Apologies for the long thread. There's been a lot of good discussion about the benefits of portable air cleaners for reducing the threat of short-range aerosols. But I have some concerns about the sound generated in learning spaces that I think still need some thought. 1/

#ksed

The noise produced by these portable units could decrease intelligibility & increase strain on teachers' voices. Looking just at background noise (the sound generated from building services or utilities & from exterior sources such as traffic, lawn maintenance, etc.), 2/

per ANSI S12.60: For core learning spaces 20,000 cubic feet or less, 1-hour steady-state background noise levels should not exceed 35 dBA. For core learning spaces 20,000 cubic feet or more, 1-hour steady-state background noise levels should not exceed 40 dBA. 3/

While probably not as common as under-ventilation, it’s still fairly common to find learning spaces exceeding these levels long enough to have a negative impact on intelligibility, depending on the noise generated from the building’s specific mechanical system as well as... 4/

exterior adjacent activities. While I haven’t exhaustively reviewed the sound output of commercial portable air cleaners what I have seen ranges from approximately 25 dBA - 65 dBA, depending on the size of the fan, level of filtration, thickness of filter, & what speed the... 5/

fan motor is running at. It will likely be greater for DIY units.

Obviously those sitting farther away from the portable air cleaner won’t experience that level of sound, but you can still see that such units running constantly, even at the lowest speed setting, will... 6/

likely raise background sound levels to above what’s recommended for a significant amount of time w/in learning spaces. And noise issues are further exacerbated w/ measures like removing carpets (which absorb sound) also being proposed to eliminate the potential for sending... 7/

settled viruses & other particulate matter back up into the breathing zone.

What does this mean behaviorally? Most of you reading this by now will have experienced what it’s like to have a conversation w/ another person at distances between 3 & 6 feet apart, w/ both of you... 8/

wearing masks. It may also have seemed like it was just harder to make sense of the words you did hear. While most of us aren’t consciously reading lips, not seeing the other person’s lips moving, yet hearing their voice can create a "disconnect" that impacts processing of... 9/

the information being received (made worse when you’re tired or distracted).

Now think about any of these masked conversation episodes you might have experienced w/ some type of noise in the background – HVAC air noise, fans running, somebody mowing their lawn, traffic... 10/

noise, etc. How difficult was it for you to hear & understand the other person? How much did you have to raise your voice? Imagine doing that for several hours throughout the day because that’s what it will be like for teachers & students. And all of the units running... 11/

throughout the building, not just the one or two in the room, will also add to this background sound level.

It will wear on teachers and students in an already stressful pandemic situation where they’re already being asked to do so much out of the norm. As they get... 12/

fatigued, it’s likely masks will drop – in fact I’m almost 100% sure they will. Students may scoot in to hear better, violating the 6’ physical distancing requirements. Portable air cleaners will likely be turned down to the lowest speed (even if it was determined they... 13/

need to be run at higher speeds). Some will be turned off. In addition to risk levels going up, learning will also be negatively impacted.

Just as it’s recommended that mask breaks are needed, it’s likely that “sound” breaks are going to be needed as well in these... 14/

situations. Teachers & faculty should probably have microphones to reduce strain on their voices & increase intelligibility. Teacher & faculty masks need to accommodate this, as well as allow their lips to be seen by students. And maybe in those situations where... 15/

mechanical/natural ventilation & building filtration can’t cut it, learning activities should be moved outside. I'm sure there are other potential solutions, but I think it's something we'll need to account for. 16/