Ventilation

(an unfinished sketch)

According to José-Luis Jimenez, it has been clear since the start of the COVID 19 pandemic—since the March 10, 2020, Skagit Valley choir incident [1]—that this disease is spread by aerosols, or small airborne particles. It is not so much spread by larger droplets, or touch, or contact with surfaces that have been touched. It is spread by air.

The Skagit Valley Choral knew there was COVID (as yet unnamed, but known to be a novel respiratory virus) in the community, so they set up their rehearsal very carefully and thoughtfully in a gymnasium with social distancing. It was documented where everyone was positioned, for how long, and in what size of room. They were singing, so everyone was exhaling large amounts of air into the room. After the rehearsal, 53 of the 61 people attending got sick with COVID 19 symptoms and 2 people died. Tragic.

Since the amount of time, volume of the room, and location of individuals was known, they could model how the virus spread. According to Jimenez, the easiest fit was airborne transmission.

It has taken the public health community a long time to come around to this view. Plexiglass screens were put up and social distancing was recommended to protect from droplets. Surfaces were sanitized to protect from touch. Masking—a way to filter the air—was late to come in to the recommendations. At first, good masks were not available. By the time effective masks were widely available, many mask mandates were coming to an end.

Ventilation has never been highlighted by the public health authorities as a key factor in the spread of COVID 19, even though it is known to be a key factor in airborne transmission and appears to be the primary method of COVID 19 spread. The resistance to embracing the evidence that COVID 19 is transmitted via the air has a long history. After the germ theory of disease transmission came to the forefront, public health officials worked hard to downplay the previous belief that disease was spread by ‘bad air.’ For example, the disease ‘malaria’ was thought to be spread by bad air. Instead, with knowledge of germ transmission, public health messaging promoted washing hands and covering your cough, but not ‘good air.’ This ‘anti-air’ focus persisted into the 2020s.

As Jimenez says, to protect yourself against transmission of aerosol-borne disease, first, protect yourself with ventilation. If ventilation is not an option, use filtration such as MERV-13 filters or N95 masks.

This is a simple protocol to follow but very different from social distancing, washing your hands, or covering your cough.

The ventilation of a space with people in it can be assessed relatively simply by measuring carbon dioxide (CO2) levels. People exhale CO2, so the amount of CO2 in a space is a proxy for how much of the air you are breathing in was expelled by other humans. If it is your own expelled air, there is little concern, but if the expelled air comes from a large number of other people, and this air is not filtered by masks or air filters, then your risk of inhaling and contracting COVID 19 increases.

Baseline CO2 levels from outside air are about 420 parts per million (ppm). A high CO2 level in a space means there is more exhaled air than fresh air.

Some countries, such as Sweden and South Korea, have long seen clean air, or good ventilation, as a health priority. Those countries have fared relatively well in the pandemic. Some countries, like South Korea and Japan have CO2 monitors posted in restaurants and movie theaters. Patrons can see at a glance how good the ventilation is.

One interesting piece of history I recently learned was about the required French lunch break. In France, you are required to leave the building and go out and have lunch. You are not allowed to eat lunch at your desk. Usually this is seen as part of the French culture of a hot lunch as a sort of human right. If you do not have a leisurely, sit-down, hot lunch, you are somewhat uncivilized. Bag lunches, or “brown bags” are not much tolerated.

It turns out that the reason a lunch break is required is not because of some cultural culinary tradition, but because of ventilation! It was so that factory workers would leave the building and it could be aired out. The French lunch break was for health.

Clean air and health are still very much connected and ventilation in buildings in the US is highly variable. Some children attend schools with good ventilation while others do not.

Good ventilation is something worth paying attention to and worth fighting for.

[1] Miller SL, Nazaroff WW, Jimenez JL, Boerstra A, Buonanno G, Dancer SJ, et al. (March 2021). "Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event". Indoor Air. 31 (2): 314–323. Bibcode:2021InAir..31..314M. doi:10.1111/ina.12751. PMC 7537089. PMID 32979298.