Infectious disease expert: Monitoring CO2 level in enclosed spaces reduces risk of COVID transmission

Samples of carbon dioxide monitors of different brands.

CEBU CITY, Philippines — Monitoring the carbon dioxide (CO2) level in the air may be the long-term solution to preventing COVID-19 transmission in establishments, schools, and workplaces.

International studies show that “the higher the CO2 levels, the faster the transmission,” says Doctor Bryan Lim, a Cebuano infectious disease expert who is currently serving as a consultant for the Emergency Operations Center (EOC) in Cebu City.

Lim said that he and some colleagues have also been studying the use of different brands and types of CO2 monitoring equipment that are placed in enclosed spaces to check if the same findings apply here.

Outcome of studies that were conducted earlier show that  COVID-19 has been proven to transmit via droplets and aerosols, or exhaled particles from humans and that proper ventilation helps reduce its transmission by at least 90 percent.

Since equipments are not yet available to measure aerosols, the closest alternative would be measuring the CO2 level in a particular area.  And arise in CO2 level automatically infers a rise in the aerosol level in the air, Lim said.

“Ang aerosol, mao na ang atong ma-exhale, but dili man na mameasure easily. We can measure carbon dioxide much easily,” he added.

COVID-19 Transmission

Based on numerous studies, the transmission rate in enclosed households is at 43.7 percent while closed workplaces is at 26 percent.

In an open workplace, the transmission drops significantly to only 1.4 percent.

Lim said he understands that most of the structures in Cebu City were not designed to have better airflow as the rise in the use of air conditioning over the past 30 years have significantly influenced building design.

Given the situation, the use of CO2 monitors will help structure owners determine if there is a need to introduce adjustments on their ventilation system.

A rise in CO2 level could be risky to building occupants, he said.

The use of a monitor with non-dispersive infrared sensor is considered the most accurate equipment when monitoring CO2 level in a particular area because this gives real-time reading.

CO2 Level

Lim said that a 400 particles per million (ppm) reading is a safe CO2 level for any space no matter how small.

But when the reading increases to 700 to 800 ppm, adjustments will have to be made, like opening of doors and windows, turning on of the ventilation system, switching to the use of electric fans instead of air condition, and reducing the number of people inside a particular space.

If the reading further increases to 800 to 1,000 ppm, this signals the need to adopt structural enhancements that will allow improved airflow.

Lim said that introducing improvements in the room’s ventilation is much safer compared to just limiting the number of occupants at a time.

He said that a well ventilated room that is occupied by 10 people  in a span of four hours has limited risk of infection in comparison with a poorly ventilated space with only 5 occupants.

CO2 Monitor

“We are not endorsing a (particular) brand. There are a lot of brands with NDIS, and the machine is around P2,000 to P3,000 but it will significantly help,” said Lim.

And when installing CO2 monitors, it is important to remember that these should not be placed near windows or doors or even near the room’s ventilation system to avoid “false reading.”

Instead, CO2 monitors should be placed in a strategic place that is at least 0.5 to 2 meters above the ground in order to detect the general CO2 level inside a particular space.

Cebu City’s EOC is now studying the possibility of requiring businesses in the city to adopt the use of CO2 monitors, but they wanted to first consult with establishment owners and managers on the matter. / dcb