I want to commend this article at Wired about an early and widespread misconception about COVID-19 to your attention. Here’s a snippet that contains the meat of the piece:
According to the medical canon, nearly all respiratory infections transmit through coughs or sneezes: Whenever a sick person hacks, bacteria and viruses spray out like bullets from a gun, quickly falling and sticking to any surface within a blast radius of 3 to 6 feet. If these droplets alight on a nose or mouth (or on a hand that then touches the face), they can cause an infection. Only a few diseases were thought to break this droplet rule. Measles and tuberculosis transmit a different way; they’re described as “airborne.†Those pathogens travel inside aerosols, microscopic particles that can stay suspended for hours and travel longer distances. They can spread when contagious people simply breathe.
The distinction between droplet and airborne transmission has enormous consequences. To combat droplets, a leading precaution is to wash hands frequently with soap and water. To fight infectious aerosols, the air itself is the enemy. In hospitals, that means expensive isolation wards and N95 masks for all medical staff.
The books Marr flipped through drew the line between droplets and aerosols at 5 microns. A micron is a unit of measurement equal to one-millionth of a meter. By this definition, any infectious particle smaller than 5 microns in diameter is an aerosol; anything bigger is a droplet. The more she looked, the more she found that number. The WHO and the US Centers for Disease Control and Prevention also listed 5 microns as the fulcrum on which the droplet-aerosol dichotomy toggled.
There was just one literally tiny problem: “The physics of it is all wrong,†Marr says. That much seemed obvious to her from everything she knew about how things move through air. Reality is far messier, with particles much larger than 5 microns staying afloat and behaving like aerosols, depending on heat, humidity, and airspeed. “I’d see the wrong number over and over again, and I just found that disturbing,†she says. The error meant that the medical community had a distorted picture of how people might get sick.
I recommend reading the whole thing. The balance of the article is a detective story. Where did the 5 micron theory originate? It has just about every aspect of a good detective story short of assembling all the suspects in a living room to explain the crime.
It’s also a story about how medical guidance is arrived at. Spoiler: it isn’t necessarily all about the science. And how you go about changing the hive mind of a health care bureaucracy.
I have been involved in a couple of efforts to figure out how long held beliefs were developed and why we held them. Much like this case they all had their basis in some scientific study, but the findings were misused and then carried on as fact until someone looked at them again. It also seems somewhat common, though we didnt see it in our searches, that there is a key figure or group that opposes change for whatever reason and that keeps a wrong idea in place.
In the case of Covid I think that Li’s comment is important.
“SARS-CoV-2, like many respiratory diseases, is airborne, but not wildly so. It isn’t like measles, which is so contagious it infects 90 percent of susceptible people exposed to someone with the virus. And the evidence hasn’t shown that the coronavirus often infects people over long distances. Or in well-ventilated spaces. The virus spreads most effectively in the immediate vicinity of a contagious person, which is to say that most of the time it looks an awful lot like a textbook droplet-based pathogen. ”
The strategies of masking and distancing would still apply. To that we should be adding better ventilation which is a more expensive proposition and will take longer. We need to figure out where it will be cost effective to change ventilation schemes. I doubt it makes much difference in residential settings but maybe it could be effective enough to keep hotels running? Restaurants, stores, offices? What are the chances we can convince businesses to invest in better ventilation now that we have vaccines?
Steve
As I’ve mentioned before by June 2020 the building in which my former employer had offices had installed AirPHX units throughout. They aren’t free but they aren’t that expensive, either. To my eye they look like a reasonable solution.
Not sure if that alone is adequate or if you also need to increase room turnovers also.
Steve
Brings two interesting stores from science.
One is the discovery that ulcers are mostly caused by H. Pylori; which won Barry Marshall a Nobel Prize. In prior decades it was believed stomach ulcers were caused by stress or lifestyle factors, despite evidence of a bacterial cause dating to the 1800’s.
The other is the dual particle/wave nature of light. Physicists were divided for 300 years between the particle theory of light (championed by Newton) and the wave theory of light (championed by Descartes). It wasn’t until the 20th century with Quantum Mechanics that physicists concluded that light was in fact both a particle and a wave, and whether it behaved like a particle or a wave depended on the context of the experiment. In both cases, perhaps the linguistics of two distinct categories made it harder for people to reconcile the continuum nature of the subject matter.
My guess is HVAC improvements will be a gradual process (perhaps mandated by building codes). Presuming the science shows the benefits in reducing disease, the cost benefit should be there for new construction.
“A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it. . . . An important scientific innovation rarely makes its way by gradually winning over and converting its opponents: it rarely happens that Saul becomes Paul. What does happen is that its opponents gradually die out, and that the growing generation is familiarized with the ideas from the beginning: another instance of the fact that the future lies with the youth.
— Max Planck, Scientific autobiography, 1950, p. 33, 97