Study finds gaps in evidence for air-cleaning technologies to prevent infections
news.cuanschutz.edu
news.cuanschutz.edu
If we know pathogens cause disease, and we know filtering removes pathogens from the air (and we can test and verify that) we don't need to run a double blind study to verify they work.
It's the same reason you don't need to run a double blind study on whether seat belts work. We understand the cause and effect of car ejections and windshield/steering wheel impacts on human bodies. Seat belts are designed to mitigate these incidents and are tested and validated in the lab using formal science and engineering.
We might need some historical investigation into the road that was travelled to get seatbelts to where they are now (physically, legally, and socially). I'm a millennial and I remember growing up where similar arguments were made:
- "If it's my time to go, then it's God's will"
- "It's uncomfortable"
- zero/inconsistent law enforcement
- "If the car rolls over than it can trap you"
To now, where it's entirely automatic and incredibly wild to even suggest being without a seatbelt.
Seems like some evidence would be helpful.
The article is complaining that every study doesn't redo the evidence collection, end-to-end, every time. That's not realistic and not necessary.
A lot of your specific questions are leading (with a nothing-we-can-do attitude underneath) or asking the wrong question (eg expecting one universal number for "hours of filtration per infection prevented").
For instance the correct answer may be air filters in classrooms and buses and workplaces, but strangely your line of questioning doesn't even consider that possibility.
This would be like someone in the 1800s questioning how handwashing avoids Cholera if they don't wash their hands at home. I think I see a solution to this one...
Actually, seat belts are a weird example. After they were invented, there were more car crashes since people trusted they were protected. Without seat belts people were more cautious. They were a net positive of course, but some different situations/inventions/studies might have effects that are the opposite of what you would expect.
Recent testing on the Vacuum Wars channel showed big differences between filters from the vacuum manufacturer and off-brand "HEPA" filters. Probably the same applies everywhere.
There are standards:
> Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% (ISO, European Standard)[4][5] or 99.97% (ASME, U.S. DOE)[6][7] of particles whose diameter is equal to 0.3 μm, with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.[8]
>Your HEPA filters must be real ones.
HEPA H13 only means the filter was tested to 99.97% particle efficiency at the most difficult particle size. There's nothing magical about this number. In reality air filters can often clean better with an E11 or E12 filter (tested to 95% and 99.5% respectively), because these filters allow much greater airflow from the same fan.[0]
Remember, the clean air is immediately mixing with the dirty room air. If you get twice the airflow while "only" letting 5% of particles through, that's a good tradeoff.
CADR (tested by AHAM, not just the manufacturer's claim!) is what really matters, not HEPA vs non-HEPA.
Naturally, you would have to account what changes in the sample during shipping, due to the short half-life...
Get a professional measurement and compare. This Reddit thread gave me pause [1].
[1] https://www.reddit.com/r/radon/comments/ptz8tt/professional_...
Complete silence, performance beyond anything people are used to at home. Most people don't even know the choice exists, and even if you go to a bougie specialty cooking store they'll try to dissuade you from this and instead sell you on a higher priced product that doesn't work as well.
One annoyance is that almost none of the vent hood stick out far enough, ideally you want the vent hood to stick out a few inches (at least) past the front of the cook top, but almost none of them do that (likely due to head bumping issues, understandable) so a lot of effluent still escapes.
It's one of those ideas that works fine when it's just a rare thing, but if 100% of households had one I guarantee we'd see headlines like "Wasteful Exhaust Vents Burn As Much Energy As Cleveland" etc etc.
I for one welcome our fume hood inspired overlords. The nice thing about fume hoods is that they're optimized for maximum extraction efficiency for a minimum extraction volume.
Everyone notices the side walls, but an overlooked secret of fume hoods is that they extract air backwards toward the back wall, not just upward.
Makeup air just ensures the exhaust meets its rated flow rate. It doesn't reduce heating or cooling costs (if anything it increases them).
Walls and floors always have positive charge conducted from the ground outside relative to the air, no sparks means ozone in too small concentrations to worry about. Dust, smoke, bacteria and viruses stick to walls not the inside of lungs and the air is clean and odorless. You can shine a very bright flashlight through it in a dark room and see absolutely no beam. Every so often you sponge off the walls with strong cleaning solution. Latex paint stains easily near the device which is a subtle way of reminding you how germy it really would have been. Use plastic over walls near the device to save yourself some color matching and painting.
Over all these years, the most annoying thing has been other people trying to sell me HEPA filter solutions with screaming fans that need accessory replacement often. They insist I'm killing myself with ozone as a fear tactic. Few people sell just ionizers or sabotage the concept by selling weak/ineffective ones... because HEPA is big money.
Ionizers use tiny energy and no recurring supplies. Just make sure your electronics are grounded well.
I watched a grand designs episode where the parents (well, inflicted by the wife) Munchausen by proxied these allergies onto their kids. They were obsessive about having an allergy free house and spent hundreds of thousands building one with, basically a lesser version of what you explained up there.
Revisiting several years later, the children had integrated with society (amazing that they weren’t homeschooled) and lo and behold - allergy free.
The provocative host coaxed out of the parents that they believed that the house did bugger all in terms of helping their children.
I wonder how the kids are doing now without their namby mother
Edit: Sorry, you did address that.
> no sparks means ozone in too small concentrations to worry about.
Have you actually measured?
* https://www.youtube.com/watch?v=vt0GLbi20Q4
* https://indoorchem.org/publications/
Playlist of the various presentations from the conference:
* https://www.youtube.com/watch?v=J2iHOCI2hz4&list=PLsc2-5fAgM...
Generally: avoid any use of electronics to 'do stuff' to the air or pathogens (e.g. UV) and just use high-MERV / HEPA filters, and use an ERV to vent stale air and bring in (filtered, conditioned) outside air.
Smoke can be dealt with via a carbon filter and you don't have to do a chemistry experiment in your house.
> Upgrading to a filter rated MERV 13 or higher can be especially important during smoky periods to effectively remove fine particle pollution from smoke in the indoor air.
* https://www.epa.gov/wildfire-smoke-course/preparing-fire-sea...
The carbon is for the smell. The EPA also points to this California list, which include "mechanical" types which do not use electronic measures:
* https://ww2.arb.ca.gov/list-carb-certified-air-cleaning-devi...
The main challenge is the resistance to airflow (US: inches w.c.) that can be a problem with for HVAC equipment, which is why you want a large surface area, e.g.:
* https://electronicaircleaners.com/docs/aprilaire_2416_2216_a...
* https://www.aprilaire.com/whole-house-products/air-purifiers...
Many HVAC people will recommend thicker filters (3-6" thick) if using a higher MERV, but the 1" 3M 1900 often has more actual surface area if laid flat.
Testing by Project Farm and others showed the 3M 1900 filter has the lowest airflow resistance of any 1" high-MERV filter. If your HVAC only accepts a 1" filter, that's the only brand I'd use. Change the filter ideally every 3 months, but to avoid costly HVAC repairs don't exceed 6 months maximum.
It's important to follow the manufacturers recommendations for the total pressure drop including the filter (this can be measured with a $10 radon manometer), but if the manufacture says something silly like "avoid high MERV filters" then you can safely ignore that claim provided you abide by the maximum pressure drop specced.
This is just an issue with residential HVAC, but of course the residential side has always been messed up...
https://static1.squarespace.com/static/6320b844c3820725e4d56...
Outside air needs to be filtered otherwise you can bring in pollen and other things (e.g., exhaust/brake dust from cars if near heavy arteries). Avoid UV for residences:
A lot of stuff sold as HEPA doesn’t meet the original HEPA standards though, so needs to be actually rated for the super small particles.
Even basic airflow understanding is surprisingly not common knowledge. IE for air to leave a room occupied by humans, then air needs a path into that room too.
I commonly see ceiling exhaust fans in bathroom showers and toilets with windows sealed shut. The door is meant to be closed... so the only gap for air to come into the room is around the door somehow - while the exhaust fan struggles.
I even visited one host who implemented a seal along the bottom of the door because:
1. Shower creates steam and with the above mentioned little airflow, that steam stayed around.
2. So the exhaust fan had to run while they dried themselves with a towel.
3. But they didn't like getting cold feet from the draft of air coming in under the door...
I could not convince them they needed an air intake vent. :-(
Similar but different, a couple of times now I've been in hotel rooms with a bar fridge buzzing away entirely enclosed in a cupboard. Extrapolate that to the hundred rooms or more of the hotel and it is a colossal waste thanks to a "simple" understanding of airflow.
If the building has central air heating or cooling, having a vent into the bathroom is standard. That’s more than enough for the exhaust fan to pull from.
In areas where central air is uncommon, you need a decent door undercut. A surprising amount of air can flow around a door and modern exhaust fans can pull a relatively good vacuum.
I live in an apartment above a busy road, and my building has no central HVAC. Opening my windows makes the air (much, much) worse.
It took a while to figure this out, so from the ~1.5 years I've lived here, I've accumulated huge, thick coats of brake dust on my windowsills, in my carpets, on the blades of my air-circulation floor... and so on. Probably am half-way to developing COPD.
I do still "replenish air from outside", though! ...through a three-stage filter. (I put an industrial air scrubber on my balcony, and fed the exhaust from it inside through the same kind of doorjam seal you'd use for a portable AC unit.)
I still get noxious fumes coming in sometimes, though. I had to set the thing up on a timer so it wouldn't pull air in during rush hour.
The only remaining aspect is how well do they clear air that is constantly getting dirty that has been tested as well, for the most part 6 air changes an hour seems to drastically reduce the particle count.
The problem with medical research "questions" on filtration currently is it thinks random control trials are the gold standard of proof. They aren't physics and engineering tests are a much higher quality of science and evidence. Filters work, respirators do work to remove viruses because we know the size of aerosol they tend to live in (1-5 microns mostly for something like Covid) and how effective the filters are at those particle sizes.
I don't really know if they help to prevent infections but my wife has Long Covid and every time there is too much dust, pollen or smoke around us she gets pretty bad.
So we decided to buy them with little proof after she noticed she feels somewhat better when staying in a room with one. It could even be partially placebo but for the days with too much particles from outside I think it really helps.
Maybe we should rather have a full control of air flows in our home but that would be a huge investment for a very old house, also having air flowing with windows partially open on dry days also seems to help. Humidity ( and certainly mold) also has a clear negative effect so I had to buy a dehumidifier too
The problem is that such low-porosity filters struggle to even let air move through them. And if you don't move a lot of air, you aren't cleaning a lot of air. At low fan speeds they're effectively placebo for how little they do.
You can get around this by adding yet more powerful fans and cranking up their speed, but then it sounds like a jet engine. Everyone just ends up turning them off (or way down) because they're too noisy - defeating the purpose.
If you just want non-virus stuff (pollen, smoke, dust) then don't go HEPA. Go with something like MERV-13. They come in standard off the shelf furnace style filters. They're way cheaper than HEPA and way better for most use cases.
HEPA only makes sense for something as fine as viruses, or if you only get a single pass to do the filtering. For anything that circulates (like in a house) it makes 0 sense.
Yes that's technically true, but this is just a grant money grab.
It's not a serious attempt to study these things.
Really feels like they went so meta here they lost the plot.
Complaints about fails to catch covid. People are buying air filters to fish out particulate matter not fix a 2022 pandemic.
To say they failed to see the forest for all the trees would be a kindness
If you want to sustain this claim, show us the process by which someone's career was truncated by researching air filtration.
You're clearly pushing an agenda. The problem is that these kind of filtration systems couldn't be rolled out en-masse across the world.
During COVID hospitals absolutely were using air filtration systems and places where it made sense (I remember COVID doctor's conferences had advanced filters for each room).
> Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source
2022: https://pubmed.ncbi.nlm.nih.gov/35947419/
2022: https://pubmed.ncbi.nlm.nih.gov/34098798/
2021: https://www.cdc.gov/mmwr/volumes/70/wr/mm7027e1.htmThis was also interesting:
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
Masks and HEPA filters can block droplets that contain viruses. Neither filters out actual virus particles.
The article’s point is we haven’t precisely studied what those probabilities are.
https://www.today.com/health/dr-fauci-shows-how-wear-2-masks...
More recently, on NPR’s The Pulse was this:
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
Let’s just say “the science” we were fed during COVID was lacking in a number of ways.
Please note: The above our not my opinion. These are real things that happened. Please don’t down vote simple because you can’t come to terms with your cognitive dissonance.
https://dynomight.net/ikea-purifier/
Also, I'm pretty sure respiratory viruses need aerosol droplets to get anywhere they can harm you, and those droplets are much bigger than viruses anyway.
The initial theory was that environments like extreme hot and humid climates made it impossible for aerosol droplets to harm people, while dry air increased the risk. This recommendation was change later into the pandemic as new evidence was gathered.
There are similar studies on influenza. There doesn't seem a strong consensus on what environments are safe, or how long such viruses can last outside of large droplets. There is a lot of factors in play, including the virus itself.
> Early in the pandemic, his efforts focused on lowering inhalation dose of virus-laden aerosol particles indoors. He led an effort to develop an educational tool for assessing parallel interventions for lowering inhalation dose for aerosols and risk of infection in buildings. His concept of a low-cost and effective do-it-yourself air cleaner to combat virus-laden aerosol particles and wildfire smoke has become known worldwide as the Corsi-Rosenthal Box. He recently chaired a National Academies committee responsible for the 2024 report, “Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions.”
An awful lot of people who pay attention to engineering solutions for airborne risk reduction - the people who know what ASHRAE is - were saying exactly the same thing throughout nearly the entirety of the pandemic. Because of their advocacy and data, as one example, we got HEPA filters installed in our kids' elementary and preschools as part of the strategy to resume in-person education.
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
Let just say, if you’re looking for baloney, this podcast (and the author / book it discusses) delivers. In short, we were gravely (?) misled.
No I don't. What I remember is that they said a lot about social distancing and going outside, and for those who do have to be around others, they initially said you gotta wear N95 since ordinary masks aren't very effective, then they said there's a shortage of N95 masks so please just wear normal masks since at least it's better than nothing, and save the N95s for the hospitals and other high-risk settings/workers.
If you remember it differently, please explain what I'm misremembering, because (unlike a sizable fraction of the population) I don't remember hearing anything nonsensical or misleading about masks, especially given the information and resources they had available at the time.
What does that have to do with masks?
And wasn't this in the beginning of the lockdown while they were scrambling to figure things out?
And "misleading" in what way? I know you and the rest of HN knew exactly the right thing to do in the very start of lockdown, so it's sad that they never came on HN for advice, but what makes you think they knew a better solution and yet held it from you?
Every jurisdiction had an overreaction fetish. Masks, social distancing and vaccine cards on the left. Ivermectin, detergent pods and intentional exposure on the right.
Maybe there was one with an anti-air filter message. But between New York, the Bay Area, Arizona, Tennessee, Wyoming, London, Frankfurt and New Delhi, I didn’t see it.