Thread by @HuffmanLabDU

Another good study simulating effects of masks, HEPA cleaners, ventilation in a small meeting room. By NIOSH team incl. Lindsley, et al.
mdpi.com/1999-4915/13/1…

🔸 Masks reduced aerosol by 50% +
🔸 Additive further exposure reduction w/ any combo of HEPA, ventilation
Summary 🧵

2/ For reference, this is essentially the same NIOSH team that did some other really nice work on masks and air cleaners:
e.g.:
And:

3/ The experimental team here used one aerosol source (0.3 - 3 microns) and three recipients, in various combinations. They used a relatively small room (54 m3) with 2 ACH on low fan speed in order to simulate a realistic meeting-type room.

4/ In all cases, universal masking of 4 "participants" reduced aerosol exposure (see diff. between left/right bars ⬇️). Placement & distance also matters. Face-to-face orientation was worst (obv) when unmasked.
Yellow = source; three others = recipients.

5/ Similar to last perspective, but with speaking source (yellow) facing three participants in audience. Person most directly in-line had greatest exposure, but not much different from others farther away. Masks helped a great deal.

6/ Using mechanical HVAC system on three speeds (resulting in 2, 4, 6 ACH) reduced exposure by "~5% per unit increase in air change per hour (ACH)". Again, masks add to further exposure reduction.
ASHRAE & others have recommended for pandemic to crank the delivery of clean air.

7/ Adding 1 or 2 HEPA air cleaners around the room at several locations (when HVAC at 2 ACH) also reduced exposure, whether participants masked or not. Putting HEPAs in center (black bars) reduced exposure the most.

8/ By modeling the aerosol concentration across the whole room, they showed effect not just for three experimental recipients, but for others as well.
Adding HEPA purifiers, especially centrally in room produced lowest exposure (darker colors).

9/ They also tabulated the noise volume (dB) for the various scenarios. One pushback against adding HEPA is the possible noise. This is one factor when choosing a HEPA unit for your needs.

10/ Their work adds to a strong body of literature showing the additive effects of layered aerosol reduction strategies. All layers help:
🔸Masks, especially when tight & high filtration quality
🔸Ventilation, HVAC or windows
🔸Room filtration, HEPA matched to size & placed well

11/ So if you are thinking about getting a HEPA filter for yourself, or maybe as a donation for a school -- do it! See various practical tips & info here:

12/ And if you're looking to a mask for airborne virus protection -- Any mask better than none, BUT wearing one with the best quality & best fit is key. Upgrade to a #BetterMask like an N95, KF94/KN95 from a reputable source, or an elastomeric respirator.