@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
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