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Adventures of a CO2 Guerrilla in the Pilates Lion's Den, Part 1

On the list of scary adventure sports, donning lycra and doing leg raises on a Pilates Reformer machine is not traditionally to be found near the top, but take a look at this CO2 trace from a class recently attended by my wife, Carol (@CallMeSafetyMom):


At this level of CO2, just over 4% of each breath you take consists of rebreathed air, as the natty little stickers we recently designed for our Aranets show:


What that means is that over 4% of each breath you take has recently been breathed out by someone else. And, if they have COVID or any other airborne respiratory illness, then it means you are also breathing in their infectious respiratory aerosols. The higher the CO2 level in an unfiltered space, the more aerosols you may be breathing in, and so the more likely you are to get infected.


In this case, there are six Reformer machines in the room, but only four were occupied. Carol was wearing a fit-tested 3M N95 Aura, as was another participant (also a doctor). The instructor was in a baggy blue surgical mask. The other two weren’t masked. Generally, the room is full and you can probably expect a CO2 of over 3000ppm by the end of the session. Generally, too, no participants wear masks. This room, friends, is nothing less than a COVID HOTBOX. 😱


Our conversation went something like this:


ME: “This is crazy. We can’t go back.”

CAROL: “We have to go back. This is really good for my iliotibial band syndrome and my scoliosis, and you’re too fat and you need to get fitter.”

ME: “We can’t. We’ll get COVID eventually, or something else nasty.”

CAROL: “We must. What’s the point of you Tweeting endlessly about multi-layered protections and calling everyone else idiots if we don’t then do anything constructive about it ourselves?”

ME: “I hate it when you catch me out.”



What could we do, though? I mean, it’s not our Pilates studio, after all.


Well, we already wear high quality, fit tested N95 masks, an excellent layer of protection, but still only one layer. Expose yourself to enough airborne germs for long enough while wearing an N95 and it will eventually fail. More was needed and we spent a long time discussing if it would even be feasible to mitigate the risk sufficiently for us to feel comfortable going back.


The room is windowless and evidently has very inadequate ventilation. Luckily, another doctor participant has already donated a small Xiaomi 3H HEPA air filter to the room and, though that one filter isn’t nearly enough (and it isn’t always switched on), it was a start and showed a willingness to at least contemplate the importance of clean indoor air.


At the time of writing, Carol has been back to another Pilates session, this time taking along the two Xiaomi 3H HEPA filters we have at home and plugging them in, to make three in total. Still not enough, but better. She has also made an appointment with the manager to discuss the ins and outs of making the space as safe as it can possibly be.


Next week, I will update you on how that discussion went and show you exactly what you need to do to calculate the required HEPA filter capacity to make a room safe if you can’t improve the ventilation.

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