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Hi All,
Hopefully this is the correct forum for this question, if not Mods please move it.
The question is how long can two (2) average people (a man and a woman) live in a totally hermetically sealed room with a floor space of 90 m2 x 2.7 mtrs high. Total cubic volume 243 m3.
And not succumb to either CO poisoning or asphyxiate by high CO2.
Are we talking weeks, or even a month?
Guestimates are fine.
One person in 56 sq.m x 2.4m = 134.4 m^3 gets 12ish days https://www.physicsforums.com/thread...d-room.685796/
Not accounting for panic causing you to breathe faster, thus exhaling more CO2. Also, CO2 is heavier than air, so it'll be more concentrated at the bottom; assuming these people will sleep on the floor, they might suffocate much earlier than 12 days if there's nothing to circulate the air and keep the CO2 evenly distributed
2 people in roughly double the volume would be similar?
Is there food and water in this room? If not, you'll die in about 3 days anyway from dehydration
EDIT: just saw Bob's post, the link I gave uses 3% CO2 as deadly, taking 10% would roughly triple the time to 36 days or about a month. Seems to check out :rolleyes:
Either way they're still dead from dehydration
Physic Forum guy is using 3% CO2 as the death point - my sources say 7 to 10%.
You can easily stay alive at 3% although it will definitely not be comfortable.
Average resting human breath is ~0.5L with a 4% CO2 content so 0.5 x .04 = .020L of CO2 per breath
Average rate of breathing is 3-4s per breath, lets use 4s so production rate of CO2 is .020/4 = .005 L/s
243 m^3 = 243000 Litres
Death from CO2 start between 7 and 10% CO2 in the air , lets go for 10%
10% of 243000L = 24300 L
To produce 24300 L of CO2 at 0.005 L/s will take 4860000 s = 1350 hours = 56 days = ~2 months
Divide by two people = 1 month.
Different people will have different tolerances so one person is likely to die before the other
Before death severe mental confusion will kick in and it's possible one person will even kill the other one to live a bit longer.
Feel free to check my maths - I literally did the sums on the back of an envelope.
Why do you ask?
[EDIT] Is the room thermally sealed as well?
The human body expires warm air and are warm objects in themselves and will probably provide enough recirculation or air in the room to prevent gas separation.
of heat
The human body generates ~80W of heat x 2 bodies = 160W.
In 2 weeks that's 10^8 joules of heat, enough to take 300 kg of water from zero to 100ªC
Room will be very hot and smelly.
Sim editing - love it.
BTW just finished reading the Martian - love the calculations in that book and I even understood the basic comp sci.
Lol we're editing in tandem
Who you planning on locking up?
Hi All,
It appears as if I have put the cat amongst the pigeons.
For transparency, following is a PM to our benevolent dictator after concerns were raised.
Quote:
Ha Ha Neil.
Yes I fully understand the concern, however it really is quite innocent.
We have recently finished a lengthy court battle with the local council (we were living in a shed whilst we built our house on acreage - which was all legal) where the Building Inspector lied from sun up to sun down etc.
At one point when I rang said council, the receptionist stated that the Building Inspector was concerned for our safety from a CO poisoning perspective, which was clearly ludicrous. It appears that the Building Inspector was trying to justify his position, and sully our reputation. As a side note, I in all probability, have had more to do with CO poisoning and the coroners court/homicide squad than he has. At one stage I was OIC of the Gas & Fuels mobile laboratory checking into issues such as CO/NO/Nox poisoning etc. So I am no slouch in this regard.
My back of the hand calculation, would put the life expectancy in the hermetically sealed room at circa 2 weeks, but I wanted some sort of confirmation to show how inept the Building Inspector was. For the record, we had so many fixed openings, windows, doors, exhaust fans etc that CO/CO2 issues would be the least of anyone's concerns.
Hope this helps Neil. Anything else, please ask. :D
Cheers
George
Even relatively modest CO2 concentrations have a measurable effect on cognitive function. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548274/
sourced from http://dept.harpercollege.edu/chemis...ockfordGas.pdf
Low concentrations (3-5% of CO2) increase the respiration rate and can cause headache.
Levels of 8% to 15% cause headache, nausea, vomiting and may lead to unconsciousness.
Higher concentrations can cause coma and death.
The CDC says the LDLH is 40,000 ppm based on acute inhalation toxicity data. Meaning, I think, you'd sort of drop dead.
In terms of how long you would survive, CO2 being heavier than air will tend to settle near the floor.
should (when?) you became unconscious (asleep) and thus horizontal, you would most probably not re-awake, regardless of how much O2 remained in the upper levels of the enclosed volume.
Given that sleeping platforms are typically less than 900 mm above the floor, the "usable" volume of the initial air is probably only 1/3 of the total.
Accepting BobL's numbers, this would bring the survival time down to less than 20 days, and probably a lot less as the effects of lower concentrations kicked in on metabolism. Boggle & Chandler are thought to have died from CO2 poisoning.
CO - carbon monoxide - is much more serious.
CO preferentially binds to the oxygen receptors on hemoglobin. Because of this 9 ppm is set as the maximum long term exposure, with 35 ppm set as the maximum exposure over an 8 hour day.
at 800 ppm, you would expect to be dead within 2 to 3 hours.
Hmmm, seems some clarification is needed here. Cava, are you talking CO (carbon monoxide) or CO2? You have mentioned both. The former is a product of incomplete combustion & much more deadly than CO2. There have been plenty of deaths due to folks using kerosene heaters & the like in rooms that are far from hermetically sealed. OTH, in cold places like Canada & northern Europe, there are lots of people living happily in houses that are extremely airtight by our standards. No normal person is likely to die of CO2 poisoning from exhaled CO2 in a house. For a start, it's highly unlikely you won't have enough leakage to get a few air-changes per day even in the most assiduously sealed dwelling, and surely someone is going to need to open a door to go out, so subtract that from your calculations on the build-up times you've arrived at, & it gives you a few more weeks of grace.
But if your house is extremely well-sealed, you will likely need some form of ventilation/air exchanger, or the humidity & odours from living/cooking will become both unpleasant & possibly damaging in some areas. It would certainly be inadvisable to use a wood-heater that doesn't have a very well-fitted flue (& preferably supplied with its combustion air directly, rather than using up what's in the room).
Just to add another perspective....
Cheers,
Nope that won't happen.Quote:
Originally Posted by ian
The initial temperature of the CO2 and diffusion will easily keep them well mixed in that size chamber.
Firstly I hope the exhaled CO2 will be warmer than the surrounding air - If not the people will die of heat stress.
Then a human body continually heats the air around it and creates a thermal hot spot which continually adds to the thermal mixing of all teh components in the air.
But the real reason is that gas molecules in a chamber are not stationary instead they have a spread of velocities based on the temperature of the chamber.
All molecules experience this Brownian motion so are constantly bouncing against each other and will diffuse away from any regions of higher concentration to form a well mixed gas.
Now we get really nerdy.
The average KE of molecules in any gas is proportional to the average temperature.
The average KE for the lighter ones will be the same as the KE for the heavier ones which means that heavier gas molecules will on average have lower velocities than the lighter ones.
The fact that they have the same KE means that that the lighter ones are able to kick the heavier ones around equally as well which keeps them well mixed.
There is something else that can partially separate different mass gasses out from each other but that happens on a much larger (km) scale.
At school we used to get the kids to perform a simple experiment by putting a drop of Bromine in a measuring cylinder and sealing it off.
Then we'd put it away and come back the next day to observe the Bromine (a Brown liquid) had evaporated and mixed completely evenly into the rest of the air in the cylinder. Bromine gas (Brown/orange) is Br2 (MW = 160) and the students were then asked to speculate that given its MW is much greater than N2 and O2 why the Br2 doesn't separate towards the bottom of the cylinder. We left at least one of these cylinders on display for a whole year - no separation.
This is quite different when a source of cold/heavy gas, such as from a gas cylinder or Liquid N2, is released near floor level in an enclosed chamber. If the gas is heavier/colder than the surrounding air then it will of course initially pool near the floor but eventually it too will reach thermal equilibrium with the rest of the air and become well mixed.
BTW This has been discussed many times on the internet. It's obviously been set as a homework question by many teachers.
Hmmm, I think it might be easier to just open a window occasionally...... :D
Cheers,
Perhaps the building inspector himself has suffered serious CO2 brain damage and wishes others to avoid his fate....
Hi All,
Thank you for the replies, and it has just confirmed my suspicions that the Building Inspector had lied on this point.
For clarification, the Councils Receptionist was told that the issue was CO (carbon monoxide), which would not stack up in a porous structure such as a building. The CO2 question was just to cover all bases in case I missed something.
Just for the record, our shed living quarters was designed for a passive circa 2.5 air changes/hr.
Thanks all.
CO is only really going to be an issue if you use combustion for heating/cooking.
Are you burning anything inside the living space and of so for how long?
If so, the CO and CO2 from the burning will be a major issue compared to CO2 from breathing.
This is easily fixed by using electricity for cooking.
Cooking would also be a factor, but I did not wish to complicate the question.
That stated, factor in two (2) natural gas burners running at circa 10 mJ/h each twice a day at say 30 minutes each time. Total = 20 mJ/day combined.
The burner(s) are fitted with a flame failure device (similar to an oxygen depletion device). Above the hotplate is a rangehood with a positive pull of 40 pascals. If operated, the ranghood has a claimed non-restrictive flow of 850 m3/hr on maximum. The flue is a straight length of galvanised 150mm x 900mm long venting to atmosphere inside the shed.
Below the hotplate were four (4) 100mm diameter holes to outside air, for combustion/fresh air requirements.