C02 monitors are selling like hotcakes, thanks to COVID-19

Originally published at: C02 monitors are selling like hotcakes, thanks to COVID-19 | Boing Boing

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This is kind of old news and was happening last year. And I’m thinking with the massively more infectious Delta variant, the question of whether or not the ventilation is adequate to prevent infection is a pretty solid “no”. Nobody should be taking off their masks indoors. And nobody should be relying on cloth or surgical masks on their own. You need respirator grade masks, or, in a pinch a tight fitting cloth mask over a surgical mask that has good filtration.


The link they are trying to draw between C02 levels and virus propagation is tenuous at best.


Pedant, but surely it’s CO2, not C02?
As in Carbon Dioxide?


If they’re going cheap on the air exchange, it’s only useful as an indication that the rest of their procedures are probably shit too.


What link is that? You buy a CO2 meter as it’s a proxy for aerosol content of the air. CO2 has nothing to do with it, it’s just measurable and indicates the rebreathed air proportion. Our rule of thumb is if it’s heading north of 800 evacuate and ventilate. More than one opening to ventilate.

Obviously air filtration and forced extraction are better medium term solutions.


It’s a rough benchmark for the ratio of fresh air ventilation relative to the number of people inside. Fewer people means less need for venitlation. It’s not meant as an exact analogue of viral propagation.

Those numbers seem like they were useful for the original Covid, but Delta is as infectious as chicken pox it doesn’t seem like ventilation standards have been updated to match this massively increased rate of transmission.


Yeah, I view it as a baseline. I mean, most people are wearing cloth masks, which are more for other’s protection than your own… so unless you’re wearing proper inhalation protection this is all meaningless posturing.

But, if I saw higher values, it doesn’t mean that I take off the mask… but it does probably mean that a surgical mask isn’t going to do much. Fortunately, I’ve got a good n95 with a gel seal so I know it’s relatively safe.

The thing that boggles my mind is the protection of restaurants. I mean, it was a restaurant incident that first demonstrated the aerosolized nature of the pandemic… why are we encouraging people to sit around in a place where they have to take masks off?


Thanks. Very good point.


There was a study* a few months back that there was a concentration threshold. Below it, cloth and surgical masks did provide wearer protection, but above that they overload and the effectiveness drops off quickly.

So when the concentration meter starts rising, oh wait, we don’t have those. So, indoors, wear the best available.

 * the usual cautions, like it probably wasn’t done with Delta.


It’s a good benchmark: it errs on the side of caution. If the carbon dioxide level outside is low enough, and it probably is, then the carbon dioxide the meter measures has probably come from someone else in a public space. COVID does not hang in the air forever like carbon dioxide does. Not all carbon dioxide has come from a person. So, a cheap, mass-produced device can give a figure that in the worst case - all carbon dioxide has come straight from another person - may be proportional to COVID risk.

This is also people thinking about science. Let’s all be really, really quiet, everyone. Don’t tell them off because they haven’t done it your way first go. Maybe they will go on doing it. Maybe the healing has begun…


So basically we are measuring the hot air that gets spewed. No wonder it is higher in GOP strongholds.

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Is it truly a conservative metric?

CO2 diffuses quite rapidly and should be more capable of permeating the structure than an aerosol/droplet. I would imagine microdroplets would behave much closer to PM2.5 particles? Also CO2 will pass right through a HEPA filter so you could have safe air with elevated CO2 in a sealed room…

Determining air changes per hour is not overly complex or expensive (blower tests for example) and should be able to provide some guidance for a structure. I like to think math can do a pretty good job of estimating room capacity based on ACH perhaps moreso than CO2 monitoring?

On a related note (more of a musing, and not directed as a reply to you):
Given the cost of these CO2 meters it wouldn’t be much more expensive to aquire some fans (turbulence helps settle particles out of the air) and large room hepa filters to actually improve safety…


I don’t know. I wouldn’t use it for some standard of COVID purity without some testing, but it seems sensible. It may be cheaper to get a fan than an CO2 monitor, but if I run a restaurant, and you come in and tell me your meter says I need to turn the fans up. The fans and their electricity, and the meter aren’t coming off the same budget.

We might have raised CO2 levels if people have lots of fizzy drinks. There are all sorts of things that may harmlessly raise the CO2 level. I can’t think of anything that is likely to absorb exhaled CO2 so we underestimate the covid risk, but I could be missing something.

I could have used one of those CO2 monitors back in university. The 2nd half of some long lectures felt like murder, and maybe it was…


You need outside ventilation or a HEPA filtration system. Fans on their own will just spread covid aerosols more evenly in the enclosed space and insure that more people are infected.

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Since I mentioned fans first with a very oversimplified comment I’ll expand a little on where I was going.

Particles and gasses behave differently so while some methods will reduce both, others will be more targeted. So it is very possible to have little CO2 and lots of particles…

A simple way of thinking about it is that removal of particles from air requires either moving them from the room (air changes) or removing them from the air (settling on a surface or adsorbtion onto filter media). Particles tend to like to float around in a small area in stale air, but moving air can force them to enter your air filter or leave the room (for example an exhaust fan).

Anyone ever notice you’re supposed to put your free standing HEPA filter in the middle of the room? This is so it actually has the opportunity to not just clean a pocket of air in the corner… Similarly HVAC systems will place the air vents and returns to encourage flow through the room. So proper use of ventilation fans can encourage particles to settle and move to the air filter. I am of course oversimplifying a bit.

Anyone who really wants to dig into details might also enjoy this presentation from the CDC.

Okay, we seem to have go off on the wrong foot here. I am not trying to sell carbon dioxide meters, not do I think they are a reliable indication of covid risk, but they seem to be a neat way of measuring the worst case risk using a cheap, repurposed instrument.

Suppose you are back in my restaurant for some reason: maybe you are a health inspector, and you have to for your job. There are some fans in the wall of the restaurant blowing in air coming in from ducting, but you cannot see where the duct goes. Suppose your carbon dioxide meter is reading significantly higher than it did outside…

The most likely possibility is that the fans are not drawing in air from outside. Maybe the air conditioning outlet and the inlet are too close to each other. Maybe the incoming air is not missing with the restaurant air. I used to work in clean rooms ages ago, and it isn’t always obvious what the air does.

It could be that the air is being filtered and recirculated. This may mean the air is having any covid aerosols removed, and the carbon dioxide level does not correspond to the covid risk. This is the sort of thing they do in passenger aircraft because it is cheaper to filter and recirculate the air than to pressurise and warm the air from outside. This is unlikely to be economic for any public space. Again, it may not work depending on how the air mixes: there are worries that people spread infections on aircraft.

Public spaces might have a set limit to the carbon dioxide concentration over and above the ambient level outside. This may be a cheap and practical measure that may correlate with how healthy the air is. If you feel ill, you take your temperature. Your body temperature is not a measure of how many infectious bacteria you have in you at that moment, or how infectious you are. You may have just come out of a hot bath or sat in from of a roaring fire. But it is a handy measurement if we keep our common sense about us.

I would add the usual cop-out: I would like to see more research on this topic.

Reminds me of a story (Wired? mid-90’s?) of a chip fab’s clean room(s) went out of tolerance, and finding the cause was very difficult and time-consuming. The article mentioned that clean rooms can be finicky and require some “magic touches” to work correctly.

For fun, I made something like this with a $10 Raspberry Pi Zero, a $11 NDIR sensor from China, a $20 ePaper display, and a few dollars of plastic once I get around to printing a case. I imagine something professional would need some more refinement, but there’s a huge gap between $45 and $179. It’s too bad these kinds of things aren’t cheap and ubiquitous. We mainly use our sensors a reminder to open windows.