IT MAY sound disgusting, yet when you enter a room with little or no ventilation you are essentially eating from everyone’s plate that has been in the room over the last 12 hours. When we speak, laugh, talk, and breath, thousands of very small particles are emitted from our mouths. These particles are very small and can float in the air currents of the room for hours. This was of little consequence until the onset of COVID-19, which is transmitted via small airborne particles and has killed over 4.4 million people in just 20 months.
For context, consider a human hair is 70 microns in diameter. The size of small particles that come from our mouths can be as small as 1 micron. Their small size makes them very light and buoyant, and they float in the air for hours. Each time you enter a room that has poor ventilation or no air filtration, you are inhaling particles in the air emitted by anyone in the room within the past 12 hours, which is about the time necessary for pathogens like COVID-19 to die.
Humans primarily use our eyes to sense cleanliness. If we enter an environment that “looks” dirty, we generally leave as soon as possible. The particles that transmit COVID-19 and many other pathogens are far too small to be seen. They are also major “triggers” for allergy and asthma sufferers. The good news is there are low-cost instruments that can “see” the particles and quantify them using something called a PM 2.5 count. A PM 2.5 counter can measure particles below 2.5 microns that are the most dangerous and at a reasonable cost. The bad news is this is not currently being done.
Although COVID-19 is what we are most concerned about now, the physics of airborne transmission is the same for all pathogens. The list is long and includes chickenpox, mumps, measles, whooping cough, tuberculosis, MERS, SARS, the common cold, and many forms of the seasonal flu. And they all behave in a similar pattern. Humidity has a large impact on transmission rates. In the winter months air is much dryer causing water in small particles to dry out making them lighter and more buoyant. The result is higher amounts of particles in the air, resulting in higher concentrations of pathogens, and therefore higher chances of contracting the virus. This is why it is more common to catch a cold in the winter than in the summer. We are indoors more, and the humidity is lower, a perfect storm for pathogen transmission.
However, there is something we can do about this issue. Improving indoor air ventilation is a preventative measure that is pathogen agnostic. It does not matter whether it’s the delta variant or the Spanish flu, cleaning the indoor air will reduce the risk of transmission. It can be done by two well understood methods; either bring in more outside fresh air, or by filtering the internal air to capture and kill the pathogens. Bringing in outside air in New Hampshire can work for some of the year, but becomes a cost issue in the winter. However, filtering the indoor air can be done anytime, and at reasonable cost.
Indoor air filtration remains the safest, most energy-efficient means of improving human health in indoor spaces; and it is best achieved using portable HEPA filtration devices. HEPA (High Efficiency Particulate Air) filters are the “gold standard” of filtration, able to remove 99.997% of all particles. They have been shown to be effective at mitigating airborne pathogens including influenza for over 20 years and can trap particles as small as .01 microns in size. Both the CDC and the WHO are now recommending portable HEPA filtration devices for indoor spaces.
Today’s heating and cooling systems were designed primarily for thermal comfort, not pathogen mitigation. Even with the best filters that can be installed, a 1-micron pathogen will likely get through a typical central heating or cooling system filter. That’s because the amount of pressure required to push the air through a HEPA filter is too large for general HVAC systems. And for many HVAC systems, little or no outside air is added to the recirculation. This is why portable HEPA filtration is the best solution for our indoor air environments.
When I speak to building owners or managers about indoor air quality, I get a lot of “don’t-worry-about-it” answers. These include: the vaccination will take care of it, we have just installed a new HVAC system, it’s no worse here than anywhere else. These responses are designed to make us feel safe, but science does not support them.
We need to clean our indoor air to defend against future pathogens to make it safe for our students, employees, teachers and customers. There is no need to be eating from a stranger’s plate.