3 ms·

I'm also a little suspicious of relying entirely on the CADR metric. If you're running a filter in an environment that's constantly producing particulates and y

I'm also a little suspicious of relying entirely on the CADR metric. If you're running a filter in an environment that's constantly producing particulates and you need to filter large volumes of air, it seems useful. If you're about to walk into a smoke filled room and have 25 minutes to clean the air first, there's no question that CADR is king. I think it would be interesting to run a purifier in a normal house for 48 hours and see what the steady state particulate levels settle at around the house. I would guess that over a certain threshold CADR, there might not be that much difference. Room air circulation combined with a good enough CADR might even be more important, which is what Dyson claims. For all the people in the bay area worried about the next fire season, CADR is probably the most important since there's an extreme source of particulates. I'm just not sure that's the final say on air purifier effectiveness in less extreme conditions.

bluGill 6y ago
I'm more worried about the random friend who drops by. Sure we wear a mask, but when can we take it off when they are gone?
- Bakary 6y ago
  You have to make sure the filter is HEPA, and calculate whether the device has had the time to do a full air change given the room size and its CADR rating. Viruses are generally too small for even the best filters, but the droplets that carry them are well within what a HEPA filter can manage.
  - Maursault 6y ago
    > Viruses are generally too small for even the best filters... The average diameter of coronavirus particles is around 0.12 μm. The diameter of the envelope is 0.08 μm and the spikes are 0.02 μm long. A P100 HEPA filter will remove as much as 99.97% (for P95 it is 95%) of all airborne particulates with an aerodynamic diameter of 0.3 μm, and particles both larger and smaller are removed with an efficiency greater than 99.97%. Even if viruses are smaller than 0.3 μm, they are an easy target for HEPA filters.
- t-writescode 6y ago
  I’m not a doctor, but isn’t this a lost cause? The masks we all wear are primarily droplet guards, not air filters, they catch splatter that might float. All of the air that blasts out the back and escapes is barely going to be diverted by another mask after it’s already escaped the other mask and has had time to exist, right? I guess for my threat analysis, if you’ve already invited them inside your house and they’ve stayed long enough that you think their breath particulates are floating in the air, you’ve already lost the war, so to speak. Probably just a few minutes will be all that matters, I suspect. If you like, go take a walk and wait for the droplets to land?
  - glenneroo 6y ago
    > I guess for my threat analysis, if you’ve already invited them inside your house and they’ve stayed long enough that you think their breath particulates are floating in the air, you’ve already lost the war, so to speak. That's why ventilation is important if you are sharing a room with other "external" people.
ahaucnx 6y ago
I am also living in an area with high periodic air pollution from wildfires. I have now removed all my stand-alone air purifiers and replaced them with a positive pressure system that works so much better. I wrote about the benefits of that system on our blog: https://www.airgradient.com/blog/2020/01/08/positive-pressure-systems-for-clean-air/ https://www.airgradient.com/blog/2020/01/08/positive-pressur...

bluGill 6y ago

I'm more worried about the random friend who drops by. Sure we wear a mask, but when can we take it off when they are gone?

Bakary 6y ago
You have to make sure the filter is HEPA, and calculate whether the device has had the time to do a full air change given the room size and its CADR rating. Viruses are generally too small for even the best filters, but the droplets that carry them are well within what a HEPA filter can manage.
- Maursault 6y ago
  > Viruses are generally too small for even the best filters... The average diameter of coronavirus particles is around 0.12 μm. The diameter of the envelope is 0.08 μm and the spikes are 0.02 μm long. A P100 HEPA filter will remove as much as 99.97% (for P95 it is 95%) of all airborne particulates with an aerodynamic diameter of 0.3 μm, and particles both larger and smaller are removed with an efficiency greater than 99.97%. Even if viruses are smaller than 0.3 μm, they are an easy target for HEPA filters.
t-writescode 6y ago
I’m not a doctor, but isn’t this a lost cause? The masks we all wear are primarily droplet guards, not air filters, they catch splatter that might float. All of the air that blasts out the back and escapes is barely going to be diverted by another mask after it’s already escaped the other mask and has had time to exist, right? I guess for my threat analysis, if you’ve already invited them inside your house and they’ve stayed long enough that you think their breath particulates are floating in the air, you’ve already lost the war, so to speak. Probably just a few minutes will be all that matters, I suspect. If you like, go take a walk and wait for the droplets to land?
- glenneroo 6y ago
  > I guess for my threat analysis, if you’ve already invited them inside your house and they’ve stayed long enough that you think their breath particulates are floating in the air, you’ve already lost the war, so to speak. That's why ventilation is important if you are sharing a room with other "external" people.

ahaucnx 6y ago

I am also living in an area with high periodic air pollution from wildfires. I have now removed all my stand-alone air purifiers and replaced them with a positive pressure system that works so much better. I wrote about the benefits of that system on our blog: https://www.airgradient.com/blog/2020/01/08/positive-pressure-systems-for-clean-air/ https://www.airgradient.com/blog/2020/01/08/positive-pressur...