Six steps to slowing airborne aerosol coronavirus transmission |

Six steps to slowing airborne aerosol coronavirus transmission

Aerosol transmission is less likely outdoors than indoors.
Courtesy Photo / Colorado Parks and Wildlife, Dustin Doskocil
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Aerosols – invisibly fine particles that float in the air around us for minutes or hours – appear to be a major player in the transmission of the coronavirus.

But how do you slow the spread of disease if these invisible floating particles are a serious source of infection? The good news is that the old standbys of washing hands, social distancing, and, when you can’t socially distance outside the home, wearing a mask are still critical mainstays. But the rise of aerosols as a transmission vector requires new additions to those pandemic-fighting tools. They involve deliberate steps to clear the air.

First, avoid places where aerosols accumulate or can waft between people at close range. The Japanese came up with the idea of avoiding the “Three Cs” – closed spaces with poor ventilation, crowded spaces, and close-contact settings such as close-range conversations.

The “close-range conversations” part of that third “C” is surprisingly important: talking emits five to 30 times more aerosols than breathing – and singing and shouting emit even more.

Second, wear a mask in indoor or crowded outdoor environments. Studies increasingly point to masks’ effectiveness in stopping large percentages of not only larger droplets, but also aerosols. Research shows that most masks protect both the wearer and others.

Third, do it outside. Few cases of outdoor COVID-19 transmission have been recorded – despite many mass gatherings such as political protests and crowded beaches. If the weather permits, head outside.

Fourth, keep indoor numbers down. Minimize possible short-range (six feet or less) aerosol transmission. Fewer bodies mean fewer aerosols and less work for HVAC (heating, ventilation, and air conditioning) systems and other viral countermeasures.

Fifth, amp up the HVAC. Building ventilation systems vary. Some bring outside air in; some recirculate inside air with outside air; and some rely on open windows for any outside air at all.

Sixth, use portable air cleaners. Choosing a portable air cleaner is no easy task – there are hundreds of options with vastly different pricing and specs. Air cleaners with HEPA filters and nothing else are recommended.

Between opening windows, running HVAC systems, and employing portable air cleaners, shoot for five air exchanges per hour in a given space.

Portable air cleaners – alone or in multiples – capable of refreshing a 625-square-foot room’s air several times an hour can cost hundreds of dollars. It’s possible to construct a homemade option by combining a 20-inch by 20-inch MERV 13 or HEPA filter with a common box fan.

Affix the air cleaner to the intake side of the fan, turn the fan on low (easier on the motor given the extra resistance), and voila – one has an air cleaner capable of scrubbing perhaps 90% of the fine aerosols in the 0.3 micron range, the toughest to capture (aerosols ranging from 0.2 microns to 50 microns are suspected of carrying SARS-CoV-2 viruses, which are themselves 0.12 microns wide – about one six-hundredth the breadth of a human hair). Ninety percent is less than the 99.97% of such particles HEPA filters remove, but as with HEPA-filtered devices, air quality will improve as room air passes through multiple times. Plus, it’ll cost less than $50.

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