In the era of coronavirus, many precautions are being taken to reduce the movement of the virus from human to human. This is a policy based on the statistical science of "flattening the line," to use a phrase that Dr. Anthony Fauci of the President's Coronavirus Task Force has made famous.

This simply means to slow the rate of the spread of the contagion by limiting social contact, including staying in the house. This makes perfect sense if one lives in a single family home which is set apart from other homes, and walls more or less keep heated or cooled air trapped in that house.



But has anyone asked the question, what of high-density apartment buildings, almost all of which rely on central air conditioning and ventilation systems to recirculate air throughout the building? Only hospital and scientific clean rooms provide room-sealing and technology to prevent air from circulating from one room into another. In most modern and not-so-modern high-density, multi-family structures, some level of air circulation from both inside and outside air is part of the plan.

This means some air moves between apartment units, along with whatever is in that air.



If your apartment building is constructed with mechanically forced air ventilation, some of the air blowing in from your apartment's vents comes from other apartments. Air is mechanically forced through corridors and apartments by means of building-wide ductwork.

Apartment air ductwork

Some very modern, and usually expensive, apartment and condominium buildings have localized heat and air conditioning, and a relatively tight seals - still not medical grade - between units. But the vast a majority of apartment buildings in America of any height share air to some extent.

One problem that this causes has come to be known as SBS, "sick building syndrome," a worldwide problem recognized by WHO, the World Health Organization. This is when people in a building suffer from symptoms of illness or become infected with chronic disease from the building they work in or reside in.

One factor cited by WHO in a paper on sick building syndrome is ventilation systems, which means that irritants or pathogens are traveling within the building and giving residents similar symptoms.



In it's description of sick building syndrome the US Environmental Protection Agency explains:

"Most indoor air pollution comes from sources inside the building. For example, adhesives, carpeting, upholstery, manufactured wood products, copy machines, pesticides, and cleaning agents may emit volatile organic compounds (VOCs), including formaldehyde. Environmental tobacco smoke contributes high levels of VOCs, other toxic compounds, and respirable particulate matter."

The last phrase, respirable particulate matter, would include airborne viruses.

One of the most famous instances of building-wide, airborne sickness by pathogen moving through a building's air circulation system was the "Legionnaire's Disease" outbreak in Philadelphia in 1976. In it, 182 mostly men attending an American Legion convention contracted the novel, bacteria-caused disease, and 29 died.



According to RDH Building Science, an international building industry firm started in 1997 that "integrates building physics with the art of design and the practical challenges of construction," most medium and high-rise office and apartment buildings in North America rely on a pressurized corridor system, where a rooftop unit pumps air down into the corridors. That air is then circulated into apartment of office units.



RDH Building Science tweets:

"Though the pressurized corridor system is pervasive throughout North America, there is considerable evidence that this ventilation design does not perform as intended, resulting in poor indoor air quality and occupant comfort complaints."

The business of air conditioning and circulation throughout apartment buildings of any size is called the heating, ventilation, and air conditioning business, or HVAC. In "The Basics of Air Flow" at ACHRnews.com, a leading HVAC industry newsletter, the primer explains:

"When supply air is delivered into a room, an equal amount of air must be removed from the room. This return air (RA) is transported back to the central air system for reprocessing...a percentage of the return air can be reused."

"A percentage of the return air" that can be "reused" refers to the air that has already been circulated through other units. Combined with the intake and mix of outside air, it may not be much, but enough for pathogens to travel in.



As described in an HVAC industry technical paper "Air Flow Distribution in a High-Rise Residential Building," a typical ventilation airflow configuration in a building built in 1974 may consist of the following:

"The building has a mechanical ventilation system, with kitchen and bathroom exhaust fans in each apartment vented into separate vertical shafts which have additional exhaust fans located on the roof. The supply air system for the building is provided by a fan and heating unit on the roof that connects to a vertical shaft which has supply registers in the main hallway on each of the floors. Supply air enters the apartments by a slot under the front door of each unit."

Air quality issues for apartment dwellers is nothing new. From another perspective, an apartment rental industry website writes in "Are You Breathing Healthful Air?"

"Most of us don’t think about the quality of the air we breathe at all — until we begin to suspect that the air in our apartments might be making us sick. As we learn more about how air quality affects common diseases like asthma and with new concerns about “sick building syndrome” in office complexes, more and more people are starting to take air quality seriously."

And coming from yet another viewpoint, an air testing technology firm's website warns:

"Another hazard of apartment living is secondhand smoke. While you may not smoke or allow others to smoke in your individual unit, secondhand smoke from neighboring units may make its way through the ventilation system into your apartment or through cracks in walls, joints, and ceilings."

Indeed, it is interesting that the metropolitan area so far hardest hit by COVID-19 is New York-New Jersey, with the highest population density in the US, meaning high-rise apartments, at about 54,000 people per square mile. Greater Los Angeles, the city, has about 24,000 people per square mile, with all other metropolitan areas trailing fairly far behind.



The NYC - New Jersey metropolitan area is one of the most densely stacked labyrinth of apartments and offices in the world, housing millions of souls mostly vertically all sharing elevators, subways, drinking fountains, door handles, and doorknobs.



As apartment dwellers are asked to stay inside if possible, more research should be done on whether or not open air circulating freely between people, outside, more than six feet apart, might not actually be more healthful than 24/7 confinement in buildings recirculating air, partly from other apartments.

There is much to learn about coronavirus. There is also much to learn about our response to it.





Overview of air movement between apartments in high-rise multi-family dwelling

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