Thread by @DavidElfstrom

One year ago, this was my jump into trying to clear the air around school #ventilation (wherein I miss-tagged Ontario Minister of Education @Sflecce) now at 48 tweets.
Photo is a rooftop classroom exhaust fan turned off because it was too noisy.

https://twitter.com/DavidElfstrom/status/1298001341747548160

That fan is used to force infiltration in through cracks in the building envelope and intentionally open windows. It was a valid design for several decades for ~25% of classrooms in Ontario, ~5% are fully naturally ventilated, and the rest have a HVAC system /2

Some of these have been or are being retrofitted to add ventilation with federal flow-through funding. It's about 🇨🇦$43,000 to add a unit ventilator to a classroom, based on AMDSB @yourschools which is ensuring all its schools have mechanical ventilation! /3

To its credit @ONeducation has done more than other provinces this year, with a last-minute requirement to add a portable HEPA filter into all classrooms without a full mechanical ventilation system ~30% in Ontario. /4

Concerns: (1) Need proper sizing, usually resulting in *several* units to even *begin to approach* #ventilationequity with classrooms that have an existing HVAC system. (2) noise is important. If they are turned to a low speed setting, they aren't doing much cleaning. /5

The last thing I want is for people to have a false sense of security because there's a single HEPA filter in a non-ventilated classroom, quietly humming along at a low flow setting. Then we've gone from hygiene theater to filtration theatre. /6

Good quality masks/respirators are very important for source control. They work together with HEPA. Keep those multiple layers of protection! Figure from cdc.gov/mmwr/volumes/7… /7

A recent thread covering the basics, based on my brief talk at #DeltaSchoolsAirborne: /8

https://twitter.com/DavidElfstrom/status/1428107316998586376?s=20