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Pflanzen im Schlafzimmer – die grüne Bedrohung!

Warning: Danger of life!

Warning: Danger of life!

Some precocious, health-conscious housewives keep lecturing us that we must by no means keep any plants in the bedroom, because they simply “breathe away” our valuable oxygen at night! If you google for the corresponding terms, you get the impression that 90 % of the people are firmly convinced of this claim. Frightening to see how many of them seem to lack even the most simple logics: It is well known that, despite all the warnings, many people do have plants in their bedrooms, and yet they still enjoy good health. Shouldn’t this fact be enough counterevidence?


In the desperate hope to weaken this silly myth a little, I will now make a calculation. It is true that plants do not produce oxygen at night, but only consume it; however, this consumption will at most – if ever – come close to that of a human.[1] Thus we will now have a look at the oxygen consumption of a human.
Imagine a room of 3 x 3 m with 2 m to the ceiling. The volume of this room is 3 x 3 x 2 = 18 m³. This means that there are 18,000 liters of air in this room. Out of these 18,000 liters, about 21 % are oxygen and 0.04 % are carbon dioxide.[2] (The rest consists of other gases which do not interest us.) So there are 3,780 L of oxygen and 7.2 L of carbon dioxide in the room. In a diagram, it looks like this:

Oxygen and CO2 content of the air

Oxygen and CO2 content of the air

Now let’s imagine a man who spends the night in our imaginary room. He sleeps for 8 hours, drawing about 18 breaths per minute with a volume of 500 ml each.[3] He thus breathes through 4,320 L of air; the remaining 13,680 L in the room remain unchanged. The exhaled air contains only 16 % oxygen, but 4 % carbon dioxide. Thus our person exhales a total of 691.2 L oxygen and 172.8 L carbon dioxide. If we add these values back to the 13,680 liters of unchanged air, this results in an oxygen content of 3,564 L (19.8%) and a CO2 content of 178.27 L (0.99%) for the whole room. Therefore, after one person sleeping in a small room for 8 hours, the distribution looks as follows:

Oxygen and CO2 content after one person sleeping in a small room for 8 hours

Oxygen and CO2 content after one person sleeping in a small room for 8 hours

The difference is shocking. No wonder people keep dying from lack of oxygen while sleeping. Especially parents’ bedrooms, youth hostels and other multi-person sleeping accommodations have often been the scene of surprising deaths that could have been avoided if only we would raise the public awareness of the immense nocturnal oxygen consumption. (Irony off.)

But seriously: A few small plants in the bedroom will in no case draw more oxygen from the air than we do ourselves in our sleep (and even then there would still be 18.6 % oxygen remaining in our example room). A life partner who is sleeping in bed next to us is a far greater threat to our nightly breathing air than a plant. So if anything, you should throw him/her out first. :P

There is yet another argument that I find quite funny: If the oxygen requirement of plants at night was indeed as high as is always claimed, you would suffocate immediately when taking a night walk in the forest. :P And now have fun greening your bedroom!



Comments

  1. 7th November 2011
    3:52 pm

    Ginchen flag

    Wow, that was elaborate! Thanks for your thoughts on this matter! :D

    You’re right, the feeling of suffocation comes from too much CO2 rather than too little O2. However, what I tried to prove wrong was the myth that plants steal our O2, so that’s why I didn’t really focus on CO2 so much. :)

  2. 1st November 2011
    9:07 pm

    Rob flag

    I found this page because I’ve just moved from one tiny bedroom, where I’d hooked up a fan to blow air in under the door, to another tiny bedroom where I haven’t. Much like I did before I hooked up the fan I now find I’m feeling spaced out the next day… and I’m wondering if dropped O2 or increased CO2 could be the reason.

    Trusting your figures, you’ve shown a 1.2 % absolute drop in O2 levels which on the face of it is pretty small. But then I also found this study http://www.sciencedirect.com/science/article/pii/S0034568798000681 on high altitude adaptation which showed that a 24 % absolute O2 level (using your baseline that would be a 3 % increase over ambient) had all sorts of measurable effects on the study subjects.

    In addition, while your CO2 level goes from 0.04 % to 0.99 % absolute, a tiny change, that’s a 25-fold relative change. IIRC, it’s the level of CO2 in the blood that causes feelings of suffocation, not an absence of O2 – which is why you can pass out if you hold your breath after hyperventilating : the hyperventilation flushes all the CO2 from your system, and you subsequently run out of O2 before CO2 levels rise high enough to prompt you to take another breath. This suggests to me that relatively high levels of CO2 might have more impact on physiology than their tiny absolute levels would imply. I don’t have any data to back this up however : it’s just a hunch :)

    I’m aware that air turnover hasn’t been taken into account here, and usually runs, IIRC, about 1 air change every 3–4 hours even in a tightly sealed room. Still… that’s half the night.

    Anyway, so while none of this makes me in any way doubt that your conclusion about plants is correct, it does make me think I’ll be setting up that fan to blow in under my door again sometime pretty soon [yeah I could leave the door open, but it’s doing a job keeping out noise]. Thanks for doing the calculations :)

  3. 7th September 2011
    9:46 pm

    Ginchen flag

    Du hast recht, darüber habe ich gar nicht so sehr nachgedacht. Der Post entstand ja wie gesagt, weil ich mich darüber aufgeregt habe, dass alle immer denken, die Pflanzen würden den ganzen Sauerstoff aufbrauchen. An CO2 habe ich dabei nicht gedacht.

    Aber trotzdem: Wenn eine Person eine Nacht in meinem imaginären Raum verbringt, sind am Morgen 0,99 % CO2 in der Raumluft. Heißt das jetzt etwa, daß diese Person sich damit schon selbst schadet, weil der Wert ja über die unbedenklichen 0,3 % steigt? ;) Muß ich jetzt nachts immer das Fenster öffnen, selbst wenn ich allein und ohne Pflanzen schlafe? :D

  4. 7th September 2011
    3:52 pm

    Sven flag

    Hey die Rechnung hinkt ein bisschen, da für die Beurteilung der Atemluft auch der CO2 Gehalt beachtet werden muss. Wobei bis 0,3 % CO2 Gehalt keine Bedenken bestehen. Bei 1 % merkst du erste Beeinträchtigungen und 8 % sind binnen 30–60 min tödlich. Soll nicht allgemein gegen Schlafzimmerpflanzen sein aber in dem Raum aus deinem Beispiel würde ich mir keine reinstellen bzw. dann halt immer Nachts das Fenster kippen. Grüße Sven

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