Reading this article, and more importantly about the hundreds of scientists who disagree with the WHO’s position on the likely transmission route of Covid, brings me straight to the heart of one of the most basic principles an HVAC engineer needs to grasp – air movement and it’s ability to convey particles along with it. This determines the satisfaction, health, safety and comfort of building occupants as we design air conditioning and ventilation systems for hospitals, schools, offices, and all sorts of public and private spaces (bathrooms among them).
Bottom line: size matters….especially right now when we talk about Covid.
The virus is tiny in size and it makes its way out of infected people through the air we expel. That can be on larger droplets we shoot out forcefully (sneezing, shouting…) or on aerosols (tinier sized moist air particles during less active activities). How long the particles stay in the air is size dependent. How concentrated they stay in the air is related to ventilation and air flow. Your potential risk for breathing them in is time and distance related.
Think of when you spray air freshener or perfume in a room. If the air is still, the tiny aerosol particles, being the same size & density of the air, will float and disperse throughout the whole space. The scent will travel to every corner of the room and linger for awhile. It’s known as diffusion.
On the other hand, if you spritz water from a spray bottle, it shoots out, arcs downward and lands on the nearby surfaces. Those are liquid droplets, much larger in size, and they have a trajectory similar to a ball that’s been thrown across a field.
We emit all different sized particles when we breathe, talk, cough, sneeze, sing and yell, so a virus has lots of particle choices as it hitches a ride out of one person on its search for a new host. So until scientists and health experts can prove all the ways this virus spreads, be mindful.
Some advice from this article: “For now, whether coronavirus is airborne, the guidance remains mostly the same. Avoid crowded indoor locations, or if you must be indoors, try to spend less time there. The virus may accumulate in poorly ventilated spaces, increasing the risk of infection.
You should continue to maintain social distancing measures. When you’re out, put on a mask. Wash your hands. And keep listening to advice from local health authorities with the caveat that information can — and will — change based on new evidence.”