If you have a house that is hermetically sealed using ICFs or well applied SIPs, there is very little air exchange with the outside.  I've read that the standard is that if the place is depressurized with a blower door by 10 mmHg, only half the volume of the air in the house should infiltrate in from the outside.

Anyways, what happens if the power fails and you remain inside for a long time?  The joke is that you wouldn't worry about the brownout for long, but does anyone know for certain?  Just how much air exchange do you need to avoid death by asphyxiation?

True, the prudent homeowner would crack a window after the power failed, but what if you were asleep?  Would you even wake in the morning without your ERV circulating fresh air in?

While I won't say that will never happen, I think you are borrowing worry.  Even if you are asleep in an airtight home, there would be plenty of oxygen in an entire house to sustain life for a nights sleep.  Granted if you had a faulty wood burning stove or gas furnace that had a leak, and you lost power 5 minutes after you fell asleep, AND you didn't have a carbon monxide or gas detector, AND there was NO air getting in, then yeah you are gonna die. 

Just cracking a window and using common sense should prevent death.  Your allergies may take a hit but thats about it.  Thats of course in my humble opinion. 

I actually just read an interesting article by FEMA the other day, about 'panic rooms', or safe rooms. It suggested that you can survive in an completely airtight room for five hours per square foot of floor space, per person. (I presume with an 8 foot ceiling, but it never did mention that specifically)

So even if you have two people in a 10X10 bedroom, you should be able to survive for one full day, anyway.

There is 21% oxygen in the air. When you exhale (breath out) there is 16% oxygen left. You will wake up in the morning, if you are sensitive you might have a slight headache.

If you're that sensitive you should never drive to the top of a hill (or even walk too fast), eh? ;-)

Unless you never open the windows or doors (EVER!) you won't run out of oxygen unless you light the place entirely by candles and leave a gas burner on the stove running for hours & hours without an exhaust fan. 

But humidity will likely climb to uncomfortable levels over a few days.  High humidity for weeks/months will lead to high mold spore counts, etc..  Ventilation to some minimum is a good thing, heat-recovery ventilation is a better thing from an overall energy efficiency point of view.  But windows work, eh?  And very few houses are SO tight that serious problems could occur if it takes you a week or two to get the ERV back up & running.

Or you could use one of these to monitor the situation and get an idea of how things are going.

http://www.co2meter.com/collections/desktop-iaq-meters/products/co2-temperature-humidity-meter

I realize that is does not measure oxygen - but it would seem that if there was a lot of breathing/respiration and little ventilation that the oxygen would go down as the Co2 goes up. 

That being said a slight drop in Oxygen should not be a big deal (up to a point) as long as the person in question does not have any cardiopulmonary disease (COPD - angina - asthma et cetera).  People hike all the time up to 10,000 ft elevation where O2 level is lower while exercising and do fine. 

Low O2 in the home could make one feel a little breathless though especially with climbing stairs.  If you are worried you can pick up a "pulse oximiter" online.   Normal pulse ox in healthy adults should be above 92-93% at rest while breathing room air. 

I would of course definitely worry much more if one had natural gas stove/heat/or hot water in the house.  Those levels could go up and this monitor would not register it.  But natural gas smells (not intrinsically but because of the additives) and so should be noticed. 

For my case our ICF house is GSHP - electric water - electric stove.  It would seem sensible that very tight homes have very few if any sources of indoor air pollution.  The PassiveHaus, as I understand, has no heating system other than small electric heater.   Why put yourself in a bubble and then put toxins in the bubble? 

This is all reassuring I guess in regards to oxygen and Co2.  What the VOC level would do I have no real idea.  I see there are some VOC monitors for sale on the web - but I don't use these at work like I do the above monitors so am not as familiar. 

Of course I may buy one and see. Maybe you sit in your tight home and fart and the monitor goes off.

Or a more mathematical approach -

- Inhaled air has 21% O2 - exhaled air has 16% O2.

- Typical adult resting breath (the so called "tial volume") = 500 ml

- Typical respiratory rate is 16 breaths per minute.

- In one minute 8 liters of air (16 breaths/min X 0.5 L) should go from 21% to 16% O2.

- 500 ml of air with 21% O2 has 105 ml of oxygen

- 500 ml of air with 16% O2 has 80 ml of oxygen

- therefore in one breath an adult should extract approx 25 ml of Oxygen.

- in one minute an adult should extract 16 X 25 ml of O2 = 400 ml of O2 = 0.4 liters of pure Oxygen

- 1000 sq ft of house with 9 foot ceilings should have 250,909,920 cm^2 of air volume

- 1 liter = 1000 cm^2

- 1000 sq ft of house should have 250, 910 liters of air (and therefore 21% of that would be 52,691 liters of oxygen)

- Since 0.4 liters of pure oxygen is enough for one adult for one minute - 52,691 liters should be enough for 131,727 minutes

- assuming a person could only extract half of that (i.e. breath the house down to an O2 level of half normal or 10% (still more than Mt. Everest which people have done without O2) then one would only have 65,863 minutes or 45.7 days of air.

So Habeed - if your ERV shuts off and your house is really hermetically sealed and you have 1000 sq foot per person and no cardiopulmonary disease ----->

Start your stop watch - I figure you have about 45 days to live.  

If you have plants or your house leaks at all this would be longer of course.

If any of my math is off please feel free to correct me and I will re-edit. 

An 80 cubic ft scuba tank lasts me an hour (with no recirculation and at some depth). Say 2000 sq ft house = 16,000 cu ft, so far more than 200 hours. 45 days sounds reasonable.

Of course the VOCs may get you within the hour :-).

On the commercial building side, some codes permit Demand Controlled Ventilation rather than a fixed ventialtion rate such as 20cfm/person, etc.

This requires a good control system and CO₂ sensors.  I believe the max permitted CO₂ is 700 PPM.  There is an ASHRAE code number for DCV, but I do not recall what it is.

Bruce