Whether you’ve already returned to your workplace or will do so eventually, it’s a good idea to ask what steps your employer has taken to improve indoor air quality.

The more time we spend indoors with other people, the more likely we are to breathe each other’s exhaled air — and germs. The majority of scientists now agree that the coronavirus is airborne, and infectious droplets can linger in the air, float around the room or build up in spaces with poor air flow, like conference rooms.

Early in the pandemic, a coronavirus outbreak on the 11th floor of an office building in South Korea showed how just one infectious person can increase the risk for everyone in a workplace. Out of 216 people on the floor, 94 were infected. Most of the infected worked in rows of desks grouped on one side of the office.

Even before COVID-19, it was clear that indoor air quality could affect workers’ health. A well-known Harvard study of more than 3,000 workers showed that sick leave increased by 53% among employees in poorly ventilated areas.

While vaccination requirements and masking remain a first line of defense against COVID-19, ventilation improvements in schools and workplaces are essential to stopping the spread of the coronavirus, said Dr. Ashish K. Jha, dean of the Brown University School of Public Health.

“Improving indoor air quality can be a really powerful tool,” Jha said.


In addition to asking questions about ventilation, ask about vaccination policies, staggered workdays to reduce capacity, COVID testing plans, mask requirements and how the building is monitoring outside workers, like delivery people and cleaning crews.

While some of the technical details around air quality can be confusing, you don’t have to be a ventilation expert to figure out what extra precautions your employer has taken. Asking about efforts to improve indoor air quality can help you decide how much time you might spend there, whether to mask up or buy a portable air cleaner, or whether to change your work schedule or work from home, if it’s an option.

Here are six questions you can ask your human resources or facilities office at your workplace. The questions are also useful for evaluating air quality improvements at gyms, in classrooms and in restaurants and other public spaces. Most buildings won’t implement all of these changes, but even one or two of them can make a difference.

What improvements have you made to the ventilation system?

Most newer buildings rely on mechanical heating, ventilation and air conditioning systems, known as HVAC, that use a combination of air filters and outdoor air to dilute and remove viral particles and other pollutants. Buildings can take several steps to improve HVAC performance, including:

Improving their MERV ratings: For starters, facilities can improve what’s known as the MERV rating (MERV stands for Minimum Efficiency Reporting Values). The higher the rating, the better the filter is at trapping specific types of particles.

Before the pandemic, many buildings used MERV 8 filters, which allow for comfort and energy efficiency but aren’t designed for infection control. New industry guidelines advise buildings to upgrade to at least a MERV 13 filter, which traps 85% or more of risky particles. However, not every ventilation system can upgrade to a MERV 13 filter; a MERV 11 filter may be the highest grade filter some systems can handle.


Disabling demand-controlled ventilation: Facilities can also disable demand-controlled ventilation. To save energy, some systems monitor building occupancy based on carbon dioxide levels, which rise when we exhale. When fewer people are present, the system reduces the rate of outdoor air. “It’s a way to stop ventilating the space to save money,” said Richard Corsi, dean of the College of Engineering at University of California, Davis. “But after people leave an area, we need to continue to ventilate so we can purge the space of any aerosol particles left in the air.”

Increasing outdoor air: Some buildings can increase their use of outdoor air. Air quality experts recommend adjusting outdoor air dampers, which are movable plates that can bring in more outside air. This isn’t advised in communities with poor outdoor air quality, such as areas with active wildfires.

Can the windows be opened?

Some older buildings and classrooms may lack modern ventilation systems, but simply opening windows can improve air quality. A recent study of infected college students in an isolation dormitory at the University of Oregon found that opening a window could reduce the amount of coronavirus in a room by half.

While opening a window can help, the effect is greater if you can cross ventilate by opening windows on different sides of the room. Adding box fans to windows and turning on exhaust fans in kitchen and bathroom areas can also improve ventilation in homes and in buildings without modern systems.

What is the air change rate?

Air changes per hour, or ACH, number is the industry term for how often air in a room is replaced by outdoor air. (Cleaning the air with filters can create the equivalent of air change.) While some experts suggest four to six air changes per hour (that’s fresh or clean air every 10 to 15 minutes), many buildings fall short of that standard. It’s recommended that schools have at least three air changes, but many classrooms are closer to one and a half, experts say. Airplanes and newer hospitals may have anywhere from 10 to 20 air changes per hour. Air change rates or their equivalent can be improved by upgrading the overall ventilation system or filters, increasing the amount of outdoor air (by opening windows or ventilation dampers), adding exhaust fans or by adding portable air filters.

While there’s no magic number for air change rates to avoid COVID-19, the higher the better, Corsi said.


Are you using portable air cleaners?

Portable air cleaners equipped with HEPA filters do a surprisingly good job of removing viral particles from the air, but only if the machine used is appropriate for the size of the space. Look for a machine with a clean air delivery rate, of at least 300 cubic feet per minute, and follow manufacturer guidance on how big a space it can clean. You may need more than one machine for a larger space. The Association for Home Appliance Manufacturers has a guide for buying air cleaners.

Adding an air cleaner can partly compensate for a less efficient ventilation system, depending on the size of the room. In some cases, “one of these little portable air cleaners can effectively double the ventilation rate in the classroom,” Corsi said.

A study in a Melbourne, Australia, hospital recently showed that adding two portable air cleaners to a patient’s room eliminated 99% of aerosols in minutes, reportedly raising the protection level to about 30 air changes per hour.

Who is monitoring air quality?

Carbon dioxide sensors can indicate how well a ventilation system is working. Virus scientists and air quality experts sometimes carry portable CO2 detection devices. Linsey Marr of Virginia Tech, one of the world’s leading experts on viral transmission, has used such a device to check levels at her gym and in grocery stores.

“Carbon dioxide is in our exhaled breath,” Marr said. “If the levels get high indoors, it means people’s exhaled breath is building up, and that exhaled breath of course could contain virus if someone is infected.”

If your company isn’t using CO2 monitoring, you can buy your own machine for $100 to $200. In general, you don’t want the CO2 number to rise above 800. In gyms, where people are breathing heavily, Marr advises leaving or masking up if the number goes above 600.


Does the building rely on unproven technologies?

Many companies are installing what the Environmental Protection Agency calls “emerging technologies,” including one called a needlepoint bipolar ionization system. The system claims to use positive and negative particles to help remove viruses from the air. But many of the world’s leading experts on indoor air quality, including Joseph Allen at Harvard and Shelly Miller at the University of Colorado, Boulder, question the effectiveness of the technology. “There’s a reason you haven’t seen a single indoor air quality expert recommend this technology,” tweeted Allen.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), which makes recommendations about indoor air quality standards, has said that bipolar ionization is one of several unproven technologies.

The EPA has said that the devices can create potentially harmful byproducts. “As typical of newer technologies, the evidence for safety and effectiveness is less documented than for more established ones, such as filtration,” the agency wrote on its website. “Bipolar ionization has the potential to generate ozone and other potentially harmful byproducts indoors.”

Despite this skepticism, many workplaces are installing them anyway.

“These companies have done a great job of marketing,” Marr said. “It makes businesses feel like they’ve done something.”