Scary info about air quality

[richi]

 

[Ed Davies]

Interesting. I already watch Tom Scott's videos quite a lot but have now bookmarked Kurtis Baute's for later.

 

Been meaning to look into CO₂ levels here overnight vs wind speed, to examine my assumption that more wind => more ventilation => lower CO₂ levels but a quick look at the data for so far this month doesn't seem to support that. Sure, the night with the highest CO₂ level wasn't very windy and the windiest night was low CO₂ but there are plenty of other nights which don't follow the pattern.

[Jeremy Harris]

I'm not sure if @DamonHD is still around on here or not (he's not posted in a long while) but he borrowed my portable CO₂/RH/temp data logger a couple of years or so ago and did some experiments in a junior school.  IIRC, these showed a surprisingly high concentration of CO₂ in some classrooms, enough to reach the point where concentration was affected. 

 

I can't recall whether he posted the details here or on Ebuild, but will try and dig them out.

[epsilonGreedy]

1 hour ago, Ed Davies said:

Been meaning to look into CO₂ levels here overnight vs wind speed, to examine my assumption that more wind => more ventilation => lower CO₂ levels but a quick look at the data for so far this month

 

 

Are your readings inside the house or for fresh air outside?

 

I wonder if the numbers improve in the spring when things start turning green?

[Jeremy Harris]

CO₂ concentration outdoors doesn't seem to vary very much at all, from the measurements I've done, it seems to sit pretty close to around 400ppm.  The variation indoors is pretty much all from people/pets breathing and the burning of any fossil fuel.  I've measured levels of up to around 1600 to 1800ppm in our bedroom at the old house in the middle of the night.  Here, the house monitoring system rarely records a concentration above about 600ppm.

[Ed Davies]

54 minutes ago, epsilonGreedy said:

Are your readings inside the house or for fresh air outside?

 

Monitor in my bedroom.

[epsilonGreedy]

24 minutes ago, Ed Davies said:

Monitor in my bedroom.

 

 

If you post any bad jokes on the forum at 2am I will put these down to CO2 poisoning.

 

Think I should buy such a monitor as I face a year living in a static caravan.

[epsilonGreedy]

Has anyone considered a smart MVHR control system that adjusts nightime airflow based on CO2 levels?

[Ed Davies]

2 minutes ago, epsilonGreedy said:

Has anyone considered a smart MVHR control system that adjusts nightime airflow based on CO2 levels?

 

Absolutely, that's what I got the monitor for - to be an input, together with relative humidity measurements, etc, into controlling the MHRV in the house I'm building. Measurements above are for temporary accommodation in leaky old rented house.

[epsilonGreedy]

11 minutes ago, Ed Davies said:

 

Absolutely, that's what I got the monitor for - to be an input, together with relative humidity measurements, etc, into controlling the MHRV in the house I'm building. Measurements above are for temporary accommodation in leaky old rented house.

 

 

I am considering something similar

bool assumeWoodSmokeHangsOverVillage = false
DateTime lastMvhrShutdownEndTime = DateTime.Min

...

if ( dateTime.Now.Hour.IsBetween( 18, 23 ) and
    ( windSpeed < 6mph ) and
    ( outsideTemp < 10c )
Then
    assumeWoodSmokeHangsOverVillage = true

if ( assumeWoodSmokeHangsOverVillage ) and
    ( DateTime.Now - lastMvhrShutdownEndTime).TotalHours > 2 )
Then
    // Consider anti smoke ingest shutdown
    if ( house.Co2 < 1000 )
    Then
        mvhr.Stop()

    

 

[Ed Davies]

Yep, lots of factors to take into account, particularly in an off-grid house. Obviously current and expected CO₂and humidity levels but also things like available power now and expected later, inside and outside temperature, midges, neighbour muck spreading, …

 

I think the main consideration will be humidity as this is buffered more by the inside of the house so there's more choice about when to ventilate for it. E.g., if power is plentiful and temperature differences are small you might choose to ventilate more to drive down the RH to the lower end of the acceptable range (30% or whatever) to dry out the walls with the idea that this will mean less ventilation will be needed later.

 

For CO₂, when levels are high you just need to ventilate but you might decide to put up with somewhat higher CO₂ levels when ventilation is tricky (there's not much power available or it'll result in greater heat loss). No idea how much that would matter in practice; it's the sort of thing to experiment with and tune.

[Hastings]

Vlogging stunts like the youtube video above need to be taken with a pinch of salt. There seem to be quite a few big and possibly misleading generalisations made in it but it did make me want me to learn what is Really going on.

Mainly I wanted to know whether it is elevated CO₂ or the (presumed) lowered O₂ inside the tent and inside those US studied classrooms that impares brain function?

Isn't O₂ level also rather important to brain function too? Why no info on those levels inside and outside the tent?

My personal experience of reacting to needing more oxygen in my lungs is frequently to feel sick and light-headed - it's caused by physical excercise and apparently it's good for you.

 

 

[Ed Davies]

39 minutes ago, Hastings said:

Mainly I wanted to know whether it is elevated CO₂ or the (presumed) lowered O₂ inside the tent and inside those US studied classrooms that impares brain function?

 

As a percentage, the reduction in O₂ is tiny compared with the increase in CO₂. Normally the atmosphere contains about 400 ppm of CO₂ and about 21% O₂ which is 210'000 ppm. If the CO₂ is increased to 2000 ppm (increase of 1600 ppm) then the O₂ will decrease by the same amount, to 208'400 ppm, a decrease of 0.762%.

 

Unless I've got the arithmetic badly wrong you get the same reduction by rising 61 metres. I haven't heard that living higher up tower blocks causes symptoms similar to 2000 ppm CO₂.

[Jeremy Harris]

I've experience of reduced partial pressure of oxygen; had to endure a hyperbaric chamber session every two years for around 20 years.  Up to about 10,000 to 12,000ft (reduction in available oxygen from about 21% to around 12% to 13%) there are no perceptible physiological symptoms for the vast majority of people.  Above about 12,000ft symptoms of hypoxia start to become apparent, but hypoxia is insidious, in that you are often completely unaware that you are becoming hypoxic.  The idea of making aircrew do a chamber run every two years was precisely because the symptoms of hypoxia are so difficult to spot.  By sticking you in a chamber with a doctor, then taking you up to 25,000ft, you get a chance (a slim one, in my experience) of being able to detect your own set of symptoms that might, possibly, allow you to recognise that you are hypoxic.  I should add that at 25,000ft with no oxygen most people only remain conscious for five minutes or so, so it was a slightly extreme way of teaching a vital safety lesson.

 

To highlight just how insidious hypoxia can be, this is a tale of the only time in a few decades of flying that I've ever been hypoxic.  Two of us were flying from West Freugh up to Inverness.  I was in the right hand seat, pilot flying was in the left seat.  I did all the flip card checks, and our taxy checks were interrupted several times by a minor airfield emergency (nothing to do with us, but there was a lot of radio chatter).  We lined up, took off, completed the post-take off checks and set the autopilot to climb on a set heading.  We'd been cleared to FL22 (~22,000ft).  About 3 or 4 minutes into the climb I noticed my ears pop more abruptly than usual and made a remark to my colleague, who confirmed his had as well.  We just assumed that the cockpit pressurisation was being a bit clunky (not that unusual). 

 

We sat back for another few minutes, when I spotted the altimeter coming up to our assigned cruise height and mentioned it to my colleague.  He didn't reply, so I gave him a nudge, and found he was asleep.  He didn't wake up, so I wound the height bug down to level us out, but found that I was really struggling to do something this simple.  Not being able to wake my colleague up didn't bother me at all.  I eventually noticed that my vision was fading to black and white, remembered having experienced this in the chamber and thought to look down between the seats at the cabin altitude gauge.  It was showing 22,000ft, when it should have been around 8,000ft.  There was no way I could fly the aeroplane, but I did manage to wind the height bug right down to a few thousand feet, which caused the autopilot to put the aircraft into a steady descent.  I'm not sure if I remained conscious or not, but remember making a pan call much later, telling Scottish Mil that we were doing an emergency descent, so they could clear any conflicting traffic out of the way.

 

My colleague came to just as I was making the radio call, and was as confused as hell.  We sorted things out, cancelled the sortie to Inverness and headed back to West Freugh.  We both regained full consciousness pretty quickly and spotted the cause of our problem before we landed.  During the interrupted taxy checks we'd both somehow missed the pressurisation dump valve check and cross-check, and left it wide open.  There was no way the cockpit pressurisation could have worked, as with the valve open at the rear of the aircraft pressurisation air would have been blowing out as fast as the engines could pump it in.  In the inevitable stack of paperwork we had to complete after we'd landed on, we both noted that neither of us had thought to don our emergency oxygen masks, despite them being stowed at the side of our seats.  Looking back, we were both seriously compromised by hypoxia, and it was pure luck that we came out of it OK.  My colleague was about 10 years older than me, with over 30 years flying experience in fast jets, yet this didn't help him spot that he was losing consciousness.  It was pure luck that I spotted the loss of colour vision.  If I hadn't been concentrating really hard on the flight director display I might well have never noticed that I was on the verge of passing out.  We could very easily have been yet another "pilotless aircraft flying on until the fuel runs out" accidents.  I think I worked out afterwards that we'd have been over half way to Greenland before we'd have crashed into the sea.  Whether we'd still have been alive when that happened is anyone's guess; I think we probably could have been.

 

 

[Ed Davies]

 ?

[Ed Davies]

Having re-watched the video, when the CO₂ was up to 6370 ppmv (15 times normal) the oxygen was only down to 19.7% from the normal 20.95%. As @JSHarris points out, that would be imperceptible.

[Jeremy Harris]

Yes, it was indeed in XX475!

 

 

The red car is my road-going single seater I built when I was up at West Freugh in the mid-1990s

[Hastings]

If you go to sleep in a sealed room, does the human body naturally react to the CO₂ build up by making you wake up? Or is it the same result as when CO builds up - you die without waking up?

[Jeremy Harris]

I would think you'd wake up if the concentration gets high enough to be dangerous, as CO₂ indirectly regulates respiration rate.  If I remember the little bit I learned from aeromedical training years ago, a build up of CO₂ causes the blood pH to decrease and this then triggers an increased respiration rate and, I think, heart rate, as the body increases its efforts to expel CO₂, to try to increase blood pH back to normal levels.

 

I know from experience in our old house that concentrations of more than 4 times the normal level don't seem to make you wake up, they just tend to make the room seem stuffy the following morning.

[jack]

In a house, CO is the real danger molecule, partly because it doesn't cause a fall in pH (and hence your body doesn't recognise that oxygen is being squeezed out) and more importantly because red blood cells strongly bind CO and tend not to release it. I believe the latter element is why even apparently low relative levels of CO can be a problem if you're exposed to them long enough.

[Ed Davies]

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

http://news.bbc.co.uk/onthisday/hi/dates/stories/august/21/newsid_3380000/3380803.stm

 

From the BBC article: “Most of the victims died in their sleep” but a) that's probably sufficiently second hand to be of questionable reliability and b) though the main problem was CO₂ there was also a lot of hydrogen sulfide and sulfur dioxide causing injuries. Probably it didn't occur to most people to run away from the problem - that doesn't normally work when you feel ill.

 

Still, a room would have to be pretty small and well sealed to get to life-threatening levels overnight. It'd be much more likely you'd wake in the morning with a horrid hangover.

[PeterW]

On 08/02/2019 at 16:40, JSHarris said:

Yes, it was indeed in XX475!

 

 

The red car is my road-going single seater I built when I was up at West Freugh in the mid-1990s

 

@JSHarris is that a Hudson ..??

[jack]

1 hour ago, Ed Davies said:

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

http://news.bbc.co.uk/onthisday/hi/dates/stories/august/21/newsid_3380000/3380803.stm

 

From the BBC article: “Most of the victims died in their sleep” but a) that's probably sufficiently second hand to be of questionable reliability and b) though the main problem was CO₂ there was also a lot of hydrogen sulfide and sulfur dioxide causing injuries. Probably it didn't occur to most people to run away from the problem - that doesn't normally work when you feel ill.

 

Still, a room would have to be pretty small and well sealed to get to life-threatening levels overnight. It'd be much more likely you'd wake in the morning with a horrid hangover.

 

Oddly enough, I was reading about this again just the other day. They apparently degas the lake somehow to avoid this problem arising again. There's at least one similar lake somewhere in Africa.

[Jeremy Harris]

59 minutes ago, PeterW said:

 

@JSHarris is that a Hudson ..??

 

 

Yes, one of only two Hudson Mystics that were ever built.  Hudson had produced the prototype Mystic (a metallic blue one) and then decided not to put the kit into production.  I went down to Norwich and found they had a second set of (pretty rough) body panels and persuaded Roy to fabricate a space frame so I could build another car.  It wasn't really a kit car, as all I got was the space frame chassis and a set of body panels, but it wasn't too hard to make the other bits needed.  Hardest part was getting the gear linkage to work, as I fitted a left hand gear change lever and there wasn't much space to fit things (the prototype had a weird central gear lever between your legs).

[PeterW]

What was the engine in that then as the original Hudson was a 3 wheel Renault 5..!