Ask A Scientist© Environmental Earth Science Archive

name         Teressa R.
status       educator
age          40s

Question -   I checked the Archives and found that question #5 in 
the oxygen category asked Dr. Pam about human oxygen requirements but no 
specific answer was given. Considering the government recommendation that 
a "safe room" be prepared (though airtightness seems an unrealistic 
goal), shouldn't oxygen requirements per capita be known to determine the 
size of the room to be prepared in relation to the size of the family 
living in it? I have a large family and if this precaution is of any 
benefit, I want to choose and prepare knowledgeably. So, what ARE human 
oxygen requirements for elementary aged children to adults?
-----------------
Dear Teressa,  A VERY reasonable question.  The fact that the government
has not provided this information is another indication that it should not
be taken seriously.  However,

I found a web site which stated that an average adult each day consumes 4 lb
of food, 2 lb of water, and 6 lb of oxygen.  I could not find a
corroborating site, but the numbers seem roughly reasonable.  Assuming 6 lb
of oxygen per day is right, how large a room do you have to seal?
Incidentally, an exercising adult uses oxygen at about 15 times this rate,
so remain calm!

6 lb is about 2.73 kg.  Since a mole of oxygen has a mass of 32 gm = 0.032
kg, an adult needs about 85 moles per day.  Since a mole under standard
conditions (atmospheric pressure, 300 C) occupies 22.4 liters, 85 moles
occupies  about 1900 liters or 1.9 m^3.  But air is 21% oxygen, so about 9.1
m^3 of 321 ft^3of air is required for one adult for one day.  If your
ceiling is 8 ft high, this means you need 40 ft^2 of floor area per adult
per day.  So a room 20 ft square (400 ft^2) would provide for 5 (quiet)
adults for two days.  That air would be rather stale, so you would want a 
factor
of at least 2 or 4 to make the air more breathable after two days.

I hope you find this discussion useful and I hope MUCH more that you will
never have the need to use it!

Best, Dick Plano, Professor of Physics emeritus, Rutgers University
=====================================================
Second Note as follows:

I had looked around and had not found the FEMA recommendation of 10 ft^2 to
provide an adult with oxygen for 5 hours.  However, I find it in remarkably
good agreement with my numbers.

Remember, I said 40 ft^2/adult/day which give 8.3 ft^2/adult/5 hours, in
amazingly good agreement with the 10 ft^2 quoted by FEMA.  With my safety
factor of 4, that becomes 33 ft^2/adult/5 hours, which is much more
conservative than FEMA's recommendation.  Incidentally, I think they should
point out that it's the volume of the room, not the area, that matters.

I don't believe the concentration of carbon dioxide matters (unlike carbon
monoxide).  After all soft drinks are filled with carbon dixoxide.  If the
nitrogen in the room were replaced by the carbon dioxide and the oxygen
level remained constant, I don't believe there would be a problem.

However, I am certainly NOT an expert on medical matters and deeply
appreciate enlightenment.

Many years ago I did a study on whether static sparks could cause fires in
oxygen tents.  I was at Columbia and Prof. Leon Lederman gave me the
opportunity because he was afraid of getting in trouble.  I was young and
foolhardy and made a pioneering study which was published in American
Hospitals magazine.  For years thereafter I would occasionally get a letter
from some legal authority describing an incident where a patient had been
burned to death while in an oxygen tent, causing me to regret my
foolhardiness.  However, I believe my results were correct and, in fact, in
each case I eventually got a letter stating that the patient had been
smoking!  Nonetheless I do not wish to be considered or even to become an
authority on this matter.

Best, Dick Plano...
=====================================================