We know now that airborne small particles are emitted whenever we breathe, speak, etc. We don’t have much data about how much, if any, Covid viruses are included in the airborne particles. There are many factors: outside vs. inside, crowded small rooms, etc. We know that measles can travel through the air (distances vary) and particles can remain in the air for several hours or longer.
Studies regularly cited are observational (for example, choir practice in a small room and many were infected) or airflow patterns in research labs. Fluid dynamic studies spraying particles to see how far they go. But there is no information about how far viruses can travel in the air. An air sampling study published in late July in hospitals found that Covid was in the air particles in nearby rooms. In hospitals, Covid travels through the air, but the people are very sick and exhaling a lot of air.
The WHO’s original three-foot guideline followed some of the earliest research into how diseases spread. In the 1930s, Harvard researcher William F. Wells measured how far large exhaled droplets traveled and arrived at the three-feet figure. Click the Continue reading link below for more information on the new research study and an excellent Risk Table.
In 2003, a group of researchers found that SARS, an illness caused by a similar coronavirus, was transmitted to others as far as six feet away from an infected person while traveling on an airplane. Several experts have cited this study as the most likely source for the CDC’s six-foot guideline.
A new study analyzes many other studies, published on August 25 in The BMJ (formerly called The British Medical Journal). The study has an extensive analysis (with references) of many research studies on this topic. The article is very detailed but worth reading. To read The BMJ research paper Click Here
My comments: The BMJ research paper uses many studies in analyzing this issue. It is the first time I have seen a very good table of risk factors. Read the paper for lots of information plus extensive references.
I first wrote about this in February 2020 in my appraiser publications to help appraisers. They go inside homes, which is very risky.
“The table above presents a guide to how transmission risk may vary with setting, occupancy level, contact time, and whether face coverings are worn. These estimates apply when everyone is asymptomatic. In the highest risk situations (indoor environments with poor ventilation, high levels of occupancy, prolonged contact time, and no face coverings, such as a crowded bar or night club) physical distancing beyond 2 m (6 ft.) and minimizing occupancy time should be considered. Less stringent distancing is likely to be adequate in low-risk scenarios. People with symptoms (who should, in any case, be self-isolating) tend to have high viral load and more frequent violent respiratory exhalations.”