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Comment by Mistletoe | Hacker News Reader

I own a CO2 monitor and it is shocking how high it can get in a house with two people just existing. 800 ppm or more. Outside air is 410.

In a car with air on recirculate, it was getting to >1220 ppm, a level that impairs decision making and lowers brain function. I try to drive with air on fresh from now on.

I don’t doubt the air in our conference room with 20 people gets super high in CO2 as the meeting goes on, and that would explain a lot of the horrible decisions and thought processes that happen in there. :) I’m going to bring my meter to the next meeting and see what it gets to. We are a group of scientists so it won’t be awkward or weird. If nothing else it will spark discussion and reflection on the decisions that are made there.

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I picked up a CO2 monitor a while ago myself, and the biggest surprise was having it on in the morning in our bedroom with the doors closed. It was easily over 1000ppm IIRC.

Ever since then I've made sure to set my AC system to run the "house fan" for 15 minutes or so every hour at night just to circulate the air in the house, and while the numbers went down significantly, anecdotally I swear that I wake up easier in the mornings now.

Another surprising place that really high CO2 concentrations show up? The inside of full face motorcycle helmets when at a stop. IIRC they quickly reach as high as 20,000ppm! There is also some speculation that full-face motorcycle helmets that stay closed in an accident are more dangerous in some ways, as the high CO2 concentrations in the helmet can be really dangerous to an unconscious person's brain function.

Exhaled breath is about 3.8% or 38000ppm so (20000) that's really high! I'm not too surprised since the turnover rate through a few small holes with a relatively large volume is bad. Reducing the facial volume would help a lot as each breath would expel more CO2 as a fractional percentage.

It seems that any sort of face covering or even significant exercise could raise your ambient CO2 level well above 1000ppm.

I'm a bit surprised that levels 38-60x below our exhalation % (and it's not lack of O2, because you use up less than 10%/breath) has such a significant effect. The one thing that may drive it is that the efficiency of lung ab/desorption goes roughly as the square of concentration so a 2% change in CO2 concentration might be enough to have an effect on O2 and blood pH.

I found the study I read, and I'll re-link it here, it is eye opening to say the least!

https://www.ncbi.nlm.nih.gov/pubmed/15893291

Really interesting article... all the numbers are completely believable, but seem really high based on the conference room effects at 0.1% They even refer to a person without a helmet in still air as being at 2000ppm, which is comparable to the worst tested "school house" data.

I'd argue that if there is an effect here it isn't the O2 concentration since a 1% change in atmospheric pressure happens at about 275ft. That's a pretty small hill!

A 1000ppm change in 02 partial pressure happens in about 30C temperature change. Really, if this is a real effect it better be actually due to some effect of C02 concentration.

Is there a link for the Elsevier-disabled people?

SciHub has it

Unfortunately Unpaywall (tip: install the browser extension!) doesn't find any: https://unpaywall.org/10.1016/j.apergo.2005.01.018

So unless you're willing to go the illegal route through Sci-Hub, I'm afraid you're out of luck.

> "house fan" for 15 minutes or so every hour at night just to circulate the air in the house,

Depending on your climate, this could significantly raise the humidity in your house. Reason is that moisture from the AC coil are wet after the AC turns off. Typically drips off into the pan until next time AC cycles.

If you run the fan you will then evaporate into the air circulating some of the moisture just removed.

I live in florida, so I'm well accustomed to the humidity! But thanks for the tip, I actually hadn't thought about that.

Part of my home automation system is humidity sensors as well, and while they do spike over 65% sometimes (probably when we have the windows open), they stay around 55% to 60% for the past 30 days. Since I'm only running that fan cycle at night, when the AC tends not to run or not run as much, I'm guessing that helps mitigate the effects of that.

Doesn't that heavily depend on the design of the AC system? I know nothing here, so this is heavily a question.

I ask because I have a heat pump for cooling/heating, but the furnace is the blower. I thought when the fan ran, it pulled from the outdoor intake which is in a very different location from the actual heat pump coils.

Thoughts?

The air handler uses inside air only. The compressor heat pump is outside and either runs its cycle strictly on outside air

that moisture came from inside the house. When it drips, it usually drains outside the home. Perhaps it just pedantic, but it won't raise humidity, but it may lower less.

I live in a desert. If only that would release enough humidity to make a difference.

Helmets? That's interesting; I tend to open the visor a bit when at a stop, it gets really warm in there really fast. I know you shouldn't try to take off a helmet in case of an accident, but is opening the visor at least okay?

> I know you shouldn't try to take off a helmet in case of an accident,

At least here in Germany this advice is considered outdated and people in (mandatory for driving) first aid courses get taught a simple technique to remove a helmet safely (ideally with two people).

Reason being is that with the helmet on it is harder to monitor breathing and impossible / very difficult to do CPR, and the helmet will also interfere with the stable side position.

It’s interesting to see how differently first aid is taught across countries. Eg the last training I did in the US (California), I was surprised by two things that I had not encountered when I was trained in France:

- a big concern around pathogens - always have gloves with you and put them on when administering first aid especially if the person is bleeding; use a mouth dam for mouth to mouth and if you don’t have one don’t do mouth to mouth, just chest compressions, etc

- training first aid responders around what to do when a person needing medical attention tells them not to help because they don’t have health insurance (this point was repeated numerous times by the EMT training us, saying it was routine for them to have to deal with it)

Can you expand on your second point, if you have a moment?

I knew someone (in California) who crashed his bicycle on a curb in front of a number of people. He picked himself up and had a bloody but minor wound on his arm. But overall he was unharmed, just some surface bleeding.

"Of course" multiple people called 911, and an ambulance arrived in short order. He had insurance, but he wasn't interested in getting in an ambulance, he wanted to look after his bike while wrapping up his light wound, and then treating it later.

I'm told the exchange was awkward to say the least.

Interesting. I'm an American, and once sustained a bloody but minor scrape of my knee when playing basketball in China. I went to the campus clinic/dispensary to obtain some bandages, since I couldn't find any that were the right size at the nearby convenience store; there, the staff practically tried to admit me, telling me that I had sustained a very serious injury and that I needed to take it seriously and start a course of antibiotics. After an awkward conversation concerning my refusal to take antibiotics without (what I deemed to be) sufficient cause (being mindful and wary of the resistance risks of an unnecessary course), and their belief that I was being disrespectful of their medical expertise, I left with a bottle of antibiotic pills that I never took. My knee was as good as new in a week or so.

Point being, medical cultures can differ quite a lot, even from locality to locality, and the differences can be seen even in the handling of minor scrapes.

In China it's much more common to take antibiotica for minor reasons.

Also big (area wise) skin wounds can get infected even if they are not bleeding.

Correct me if I'm wrong: I think that a wound that is bleeding is a wound that's, at least in part, being protected from infection by 'internal positive pressure'.

My grandpa taught me that; to let wounds bleed freely for a while, if possible, to reduce the chance of infection.

I wonder how valid that is.

Sounds plausible. At the very least it's a mechanical cleaning. Small pieces of dirt get washed away by the liquid blood.

The most surprising things I was taught when taking classes in Germany (which went beyond the mandatory classes you have to take to get a driver's license) are the following. Well, not really surprising once you think about it...

- Mouth-to-nose is usually better than mouth-to-mouth, at least when there is no obstructions (like bleeding, broken nose, snot, etc).

- If you're doing chest compressions, expect a high probability of breaking a few ribs. Don't stop, as it is highly unlikely the ribs will break "inwards" and puncture a lung, and a broken rib is still better than being dead.

- Remove all clothing from the chest area you're working during CPR. Yes, that includes bras, specifically. The reason being that any clothes will hurt your hands/rip your gloves (if you have some)/shave the skin off your hand especially when you have to do CPR for 15mins. Bras in particular often have wires etc in them that will hurt your hands even worse. As one of the EMTs training us put it: "Don't be shy, no time for false modesty, it may cost a life."

- Don't forget to breath when giving mouth-to-*. Also, don't forget to actually lift your head when you breath. Else you will just breath in the spent air again that you and the person you're helping just exhaled. Given that CPR is very physically taxing, according to the EMTs it is quite common for people giving the CPR to faint themselves if they breath incorrectly.

- It is more important to call for help than to do CPR. Always call first, if you're alone. And stay on the phone until you're being told you can get off the line. Apparently a lot of people either do not call, or call, scream some stuff into the phone, then hang up to administer help, often forgetting to tell crucial details like their location because it is such a high stress situation.

- Defibrillators do not actually restart hearts that stopped beating. They essentially stop the heart in order to reboot it in hopes it will restart with a proper pace/rhythm.

> "Don't be shy, no time for false modesty, it may cost a life."

Or it may cost the rescuer quite a bit when a woman regains consciousness half-naked with a man on top of her.

Yeah, it's no surprise this isn't taught in the US...

It's not usually taught, I think, because if you dony have a knife (which is what professional rescuers will use if they need to do this), removing clothes tends to add delay and also involve moving the subject, both of which are strongly contraindicated in most circumstances where a lay rescuers needs to use CPR in the first place.

The man has a pretty good explanation in that case, iff there was a good reason to administer CPR. So what would it cost the rescuer, exactly? Unless you start undressing every unconscious woman you encounter, even if they seem to have no other problems...

People have been sued for injuries caused while performing CPR, so I could certainly imagine someone being sued for undressing a person (without their consent, obviously) to perform CPR.

You can sue anyone for just about anything. But it doesn't seem like a very winnable case to me. Maybe in some crazy jurisdictions. Many places have 'good Samaritan' laws that protect people who are not medical professionals when they cause injuries during a good faith attempt to safe someone's life. I would assume injuries to someone's modesty are included...

At the end of the day, would you rather let a woman in need of CPR die because you are afraid of maybe getting sued, with an even smaller chance of a conviction?

There's also the court of public opinion to consider, in which actual legal standing is irrelevant. Small comfort if you successfully rebuff a suit but lose your reputation in the process.

Not to mention the hassle and expense of defending yourself.

Of course, I agree. My point was just that it's not like my grandparent's suggestion that there could be consequences for the rescuer is unheard of.

In Germany not performing what we call "lebensrettende Sofortmaßnahmen" (stable side position, clearing airways, CPR) is (at least technically) criminally liable to § 323c StGB. I shall also point out that first responders have some legal protections and insurance.

Do you have a link for that? Every time I look into one of these/similar stories it is a shitty insurance company either heavily encouraging or basically forcing the suit if the person wants to be covered for their injuries at all.

This should not happen. Another rule is that you must not to put yourself on top of the victim or walk crossing over the body of other people. Is disrespectful and can be dangerous also. You have to sidestep it and approach from one of the sides.

Somehow I doubt that a side position would substantially improve the situation for either party if the woman still feels violated.

I understand how social rules about touching other people can differ in different cultures, but a side position looks clearly different to a "riding" position to me in this sense.

People feel often ashamed, can feel humiliated, violated, happy, sad, or anything their want, but they have to understand that CPR means that 1) you life is at risk and 2) some stranger(s) will put their mouth in yours and their hands near your breasts for some time. Period of time that can last for many minutes or even hours. Often longer than the duration of most violations. There is often a legal obligation to do it for some people. To pass and quit the area is not an option.

Sorry but there is no time to find a young sexually acceptable partner for you to happily wake up in her/his arms and upload your booze adventure to instagram, forever-happy style. Deal with it. There is nothing sexually arousing in the experience for the rescuers about your vomit taste or about your body leaking different kinds of fluids over yourself. Not even remotely.

what are you supposed to if the person claims they have no insurance?

If the person is able to tell you that they have no insurance, this by itself means they're able to talk reasonably, this means they are conscious and can breathe and so (absent heavy ongoing bleeding e.g. from a gunshot wound) they aren't dying right now - so urgent emergency healthcare isn't really required.

If they can move on their own, then they can get to the clinic of their choice themselves if and when they choose to; if they can't (which can be caused by anything from a sprained ankle to a fractured hip) then they still may prefer to be delivered to the hospital by family&friends or a taxi instead of paying thousands for an ambulance delivery.

good point about using that as an assessment of the persons state of being. they still could be bleeding however which needs to be stopped unless it's just surface scratches, or have broken bones that need temporary stabilizing.

it seems other than for the first point the question only becomes relevant after any relevant first-aid actions are completed.

i have been in a situation where a guy fell out of his wheelchair. he wasn't injured, he just could not get back into his wheelchair and he was to heavy for any of us to help him without us risking to drop him in the process which might have then actually risked an injury. he looked like the kind of person who might not have had insurance. though he didn't make any statement about that and no-one even considered that to be an issue. we saw no choice but to call 911, which sent an ambulance with people who could help (and they knew him too).

i wonder now how we would have reacted if he had told us that he has no insurance. we might have been looking for alternative help with an outcome that could have been good or bad.

with that in mind i'd think other than for the reasons you mentioned the statement should be ignored.

Yeah ever since I read that, I crack the visor or open it when i'm sitting still.

And for opening the visor in accidents, I'm no expert but I believe it would be safe to do if you can do it without moving their head. IIRC the reason you don't want to take off the helmet is because you could strain their neck doing so. If you could move the visor without moving their head, it probably won't hurt, but at the same time I'm not sure if I'd worry about that in this kind of situation (having seen a motorcycle accident, the amount of co2 that person is breathing is, to me anyway, far down the list behind "call 911" and "make sure they don't get run over again").

I think the findings were more to try and get the helmet manufacturers to design systems which let more air in during an accident or when stopped.

[1] has the study I remember reading about, and it turns out that according to their abstract, opening the visor at a stop has little effect on average! So maybe my behaviour of cracking the visor isn't doing much...

[1] https://www.ncbi.nlm.nih.gov/pubmed/15893291

Moving an unconscious person's head or neck can cause paralysis (if they have a spinal injury). Don't do it without training. In a city it's almost surely best just to wait for the EMTs.

Unless it is terribly cold, I always run a small crack at low speeds. My helmet has a notch that is just a half inch of crack. At high speeds the vents pull air through. It is funny because I never thought about CO2, just that it is too freaking hot.

What's your model?

I used to ride with a just-a-bit opened visor because it was so hot in the city, with all the traffic and all, (and the beard didn't help the air flow) so I ended with eye infection because of the dust ingress. So I just bought one with better vents (and audio). Worth every $ even though I had to patch the audio circuitry a bit.

Maybe you should consider upgrading.

Helmets, hell think face masks people buy at the store to protect themselves from the lawn while cutting it. I tried one, felt like I was suffocating.

full face helmets can at times have the same effect if you bundle up to well during winter but I would be loathe to give it up

Yeah I always open my visor when I'm stopped/riding slowly for longer than I can comfortably hold my breath. Depending on the temperature outside, if I don't open my visor it will fog up real fast.

How does kissing affect CO2 levels? I know I've done some stupid things after kissing.

Anecdata, but since I've started wearing SCUBA gear to meetings, I haven't been kissed once. Maybe it's more about high CO2 levels leading to kissing?

I monitored the CO2 in my bedroom every second for three months and I found results similar to you. If I was sitting right next to the sensor in the evening it would go up to about 1900 ppm. Cracking open the window for an hour or so eventually brought things down to the 500ppm range.

What was interesting is how fast the ppm increases when someone enters the room. I would plot the data and see a blip on the graph when I entered. It was within seconds of entering.

I noticed the same when I am sitting near the sensor. I'm thinking though that it is partially due to me essentially breathing onto the sensor and the sensor dynamics having an averaging function so that I'm not sure what the sensor reports and what I breathe in are the same. Repositioning the sensor so it wasn't in the "line of sight" of my breath changed the readings significantly.

Here's a plot. The peaks are when I was in my apartment. The gap in the middle of February was when I went on vacation.

https://imgur.com/a/HtyhTzo

That is really cool. Thanks for sharing, I love it when people collect data.

Your post has made me consider getting a C02 monitor, will something as simple as this 20 buck Chinese version suffice? https://www.newegg.com/Product/Product.aspx?Item=9SIADJN8NP4... Seems a useful thing to have. Separately it is very stressful being on stage at conferences that are stuffy with no fresh air, hot stage lights and probably very low oxygen. I had a friend who did press ups before going on stage to energize herself as the tech conference chair and raise the energy level of the sleepy audience - she got really out of breath!

I can't see that link (it says the product ID is invalid), but I know that measuring CO2 is actually pretty hard and requires some somewhat expensive stuff, but measuring things like O2 is easy (i believe, i'm going from memory here).

So most cheap CO2 monitors are actually just oxygen monitors that aren't actually measuring the CO2 levels but are measuring the drop in O2 levels and extrapolating from there.

I don't know if that matters for what you might want to use them for, but it's something to be aware of.

I don't have mine any more, I actually borrowed it from a friend and it was a fairly expensive one (like in the $200 range) that he was using for some other stuff.

IIRC the thing to be aware of is that a monitor that actually measures CO2 is going to cost several hundred dollars. The cheap ones don't measure CO2, but some kind of VOC as a proxy. So depending on the source of the CO2, they can be more or less accurate.

Something to research. I'm not an expert, just someone who recently did some shopping for CO2 monitors for my home.

What did you end up buying?

I didn't. Part of my requirements are that I can tie the device into my home automation. After doing a lot of digging and not finding something I wanted, I shelved the idea of adding CO2 sensors to my house for now. Decided instead to just assume CO2 was high, and I'm having a whole-house HRV installed in a few months.

Thanks!

I wonder what the number is for people who wear respirators for dust/fumes. There's the paper masks people are most familiar with and the charcoal canisters for working with chemicals. Since it's sealed off would it be even higher than a motorcycle helmet?

There’s probably all kinds of confounding factors here, but on high pollution days (code purple air quality) when I’m bicycling I need to take my N95 mask off every few minutes for “fresh air.”

> I picked up a CO2 monitor a while ago myself, and the biggest surprise was having it on in the morning in our bedroom with the doors closed. It was easily over 1000ppm IIRC.

Any recommendations on CO2 monitors?

I did quite a lot of research trying to find the best CO2 sensor that would also do humidity/temperature. CaDi by nuwave* is what I settled on. An Irish company. I've been using it for a week now and it is working great! Things that surprised me: the difference it makes if I leave all the internal doors open in the apartment, not just the bedroom door. That even leaving one window open just a crack will help with ventilation. And of course how quickly a room with couple of people in it can go above 3000ppm CO2.

*https://nuwavesensors.com/product/cadi-ci-100/

I always sleep with the window open, because the fresh air feels nice.

In evolutionary terms, you could speculate that the nice feeling of fresh air could be an instinctual response directing the organism to seek higher quality air.

I don't have any domain knowledge on CO2 monitors, but I use this one: https://smile.amazon.com/gp/product/B01FYWU2IS/

It's a greenhouse CO2 monitor, which is the most common kind. I've heard that they're not as accurate as CO2 monitors that are designed for humans, but those tend to be much more expensive.

As a full face helmet proponent and user (since I started riding motorcycles in India), your comment really makes sense.

This is something I used to do almost on instinct,usually at lower speeds (because the helmet had a sort of an intake and a vent that worked well at higher speeds).

"...high CO2 concentrations in the helmet can be really dangerous to an unconscious person's brain function"

Yes but no helmet is even worse for an unconscious person's brain function :)

Oh absolutely! I hope I'm not coming across as advocating for people to not wear helmets!

I just thought it was a very interesting study and that helmet manufacturers could possibly find ways to mitigate it.

800ppm is a fairly typical value for indoor CO2 and not really that shocking.

Fun fact: We've known since ~1850[1] that we should probably stay below 1000ppm for indoors, but we based the measure back then on body odor :) (It still bugs me that oddly cognitive impairment starts at the same point a body-odor measure from the 1800s put CO2 levels, and I keep wondering if we're seeing confirmation bias in action)

In general, where you end up is based on airflow. To get below 800ppm, you'll probably need to increase outside ventilation to >10dm^3/s.

[1] von Pettenkofer, "Ueber den Luftwechsel in Wohngebaeuden"

Fascinating. If you were a fan of evolutionary origin stories, you could easily imagine that the negative association with body odor is an evolved "canary in the coal mine" mechanism. That is, once you start being irritated by your cave-mates BO, it's time to step outside for some fresh air (before you are asphyxiated).

That said, I doubt humanity spent enough time in caves or other restricted airflow environments for such a response to evolve...

Additionally, to support the idea that we evolved to detect and dislike body odor, you'd have to make sure that humans even have this trait. Too many evolutionary just-so stories generate hypotheses from limited cultural observations.

This article about one of the few remaining hunter-gatherer people left, the Hadza, might lead you to question the idea that humans have a "dislike body odor" trait:

> While Hadza have a word for body odor, the men tell me that they prefer their women not to bathe—the longer they go between baths, they say, the more attractive they are. Nduku, my Hadza language teacher, said she sometimes waits months between baths, though she can't understand why her husband wants her that way.

https://www.nationalgeographic.com/magazine/2009/12/hadza/

And this despite the theory that hunter-gatherers are probably even better at smelling than we are: https://www.sciencedaily.com/releases/2018/01/180118142744.h...

A larger issue is Hadza like most hunter gatherers don’t live in caves, which are fairly rare in most parts of the world.

The idea of ‘cave man’ is sampling bias because natural caves preserve ancient artifacts which tend to disappear in the open.

I would be interested to see if increased levels of CO2 alter our perceptions of smells/odors. It may become more unpleasant to encourage us to vacate the poorly ventilated area.

School classrooms (20-30 people, 1-2 hours, closed windows, no ventilation) are probably worse than any conference room.

Apparently there was a fad for building schools with no windows. There's a 70s era middle school in the (U.S.) town where I live; it won a design award for its total lack of fenestration. It was supposed to reduce distraction or something.

My schools were all like that. "Kids aren't paying attention to our standardized-test preparation studies! Perhaps we should make schools more like bleak prisons, and force people to spend the bulk of their formative years there! That will certainly result in a more capable general populace."

My HS in central NJ had neither windows in the classrooms, nor WALLS. It was designed like a giant open office bullpen thing and classes were supposed to congregate in vaguely defined areas. By the time I got there in the early 90s, they had already erected borders everywhere out of movable chalkboards, so you basically got a traditional classroom layout but with noise pollution from all the other classes going on nearby. Great job all around. (Though I suppose from the CO2 standpoint we were probably doing better than most!)

The walls were part of a new teaching fad. I lived in a city that tried it out in one school. Each floor was an open plan for the classrooms. This one elementary school was their trial.

The teachers had a love/hate relationship with this plan.

Sounds like HHS. I was there in the 00s and the borders were these "permanent" accordion wall things

In many countries forcing people to stay in a room with no windows would be illegal, and for good reason.

My school was like that. I always heard it was in response to the 1970's energy crisis - windows are bad insulators.

I ran a CO2 monitor in my classroom and found it exceeded 2000ppm on some occasions. Typically it would be 1200-1600. I discussed this with architects when building a new facility, and the new facility tests at <900ppm fully occupied.

I think the high levels before led to worse behavior and lower academic performance. Both seem generally better now.

Same. I run a CO2 monitor in my classroom too. It gets up to 2000ppm very fast without the fan on.

My senior year, the high school installed blowers in each classroom. We were told it was required by a new California law.

I’m not sure it was an improvement: the blowers were noisy and made the classrooms much less comfortable (colder in winter, warmer in summer; it was an older school and the HVAC systems weren’t great). Teachers constantly talked about how they wanted to destroy the blowers. I seriously doubt grades improved. I wonder how previous students managed before our enlightened times.

Buildings used to be much draughtier, so it wasn't so much an issue.

My landlord at my old place was always adding new insulation. Co2 levels there would get really high with windows shut. My new apartment has much lower ambient co2. Both were built 100 years ago.

I think people also used to leave windows open a bit, even in winter. My (Canadian) grandma always did, and I hear it was the custom in Germany.

Modern buildings are made to be hermetically sealed.

Definitely true. You can measure how leaky a building is by sealing it up, blowing air in the door, and measuring how the pressure changes. If it’s very leaky the pressure doesn’t rise as much.

https://en.wikipedia.org/wiki/Blower_door

We used to assume that you’d get enough fresh air from infiltration through accidental sources. With a better sealed building, that’s not always the case and you may need to deliberately bring in outside air. Heat recovery ventilation systems help to do this more efficiently than the inadvertent leaking method.

https://en.wikipedia.org/wiki/Heat_recovery_ventilation

HRVs also let you control where the fresh air comes in and where the stale air leaves. This means you can do clever things like bringing fresh air into bedrooms and removing air from bathrooms.

Thanks. I really hope hrv systems become standard. My brother has one in his house and it seems to help keep down co2.

Do heat pumps ventilate? I have one in my new apartment and co2 seemed higher when it was off. But I was told they are not hrv systems. Maybe the blowing fan just caused more air circulation.

Home heat pumps generally do not have an outside air connection. They assume that your house is drafty enough already.

At least here in BC, I believe it is code to include a fresh air vent with any central HVAC. Our house has one (built in 1992). Of course, if the house is tightly sealed and you don't have an exhaust fan running, it won't suck in much outside air.

Since the climate is moderate where we live, what's been suggested to me is to just run the recirculate fan often/always, and to use bathroom exhaust fans to control fresh air turnover. (As built our bathroom fans are hooked up to a central humidity sensor, and will turn on when house humidity reaches a set level (as well as being able to turn them on in the bathrooms). I'm actually curious whether something exists, or I could rig something up, to turn them on based on CO2 levels as well.

> I hear it was the custom in Germany.

At least when I went to school it was almost impossible to keep a window open except on the hottest days of summers because inevitably n>1 [almost always] girls would start to complain about draft. (edit: is draft in a room with only one opening to the outside a social construct?)

That being said I always keep the window open in my office. There is no draft.

When I was in elementary school, one of my classmates ended up missing school for a while because of a bad heater and carbon monoxide poisoning. That freaked me out. But everything I read was that this was a relatively new problem because newer houses were less drafty than old houses. It wasn’t clear to me (at the time) whether old houses were draftier when built, although I have to assume they were (otherwise carbon monoxide poisoning would have been just as common when those houses were new).

I even remember wearing sweaters indoors when I was young. I assumed that was an effort to save money during the so-called Energy Crisis (better described as a shortage of cheap oil), but it may have just been the natural reaction to inefficient heaters and the building standards at the time.

Yes, building standards have changed dramatically in the last 50 years. In particular, plastic "house wrap" vapor barriers are standard now, which is a product that had be precedent. There is a tremendous amount of air exchange even through a well-built 'solid' wall with no vapor barrier.

A vapour barrier is different to an air barrier... An airtight membrane is not necessarily vapour tight.

Maybe this is a tradeoff people need to consider when trying to reduce their wasted energy in buildings. Maybe try to do some kind of heat exchange in the air exchange?

I know of at least one case where a family was killed because they were using a laser cutter on wood indoors in a well sealed building and the small levels of CO released were able to build up to lethal levels.

How does air recirculation with increasing co2 compare to having to breath/smell car exhaust, cigarette smoke, etc through vents? I started doing recirculation as my default years ago due to that.

Generally, use recirc only briefly when driving through heavy exhaust, smoke, dust, chemicals, smells. Return to fresh air once you've cleared that.

Some sources suggest recirc for heavy traffic -- I'd prefer a good filtration system.

And for rapidly heating or cooling a car, recirc can help. My preference is to open windows & sunroof (where present) to flush out hot air first, in hot weather. In cold weather, the heater won't kick in until the engine has warmed up, so recirc before that buys you little. And recirc + heat can result in fogged windows, so you may want to turn in the AC as well to rduce humidity. (Many cars now activate AC when defrost is selected.)

I rarely keep recirculated air set for more than a minute or two, most often far less.

Fresh just doesn't work well enough compared to recirculated for me. If the car isn't getting cold enough, recirculation being off is always the culprit.

I've questioned why fresh is even there (seems unlikely co2 would be the reason) - it's always going to be less efficient and you can open a window if you want fresh air.

Anecdotally I feel fine driving for 2 hours straight in recirculated air with closed windows.

Fresh is there at least partly because cars didn't used to have AC. If you are driving in-town or stop-and-go having a fan on your face with fresh air takes a bit of the edge off.

Also in heating mode, there's little reason not to use fresh, as we can heat up cars really easily.

Insufficient cooling capacity is likely an AC issue. Might care to have that serviced.

I will if it becomes more of a problem. Also considering putting some kind of transparent barrier between the front and back.

Most cars should be leaky enough to get fresh air in at the same time. This is why you smell skunks even on recirculate.

Isn't that just... what outside smells like? What do you do about smelling people's breath in the air (??) whenever you exit your car?

A side street would see a few cars per minute. Compare that to a freeway where you are continuously surrounded by multiple cars doing high rpm.

I can imagine there is a non-trivial increase in certain gas concentrations, but smelling people's breath? That just seems ridiculous.

I'm going to guess English is not your first language. Breath is also a verb. Example: "I don't want to breath in all the exhaust fumes".

It sounds like you misunderstood my original comment.

Edit: welp sometimes you learn English as your first language for the second time and today is that day for me

> "Breath is also a verb."

I think the verb you're looking for is breathe. Breath is a noun.

I stand corrected. Thank you

Cars are built to mostly recirculate the cabin air when the recirculate option is turned on. Note that cabins are not fully sealed from the outside. You have multiple vents located throughout the car whose job is to keep the outside elements away and let the cabin "breathe".

Leave it on recirculate unless you are defrosting your windows.

You don't need fresh on all the time, but for long trips I will switch to fresh for at least five minutes each hour. You just want to cycle the air in the cabin for less re-breathed air.

My tests with my meter don't imply that is correct. Almost immediately on recirculate the PPM goes up and stays there.

This is almost certainly correct. An unventilated space as small as a car will increase within 30-60 seconds, based on my testing of small indoor rooms.

Wow I wonder if anyone has done a study on any correlation between cabin CO2 levels and driver safety?

Could you recommend a CO2 monitor? How did you decide to purchase the model that you own?

I got this model several months back and have been really happy with it: https://smile.amazon.com/gp/product/B01FYWU2IS/

I got it to monitor CO2 levels in a house without central air. It's pretty amazing how quickly it rises without the air on or a window open. If the air in a room feels "stuffy", it's probably over 1000 ppm.

Yep, that's the one I have. It's fantastic.

It says the CO2 range is from 0-5000 ppm, but exhaled breath has a much higher concentration (according to another comment). Are you able to accurately measure the inhaled concentration in case the breathing happens in a confined space (e.g. helmet or under a blanket, etc.)

I don't use it for confined spaces, so 5000 ppm is plenty for me. If any building I am in is over 5000 ppm I need to leave immediately!

https://www.burntec.com/images/co220b.jpg

in the unlikely event someone manages to shove that thing inside of their helmet, do they _need_ an accurate measurement? if it hits 5000, it can just be read as "way too much".

I have been considering making a CO2 sensor myself using commercially available CO2 detectors [1] , [2] and an Arduino or similar microcontroller, insructions for which abound on the intertubes [3], [4]. Such a device can be made fairly inexpensively.

However, there is a known issue in calibrating the device, as the IR emitter and light sensor change characteristics over time. The calibration requires immersing the device in nitrogen or pure CO2 and is costly and complex. The workaround is to calibrate the device outdoors where there is an assumed 400 ppm CO2.

[1] https://www.co2meter.com/collections/0-1-co2

[2] https://www.epluse.com/en/products/co2-measurement/co2-senso...

[3] https://www.dfrobot.com/blog-70.html

[4] https://www.youtube.com/watch?v=V1uOHOcVZrE

Awair Glow is a very user friendly/cheap one: https://getawair.com/pages/awair-glow

It has an app (and an API) and monitors CO2, humidity, temp, and VOCs. I like it a lot. For me, it mostly serves as a reminder to open the door for a few minutes before bed and let some fresh air in.

I have an Awair (the regular one, not the glow), it doesn't work with Ubiquiti wifi gear unless you turn on legacy mode for the access points.

Had I known that before I bought it I wouldn't have done so.

I'd love a good looking consumer device like this, especially if it synced with Apple Health and/or Homekit or otherwise allowed data export, but all (Netatomo, Awair, Uhoo, etc) seem to get very poor reviews on Amazon, often claiming they are inaccurate. Has anyone seen a good comparison of whats out there with a suggestion for the best?

Dhh recommends awair highly. Convinced me to get one, he tested a lot.

Hasn't arrived yet so I can't comment directly

https://m.youtube.com/watch?v=MRqh8oLY7Ik

I can also recommend that talk and the Awair unit seems to live up to the praise. I know some might suspect shilling by DHH for this product, but given I owe the last 10 years of my career to him, when he speaks I listen a bit closer than normal.

I've been opening the bedroom window before going to sleep but I wonder if it really matters during a normal sleep cycle.

Thanks for the link. I'm getting one.

I have a foobot.

https://www.amazon.com/Foobot-Quality-Monitor-Homeowners-Ren...

I believe you can hook it up to IFTTT and turn on the AC etc if levels are high. You can get real time stats, historical reporting...If you don't want to keep looking at your mobile device it will light up if the air quality is bad.

It also has a VOC monitor, which is rare. I have a new construction house and the VOC was pretty much deadly.

Note that that one does not measure CO2.

Yep, I made that mistake too. They have estimated CO2.

A many others have said... getawair.com seems to have different monitors for this. DHH swears by them. They also just look better imo.

More comprehensive - https://www.amazon.com/Awair-2nd-Invisible-Quality-Chemicals...

Cheaper (smart plug version) - https://www.amazon.com/Awair-Glow-Breathe-Quality-Monitor/dp...

If you're in a heavily trafficked road, particulate matter from other vehicles' exhaust is a far worse threat than elevated co2. Always recirculate on the highway, especially if you sit on it for multiple hours a day for you commute.

Do you have a recommendation for a specific CO2 monitor model that you like?

I have an awair and I’m very happy with it. I have done some highly unscientific testing with it and it seems to definitely register spikes on all sensors when inundated with a given pollutant

"We are a group of scientists so it won’t be awkward or weird"

Story of my life right there

there's a podcast Ashes Ashes (07 - "Last Gasp") that did a whole episode on CO2 and the studies that track the various effects on our health depending on how high the ppm gets. Apparently has a big impact on cognition, and they made the point that all of civilization could be dumber because of base CO2.

You’ll be shocked to find out that’s bunk: https://news.ycombinator.com/item?id=19863319

How many plants are needed to counter this?

Far too many to be plausible. You'd need to live in a terrarium. Which would certainly be nice, but it's a lot of maintenance...

There are plants that do pretty well at air filtering, though not as well as a HEPA filter... but for CO2, they won't absorb more than they can use. This means you need dozens, and also that you'd need grow lights to keep them photosynthesizing as fast as possible.

I've seen an office that was built like that, and it was actually a very nice experience. The owner enjoys spending as hour gardening each evening, though, which is important.

It's far more than you could ever plant, I suspect. I've been in legal marijuana grows in houses where it is nearly wall to wall massive growing plants under many 1000W bulbs and the CO2 still goes up when people go in the house and start breathing and moving around.

When we see science fiction movies and there is a tiny little area with plants that is supposed to be providing the multi-person crew with CO2 scrubbing and O2 generation, I think the size needed is vastly underestimated.

>A human breathes about 9.5 tonnes of air in a year, but oxygen only makes up about 23 percent of that air, by mass, and we only extract a little over a third of the oxygen from each breath. That works out to a total of about 740kg of oxygen per year. Which is, very roughly, seven or eight trees' worth.

from- https://www.sciencefocus.com/planet-earth/how-many-trees-doe...

A typical person exhales just over 1kg of CO2 daily. You'd need emough plants to fix about the same amount of CO2 from the air, under indoor, shaded conditions.

https://www.reference.com/science/much-co2-human-exhale-3f8c...

The fastest rate of carbon fixation by any plants are photosynthetic algae eds, which fix u to 4.4 kg of carbon per square meter per year, or 16.3kg CO2/(m^2 * yr).

http://carbon.ycombinator.com/ocean-phytoplankton/

That works out to about 22 m^2 or 240 ft^2 of algae.

Most land plants offer at best about 1/10th this rate, in full sunlight, and far less in indirect, partial, or shaded light.

A lot.

The source you're citing talks about 4.4 kg estimated per m^2 for algae in the open ocean, and notes that the maximum known rate is 9.16, so around 9 * (44/12) = 33 kg per m^2/yr converting C to CO^2, or around 11 square meters.

In terms of CO^2 sequestration it doesn't seem implausible to fit a farm of that area in something the size of an apartment..

Of course the energy/water use would be insane, hopefully you could funnel sunlight in, or just open the window. But as a thought experiment that ignores the economics of it think more space station than apartment.

Critically, you need on the order of N m^2 of sunlit area on your culture, not N m^2 of floor space. If you image search "phytoplankton culture" you can see that people grow these in bottles or thin plastic bags under artificial lighting, maximizing the surface area.

You can easily fit 11 m^2 in one square meter like that under standard 250 cm ceiling height. Just have a stack every 20 cm.

Note that the article refers to both carbon and carbon dioxide fixation. CO2 weighs more than the carbon it contains, by a lot. Carbon has an atomic weight of 12, CO2 a molecular weight of 44 (12 + 216), or just shy 4x the mass of the carbon* component of CO2.

The 4.4 kg I gave was carbon, the 16.3 kg CO2. Your 9.16 kg refers to CO2, fixed per square meter per year, which is less than the CO2 fixation value I'd used. That is, http://carbon.ycombinator.com are making a more conservative estimate of about 56% the maximum observed rate. That increases rather than decreases the required area.

At 9.63 kg/(m^2yr) you'd need 39.8 m^2, or 429 ft^2, of algae to offset one person's CO2 exhalation.

Using GNU units:

    You have: (1kg/day)/(9.16 kg/(m^2*yr))
    You want: m^2
            * 39.873602
            / 0.025079249
    You have: (1kg/day)/(9.16 kg/(m^2*yr))
    You want: ft^2
            * 429.19589
            / 0.0023299385
    You have: 9.16/16.3
    You want: %
            * 56.196319
            / 0.01779476

Apologies for typos in GP post. Android soft-keyboard stinks.

I understand the difference, but perhaps I misunderstood the article. What it says (and you're correctly referring to) is:
> We will be conservative and say that our algal beds fix 2.5 kg of C per square meter per year and 2.5 kg of C works out to 9.167 kg of CO2.
But then a couple of paragraphs later:
> the maximum CO2 assimilation rate of algal beds which we will say is 9.167 kg of C per square meter per year.
I.e. they first mention a conservative "2.5 kg of C" in the context of the ocean, followed by a "maximum rate". 9 kg of carbon is around 33 kg of CO^2.
Maybe they meant "kg of CO2" in that second paragraph, it's certainly suspicious that it repeats the same 9.167 number, but why would they call that number both "conservative" and "maximum assimilation rate", hrm...

That looks sloppy on their part. Point for my OP was just to note that a couple of potted plants wouldn't keep your apartment breathable.

Wow - imagine the price of that space in an expensive urban center apartment like NYC

This is a chief reason why urban agriculture is at best of limited viability.

Depends on the plant and other aspects of the environment, and actual numbers are hard to find. Also, you need the plants to actively be growing; their steady-state metabolism just temporarily captures carbon and then releases it again.

To get an idea of what you need check out the Biodome and Biodome II projects. They were massive structures chock full of plants to sustain a small handful of people, and it wasn't enough.

Biosphere 2 you mean. Looks like they did two self-sustaining attempts there.
Bio-dome is a movie based on the premise.

Doesn't work. Try exhaling near a co2 monitor and you'll see why. Humans emit a ton of co2, relative to indoor space size.
Ventilation is the only solution.

Also don’t take my word for it, but I remember reading that the viney/dangley kind are better than average for certain pollutants (and they just look really nice dangling from a ledge or window sill)

Some is definitely better than none for more reasons than just air scrubbing, but I believe one of the sibling comments stating “too many to be practical” is probably (and unfortunately) correct

If you want this to work at night, you need a CA (crassulacean acid metabolism) plant.
Practically speaking, that means a bunch of succulents.

I have one too and I can get over 1 000ppm by myself in quite big room while my room also has automatic air recuperation.
I can't imagine how it is in any "van dweller" or "tiny house" place.
If you drive motorcycle, you can get 10 000ppm in your helmet, that is close to being out of mind.

Try owning an EMF meter and not going out of your mind.
The levels of constant radiation we are being subjected to on a daily basis are just off the charts in urban environments.

For in the car, with the air on fresh, does your monitor indicate the amount of CO as well?

No, only CO2.

What kind of car is it? Year/model/mileage if you dont mind.

Thanks for sharing your experience! What monitor do you recommend?

How much would the influence of house plants shift things?

can you link some models? i have a hard time picking one as i don’t know which to trust.

which Air/CO2 monitor is everyone using?

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