Thread by @lisacng

@MCPS recently gave its 45-day notice to the teachers union @mceanea so they may start talks to re-open schools.

📢 Here's what teachers, parents & students should be demanding before they step foot in a school (A thread/1)

Checks on the HVAC system and #ventilation

1. What kind of system does your school have?
2. Is the ventilation rate meeting minimum requirements in code?
3. What can be upgraded in-time for school re-opening?

(/2)

If outdoor air vents are blocked or equipment is not working, exposure could be 2x compared with working system (/3)

CTL = central system with 70% recirculation
DOAS=dedicated outdoor air
TU = terminal unit system with 70% recirculation
NIE = normalized integrated exposure

Depending on the system, your exposure with no controls (no masks, no system upgrades) might be 20% to 7x greater than a CTL (central) system w/ 70% recirculation & MERV 11 filter

NIE = normalized integrated exposure 6 h day, normalized to CTL system with no controls (/4)

If you have a CTL system with 70% recirculation & MERV 11 filter operating at minimum required #ventilation rates, both a contagious person and receptor wearing #masks, exposure is reduced to 0.5 of no-controls (/5)

Error bars account for deficiencies of controls

#Masks are as good as upgrading to 100% OA, MERV 13 filtration or adding a 300 CADR portable air cleaner (PAC)!!!!!!

📢Combining #masks & these individual controls reduces exposure to 0.3 of no-controls! These results are true for the DOAS and terminal unit systems too! (/6)

If you have window units & no mechanical #ventilation, #masks reduce exposure to 0.5 of no-controls

📢300 CADR portable air cleaner could reduce exposure 0.1 of no-controls #MaskUp

⚠️No-controls exposure 8x greater than other systems (/7)

So what's the bottom line?

☑️ Know your HVAC system & #ventilate right
☑️ Know what controls can be implemented
☑️ #masks for everyone at a minimum
(/8)

☑️ #Filtration (MERV 13) works as well as 100% outdoor air
☑️ #PortableAirCleaners w/ HEPA filtration for classrooms where other controls not available
(/end)

We can do this.

More results: nist.gov/publications/s…

@Poppendieck, Polidoro, @dols, Emmerich, Persily