4 ms·

It's not standard because you can just use filters. Keep in mind the filters have to be able to filter the dead pathogens anyway (usually same size) or else yo

It's not standard because you can just use filters. Keep in mind the filters have to be able to filter the dead pathogens anyway (usually same size) or else you are breathing them, which isn't great either. Better than live ones for sure, but not great. As for UV, you can add it to either residential or commercial easily (some preschools and schools I've visited added them in the past year). It doesn't make sense to install in every room, as you say. On ozone, see https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-and-coronavirus-covid-19 https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-an... and the section on ozone.

cipheredStones 5y ago
What's the risk from dead pathogens - immune overreaction? It's a screwball idea, but I wonder if there might actually be health benefits to reliably killing pathogens without filtering them out of the air - sort of like low-dose inactivated-agent vaccines for everything you would have actually been exposed to otherwise.
bradknowles 5y ago
UV can kill stuff that gets through the filters. Even HEPA filters go down to objects of a certain size, and some viruses are smaller than that. But UV can kill even those smaller viruses.
- ddxxdd 5y ago
  HEPA filters block particles smaller than it's rated size, and they block those particles more easily than larger particles because of Brownian motion and the physics of electrostatically capturing particles.
  - bradknowles 5y ago
    They can block smaller particles, yes. But it’s non-deterministic. More importantly, they don’t block all or even most of the smaller particles. If they did, then they would be rated for the smaller particles that they are blocking.
    - ddxxdd 5y ago
      N95 filters are rated based on how many 0.3-micron particles they can block. They are rated for that particle size because that particle size is the hardest particle size to block and therefore serves as a proper test of the filter's efficiency. If you look at a graph of the blocking efficiency of an N95 filter vs particle size, that graph is a curvy "V" shape, with the bottom of that "V" being at 0.3 microns.
- DannyBee 5y ago
  This is like theoretically true but mostly useless. There is filtration beyond even HEPA. For example, MERV-20 is 99.9999% efficient at 0.1->0.2um particle sizes. It is 99.99% efficient at particle sizes like 0.01um. The bigger issue is not whether you can get filters to do it, it's whether your system was built for the pressure drop you'd need to do it. IE UV's advantage is that it doesn't really drop pressure (but does require some dwell time), not that you can't filter air well enough.
  - bradknowles 5y ago
    I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the size that HEPA is designed for. Of course you can also get higher filtration rating filters to attach to your whole-house air handling units, and — as you point out — those would have to be sized and designed for that. But the whole house units weren’t what I was talking about.

cipheredStones 5y ago

What's the risk from dead pathogens - immune overreaction? It's a screwball idea, but I wonder if there might actually be health benefits to reliably killing pathogens without filtering them out of the air - sort of like low-dose inactivated-agent vaccines for everything you would have actually been exposed to otherwise.

bradknowles 5y ago

UV can kill stuff that gets through the filters. Even HEPA filters go down to objects of a certain size, and some viruses are smaller than that. But UV can kill even those smaller viruses.

ddxxdd 5y ago
HEPA filters block particles smaller than it's rated size, and they block those particles more easily than larger particles because of Brownian motion and the physics of electrostatically capturing particles.
- bradknowles 5y ago
  They can block smaller particles, yes. But it’s non-deterministic. More importantly, they don’t block all or even most of the smaller particles. If they did, then they would be rated for the smaller particles that they are blocking.
  - ddxxdd 5y ago
    N95 filters are rated based on how many 0.3-micron particles they can block. They are rated for that particle size because that particle size is the hardest particle size to block and therefore serves as a proper test of the filter's efficiency. If you look at a graph of the blocking efficiency of an N95 filter vs particle size, that graph is a curvy "V" shape, with the bottom of that "V" being at 0.3 microns.
DannyBee 5y ago
This is like theoretically true but mostly useless. There is filtration beyond even HEPA. For example, MERV-20 is 99.9999% efficient at 0.1->0.2um particle sizes. It is 99.99% efficient at particle sizes like 0.01um. The bigger issue is not whether you can get filters to do it, it's whether your system was built for the pressure drop you'd need to do it. IE UV's advantage is that it doesn't really drop pressure (but does require some dwell time), not that you can't filter air well enough.
- bradknowles 5y ago
  I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the size that HEPA is designed for. Of course you can also get higher filtration rating filters to attach to your whole-house air handling units, and — as you point out — those would have to be sized and designed for that. But the whole house units weren’t what I was talking about.