The world must wake to and listen to scientists warning that SARS-CoV-2 can travel across rooms and between open spaces in buildings. There is no 6 feet rule, and 6 feet doesn’t mean safety! Many will die if this is not made very clear.
A report by Becky Spot published in Medium yesterday said:
Several months into the pandemic, we have been well educated about the 6 feet apart rule to keep social distancing. It’s worth asking, however: “Where did this rule come from?” Critically, it is based on work that was done in the 1930s by William F. Wells, et al., who measured the duration and distance it takes for large droplets to fall to the ground — on the basis of understanding the spread of tuberculosis. In fact, the presumption then was that the droplets were going to dry out and leave a virus exposed to the elements — desiccating within seconds. However, TB has proven to be very air-stable. The distance calculated by the 6-foot rule, also known as the d2 law, can only be applied to an isolated spherical water droplet.
In the decades since, there has been little push to examine or extend these ideas and Wells’ work became the rule of thumb for all medical agencies — including the WHO — in part because of necessity. Compounding all of this is the fact that everyone will go back inside as the winter months approach. We must have a look at the Wells’ assumptions again. In fact, we understand now that when someone coughs, sneezes, and breathes, significant numbers of droplets are smaller than 10 micron. In non-technical terms, that’s about 1/5 the diameter of a human hair, so small the human eye cannot really see them. We also know those droplets can travel up to 17 meters — and beyond — indoors, while any droplets smaller than 5 micron (1/10 the diameter of a human hair, if we are now splitting hairs) do not fall to the ground at all. They will travel in air currents until they are sucked into someone’s lungs, land and remain on a random surface, or find a circulating path through a ventilation system.
As small particles dry out, we must also remember that the relative humidity will also have an effect on how quickly the virus dries out. According to a paper from K.L Cheong, et al(2) recently, the Wells model is not very effective when it comes to the SARS-CoV-2 virus and practically any other similar-sized and respired types of viruses. So, we can discern that SARS-CoV-2 will stay airborne for a prolonged period and will still have an outer layer of saliva (as well as salts, proteins, and other inorganic and organic matter). They will form nuclei and aggregate in numbers, which in itself will likewise alter the evaporation rates(3). Until the airborne viral particles reach HVAC filters, they have the potential to be active and infect those not wearing proper protective masks. This remains an area of active debate, however, as arguments ensue about how infectious these small particles really are.
Ebee ka nke a na-ahapụ anyị?
It is better to remain outside the line of fire of course, so keeping as distanced as possible from other individuals is a must. It should be reinforced that 6 feet is not a guarantee of safety but more likely the least distance as you approach individuals, especially — and in particular — indoors. For the foreseeable future, wearing masks is going to be a necessity.
What about indoors — am I protected by filters?
The answer is, of course, yes na no. If you have HEPA filters, that’s an awesome way to keep air cleaner, but not completely clean from viral loads. But, with standard cloth filters (polymer or cotton), they all have a Minimum Efficiency Reporting Value (MERV) rating which ranges from 1 (least porous) to 20 (most porous) — this is something most people have never come across.
So, yes it’s good to filter the air, but not all filters are capable of stopping the virus. According to ASHRAE, with a MERV 14 filter, it can take 4 or 5 flushes of air — recycling the same air — before air quality improves. Most homes use MERV 4–6 depending on tolerance for pollen, dust, and dander; schools and office areas may use as high as MERV 8; and for the most filtered air outside of HEPA filters, there is MERV 16.
What do we do now — what is really safe?
The debate remains as to why 6 feet apart has become the standard even after 86 years. That’s not saying the studies were bad, they were advanced for their time, like comparing a propeller plane with a space shuttle. Today, we know much more about flow dynamics, viruses, and nanoparticles (even modeling exactly how they work). Feynman first introduced the “idea” of nanotechnology in 1959, 15 years after the 6-foot “rule” was brought into place(4). It would be another 40 years before instruments could readily reveal these viruses.
The world must wake to — and listen to — scientists warning that SARS-CoV-2 can travel across rooms and between open spaces in buildings.
Until we tackle this, we are trying to perform delicate surgery with bolt cutters and a saw.
IHE Ị GA-Ewepụ na edemede a:
- We also know those droplets can travel up to 17 meters — and beyond — indoors, while any droplets smaller than 5 micron (1/10 the diameter of a human hair, if we are now splitting hairs) do not fall to the ground at all.
- In the decades since, there has been little push to examine or extend these ideas and Wells' work became the rule of thumb for all medical agencies — including the WHO — in part because of necessity.
- In fact, the presumption then was that the droplets were going to dry out and leave a virus exposed to the elements — desiccating within seconds.
