation within buildings have changed over time. The United States Environmental Protection Agency?offers some interesting background:

“In the early and mid-1900s, building ventilation standards called for approximately 15 cubic feet per minute (cfm) of outside air for each building occupant, primarily to dilute and remove body odors. As a result of the 1973 oil embargo, however, national energy conservation measures called for a reduction in the amount of outdoor air provided for ventilation to 5 cfm per occupant. In many cases, these reduced outdoor air ventilation rates were found to be inadequate to maintain the health and comfort of building occupants.”

As this background suggests, the situation is more complicated than just “newer buildings have better ventilation.” It’s also the case that some buildings may have had their heating ventilation and cooling (HVAC) systems upgraded – especially in response to Covid.

So how to even begin to gauge indoor air quality in a specific space? Carbon dioxide meters are one tool that can be used to begin to get a handle on this issue.?

Humans exhale carbon dioxide (CO2) when they breathe, so measuring the level of carbon dioxide build-up in a space is a decent proxy for measuring how much of people’s exhalations are remaining in a particular space. Carbon dioxide meters are readily commercially available starting at costs of less than one hundred dollars.

The background level of carbon dioxide in the atmosphere is 350-450ppm, so numbers significantly above this on a CO2 meter in an occupied space could indicate poor ventilation.?

There are several things to consider when taking the measurement to be sure the measurement is accurate, as?Rich Prill from the Washington State University Extension Energy Program?explains:

“Meaningful assumptions about ventilation rate based on CO2 values require the building or zone to be occupied long enough to allow the CO2 levels to reach a balance with the ventilation rate. This balance is known variously as equilibrium, unity, or steady-state. In an occupied building with a very low ventilation rate, the CO2 levels will likely continue to increase throughout the day, never reaching a steady-state concentration. On the other hand, buildings with an aggressive ventilation rate and good mixing of the outside air may prevent CO2 from accumulating much beyond outdoor levels—resulting in low CO2 concentrations throughout the day. Unless this steady-state or equilibrium has been reached, the building ventilation rate can be overestimated.”

So, now that we have an idea of how to take the measurement, how high is too high? Prill further explains:

“Using CO2 as an indicator of ventilation, ASHRAE [American Society of Heating,

Refrigeration, and Air Conditioning Engineers] have recommended indoor CO2

concentrations are maintained at—or below—1,000 ppm in schools and 800 ppm in

offices.”

High levels of CO2 can be detrimental on their own, and CO2 can be a somewhat effective sign of overall ventilation quality in an indoor space. But do CO2 levels correlate perfectly with Covid safety in a space? No. Not perfectly.?

There are?several important caveats?to the idea of using CO2 levels as a proxy for Covid safety in space. Having said that, though, CO2 levels – although not a perfect tool to measure Covid safety in an indoor space – can be?an important and useful proxy?to get an idea of ventilation quality in an indoor space and approximate Covid safety in that space as well.

Additionally, the relatively ready availability and affordability of CO2 monitors can make them a practical choice. Employers can use CO2 monitors proactively to ensure their workspaces are well ventilated. And workers can use them to check the ventilation of their own workspaces.

Article Link - Using Carbon Dioxide To Estimate Indoor Workplace Air Quality

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Author - Staff Writer

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