SAFE AIR - Facts We Should Know to Avoid Covid Infections Indoors

 by Brian T. Lynch, MSW

SAFE AIR - Fifteen essential facts that everyone should know by now. 

An inexpensive co2 monitor for home or office use.

Fact 1) We remain in a global pandemic. 

Fact 2) The pandemic in the U.S. is expected to result in a spike in the number of new weekly infections over the next few months due to the omicron variant. A soon-to-be-released study of early research found that the omicron variant is twice as infectious as the Delta variant. It isn't known yet if the new variant is as pathogenic or less pathogenic than the Delta variant. 

Fact 3) The primary safety measure for everyone to take right now is to get be fully vaccinated, including getting the booster shot. This isn't happening quickly enough in this country right now, but, even if everyone was triple vaccinated, there will always be breakthrough cases of Covid-19. 

Fact 4) According to the CDC, "The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory fluids carrying the infectious virus," from both breath droplets or breath aerosols. Breath droplets are larger moisture particles that we breathe out. They are pulled down by gravity and most fall out of the air within six feet of a person's breath. Aerosols are tiny moisture particles that remain suspended in the air for minutes to hours depending on how small they are. 

Fact 5) Social distancing and mask-wearing in public indoor settings is a good secondary strategy to avoid getting sick or infecting others. It is the essential strategy for one not fully vaccinated.

Fact 6) Most masks can block out the larger breath droplets exhaled by someone near us who is infected with Covid-19. Social distancing allows most of these larger moisture droplets to drop out of the air before reaching us. 

Fact 7) As we breathe, a concentrated "breath-cloud" of aerosols surrounds a person as it dissipates into the surrounding air. Social distancing helps keep us from this potentially infectious breath cloud." 

Fact 8) Most masks are not very effective in keeping us from breathing in infectious aerosols. Some masks are much more efficient at preventing us from expelling aerosols when we breathe. The amount of aerosols a mask material captures, and the amount of air that leaks around the edges of a mask are two important factors. A tightly fitted N95 mask is the most effective of the commonly available mask choices.

What happens to potentially infectious breath aerosols that mix with the air in a room? 

Fact 9) Inhaling a tiny number of an infectious virus does not necessarily result in an infection. There is a tipping point beyond which the amount of virus inhaled will trigger an infection. That point can be different for different people. 

Fact 10) Breath aerosols being exhaled in a room swirl about until gradually diffusing through the space, or even throughout an entire building in some cases (see CDC article). Airflow patterns influence how aerosols mix within the volume of air in a room or building. Without ventilation and/or filtration, aerosols from people's breath build up in any given space. The smaller the air volume, the quicker aerosol concentrations will increase in a room. The more people in a given room, the quicker the aerosols build up. Whether or not the aerosols are infectious depends on whether or not one or more people in the room are shedding the virus. 

Fact 11) If there is no air exchanger in a building's HVAC system (and most systems don't have air exchangers) or if there are no open windows at the very least, breath-released aerosols from an infected person may build up to levels that can result in the transmission of the virus. In other words, the air itself can become infectious. Only the best, closest-fitting N95 masks can trap these tiny breath-aerosols. HEPA air filters on some HVAC systems or portable HEPA air machines can capture some of these aerosols. 

Fact 12) As infectious aerosol concentrations rise, our exposure time in the room should decrease to prevent infections. These two factors, the amount of virus in the air and the length of time you are exposed to it determine whether or not you inhale enough virus to trigger an infection. These are the basic facts about aerosol transmission of the virus that everyone should know.

How do you know if the air is safe to breathe in a room? Directly measuring concentrations of infected aerosols cannot be done in any practical way; however, there is a way to monitor CO2 levels in a room.

Fact 13) Every time we exhale, we release CO2. If there are no other CO2 sources in the room, the concentration of CO2 is a proxy measure for the concentration of breath-aerosols. According to the CDC, this can be a means of identifying how safe the air is in a room.

Fact 14) While many factors impact aerosol concentration levels, the CDC recommends that CO2 levels should not exceed 900 to 1,000 ppm (parts per million) over the background (or ambient) level.  Ambient co2 levels outdoors generally measure about 420 ppm.  Ambient indoor levels may be higher if, for example, there are gas pilot lights on a gas stove. 

Fact 15) An inexpensive monitor to measure CO2 levels for home or office use costs as little as $85. 

Here is an example of how a co2 monitor can be helpful to assure the air in a room is not unsafe. Suppose that the ambient levels in an unoccupied room are 450 ppm and the room is later occupied by people whose Covid status is unknown. Using the CDC guidelines, co2 levels in that room should not exceed 1,350 to 1,450 ppm. If it does reach those levels steps should be taken to lower the co2 levels. Remediation steps may include: 

• Increasing ventilation in the room. The use of exhaust fans in the bathroom and kitchen may be helpful.  In fact, if you are entertaining in your home or working in an office, it is a good idea to leave exhaust fans running during the entire day. 
• Open windows or doors. 
• Move some people to other rooms.
• If you have a HEPA air filter machine, make sure it is on. 
• If you have a window fan, place it in an unoccupied room and bring in fresh air while exhausting room air out windows in the occupied room. 
• If you have a whole house fan, it is able to exchange a large volume of air with fresh air quickly.

Good luck and stay safe!

For more on aerosol transmission and building HAVC systems from the CDC go to: https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html?fbclid=IwAR1QMm-WV7Z1YeUWy2dfaOc3GL8S8H6H7y7c3dUwqCnrrVJL1V_6YsO363M