Per Wayback machine as of 5/23/25 this webpage still had iffy statements like "may provide a less-snug fit than respirators with head straps such as N95s." web.archive.org/web/20250523...

FINALLY, California public health🥑 got it right ✅. Now they show N95 as clearly superior b/c it has head-straps versus KN95/KF94, "They provide less protection than N95s because they have ear loops."
www.cdph.ca.gov/Programs/CID...

FULL DETAILS come to our presentation at #AAAR2025 in Buffalo, NY at 2:30pm on Wednesday, October 15, 2025

aaarabstracts.com/2025/view_ab...

CONCLUSION: The 3 filters in middle school retained filtration efficiencies like MERV 15 or higher, while 2 filters in the elementary school degraded to MERV 12 or lower => replace annually for school use (home use maybe more often). Anecdotally newer filters lasting longer.

MIDDLE SCHOOL (test #2): Filtration efficiencies were retained (>85%), in the same size range, for filters deployed in the middle school over the four-month period.

MIDDLE SCHOOL (test #1): filters from the middle school (4 months of use) yielded CADRs ranging from 190–213 cfm.

ELEMENTARY SCHOOL (test #2): The filtration efficiencies of the filters deployed in the elementary school degraded to <50% for particles in the 0.3 – 0.4 μm size range, which includes the most penetrating particle size (0.3 μm), over the 16-month period.

ELEMENTARY SCHOOL (test #1): Filters from the elementary school (16-months of use) yielded CADRs between 109–145 cubic feet per minute (cfm)

TEST #2: The size-dependent filtration efficiencies, for particles between 0.3 to 10 µm in diameter, were evaluated per an initial ASHRAE 52.2 test for each filter.

TEST #1: Each filter was tested in a SAFE DIY air cleaner, a 20” box fan paired with a fan shroud and safety screen. The clean air delivery rate (CADR) for particles between 0.3–2.685 µm was evaluated using aerosolized sodium chloride (NaCl) particles operating on low fan speed.

BACKGROUND: Supplementary Air Filtered Exchanges (SAFE) is a peer-reviewed Do-It-Yourself (DIY) air filtration system used in at least 4 San Francisco schools and several households thanks to @SaferTogetherSF @ValerieJay16 @anthrop_inst @crosscutanne.bsky.social
patientknowhow.com/safe.html

HOW LONG DO MERV 16 FILTERS LAST 🏃🏃‍♀️🏃‍♂️?

CDC researcher Christopher Barnes and I decided to find out:

2 DIY SAFE boxes in elementary school 🏫 (16 months)

vs

3 DIY SAFE boxes (4 months) in middle school 🏫

All used daily (per teacher reports).

Ultraviolet radiation vs air filtration to mitigate virus laden aerosol in an occupied clinical room Mitigation measures against infectious aerosols are desperately needed. We aimed to: 1) compare germicidal ultraviolet radiation (GUV) at 254 nm (254-…

J Haz Mat (April 5, 2025): "Our study is the first to directly compare the relative effectiveness of GUV devices (upper-room 254 nm and whole-room 222 nm) and HEPA filters to remove/inactivate model virus laden aerosol in an occupied clinical room."

@crosscutanne.bsky.social

S.F. schools plan to spend $2.9 million on air purifiers to combat wildfire smoke, coronavirus risk The San Francisco Unified School District on Monday announced a plan to spend $2.9...

WHAT’s NEXT in 2026:

In Fall 2021, SFUSD installed “black box” HEPA purifier in 3000+ classrooms. Filter lasts 5 years (~$400). Needs replacement in 2026 @ 2.5 ACH.

For < $400 we get 3 DIY purifiers @ 6+ ACH.

What should SFUSD do in 2026?

www.sfchronicle.com/sf/article/S...

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TEST PROCEDURE (6/5/2025):
1. Open windows to equalize aerosol concentration with outside
2. Close windows
3. Turn on air purifiers under test
4. Track aerosol concentration at 0.3 um every minute

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DETAILS:
Classroom on 2nd floor of SF middle school
6600 cubic feet
Height 11' x Length 24' x Width 25'
No HVAC/ventilation system but it has 4 windows

(2/4)

2 YEARS UPDATE on DIY: This week I tested 10 DIY purifiers in 4 classrooms (160 in use). Still working great!! ✅

CDC & CDPH say we need 5+ air changes per hour (ACH). 🌪️

When I tested $1000+ district-supplied HEPA only 2.5 ACH (sp 2) vs 6.3 ACH for $400 DIY (sp 1) 👀

(1/4)

The role of masks and respirators in preventing respiratory infections in healthcare and community settings The covid-19 pandemic saw frequent changes and conflicts in mask policies and politicization of masks. On reviewing the evidence, including studies published after the pandemic, the data suggest respi...

New review in BMJ by @trishgreenhalgh.bsky.social says for respiratory protection from viruses/bacteria in air:

N95 > surgical > cloth masks > nothing

❗️but only if continuously worn not intermittently. (e.g. taken off for discomfort/eating) www.bmj.com/content/388/...

Good question. What about same daily dose half in AM and half before bed? Blood pressure generally rises at wake up.

According to Quinn, “apart from an elevated risk of venous thromboembolism within 1 year..” “many of the post-acute consequences of COVID-19 may be related to the severity of infectious illness necessitating hospitalization rather than being the direct consequence of infection with SARS-CoV-2.”

Pay attention to *all* variables. If you get in trouble but your cell phone has no service -- you're still in trouble. If you have cell service but EMS is 1 hour away -- you're still in trouble.

Interesting. Is main message here to stay in the green and avoid red by hydrating?

In hot climates, I found my thirst alone is an insufficient signal to hydrate so a conscious hydration strategy is needed to survive extremes. Sometimes electrolyte-drinks are also needed to recover from heat.

Starting to heat up. Share this informative infographic I created for heat waves. There are many variables to consider. Stay safe!

“SARS-CoV-2 airborne detection within different departments of a COVID-19 hospital building and evaluation of air cleaners in air viral load reduction” The pandemic of COVID-19 has brought in light the necessity for the development of novel detection methods for airborne transmitted pathogens, and the…

From COVID-19 hospital wards in Greece:

• "Air viral load in COVID clinic ranged from 25,9 to 1123,7 copies/m3."

• "Air cleaner showed an effective reduction of air viral load, reaching 98.1%."

www.sciencedirect.com/science/arti...

Dean Richard Corsi, with grey hair, mustache, glasses, pink shirt below fleece jacket poses with a blue and gold DIY air cleaner labeled with UC Davis bumper stickers.

1/ The CR Box behind me has been operating for well over 3,000 total hours over the past year (avg about 65 hours per week). It's definitely not looking shiny new. Nonetheless, I just did triplicate measurements of ultrafine particle (UFP) concentrations outside and inside the box ..... more

This WHO video seems to attribute particulate air pollution to smokestacks and vehicles but as we are finding out, are wildfires, land fires, and burning of vegetation a more significant source of particulate pollution globally? www.nature.com/articles/s41...

Refreshing message from WHO

These DIY air purifiers could make clean air more accessible during wildfires Homemade air purifiers can filter air faster, making them an affordable alternative to more expensive commercial products.

Thanks to Amudalat Ajasa for this story about the significant benefits of CR Boxes for wildfire smoke particles and other indoor aerosol particles (including virus-laden respiratory aerosol particles, pollen, mold, particles from cooking, etc.).

www.washingtonpost.com/climate-solu...

#8 Repair public trust:

If the risk of an epidemic escalates, the public should be presented a clear picture of what is happening and what the plan to counter it is in advance of a full-fledged crisis.