Last time [see Aug. 31, 2023 blog post] we reviewed the Top Five Best Practices to Minimize Covid-19 Spread. The first three all deal with fresh air ventilation, where we advocate having a fresh air level that complies with CDC, WHO, State of Vermont, and our own recommendations. The approximate carbon dioxide (CO2) level that corresponds with these recommendations is less than 800 parts per million (ppm). The amount of fresh air goes down as CO2 readings go up. The CO2 level in unpolluted outside air is about 400 ppm.
Note that these are all RECOMMENDATIONS, not mandatory or legal requirements. Fresh air ventilation in buildings is only loosely regulated, by design standards for a new or renovated building, and never “enforced” after construction that I have heard of. The only mandatory standard is from OSHA, which is 5000 ppm CO2 over an eight-hour period. (At this level, there is almost no fresh air ventilation and I would hope people would be complaining of the bad smell of the air long before this reading is reached.)
Having excellent fresh air, with CO2 less than 800 ppm, which is “in the green” on our Safetulator meters, reduces the spread of covid-19 and other respiratory illness by a factor of five [see Jun. 10, 2022 blog post], allows our brains to function at a normal high level [see Oct. 14, 2023 blog post], and also dilutes all other smells and air pollutants that might be coming from inside the building, including airborne PCBs.
Last time, we included a handy checklist for taking CO2 readings and being sure HVAC equipment is doing its job. We got some questions on exactly how to implement these practices. Here are the points raised, and the answers.
• How exactly do we do the CO2 tests?
===> To test, enter the room (with typical occupancy), go to a representative spot (not where any air is blowing on the sensor, and not within two feet of a person), wait two minutes for the reading to stabilize, then read the meter.
• How frequently and over what period of time should we collect the CO2 tests?
===> First take baseline tests with the windows closed, and all HVAC systems running normally. If it’s all good, then you don't need to test again unless something changes. You could test once or twice more this school year if you want to be sure something hasn't broken and not been noticed.
• What are the courses of action that need to be taken if elevated CO2 levels are found in classrooms?
===> Step 1: Simply open windows. This will almost always be an adequate solution from a CO2 standpoint, but as the weather gets cold, opening windows will not be acceptable unless the covid-19 virus spread returns to crisis levels. But opening windows buys you time to take care of the more permanent measures, shown below. You can experiment to determine how much window opening is needed—for rooms with all the windows in one wall, often it is just two windows that need to be fully opened.
===> Step 2: Involve your staff or contracted HVAC technicians and check each HVAC unit that provides fresh air to be sure it is passing the fresh air on into the rooms. From the checklist, you already know that the intake openings through the walls or roof are working and that the unit's filters are clean. Now check the inside of the units—follow the path of the fresh air flow and make sure there are no obstructions, or closed dampers. Dampers or their motors may be stuck or failed or may have slipped. There may be an adjustment or setting for the amount of fresh air being delivered, and this setting can usually be increased.
===> Step 3. If there are just a few rooms that are not getting enough fresh air, and if it is acceptable for the doors to these rooms to be open to an adjoining space with better fresh air, these open doors may do the trick. If needed, you can try a small fan blowing in or out through each doorway.
===> Step 4: An excellent way to add "ventilation" is with in-room air purifiers--see our Jan. 11, 2022 blog post. Contrary to that post, the manufacturer ended up NOT discontinuing our favorite model, the Classic 205, and there is also the Classic 280i which is slightly fancier but at the same or lower price. Please consult a mechanical engineer to find out the number of air purifiers needed. Note that air purifiers alone are never enough, as you still need some real fresh air, just not as much of it.
===> Step 5: For long-term HVAC revisions or equipment replacements, consult a mechanical engineer. A complete design guide to this work can be found on our web site at COVID-19 Mechanical Engineering Recommendations (PDF) .
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