Indoor Air Pollution: A Misunderstood Subject

Indoor air quality has a significant impact on both ‘health’ and ‘learning.’

The source of all indoor air quality regulation is The American Society of Heating, Refrigeration, and Air-Conditioning Engineers, or ASHRAE. This organization is the leading professional society in the world dealing with controlling indoor air and setting the standards that buildings operate under. They also make recommendations, which are not standards, and are not binding on local officials.

ASHRAE defines  ‘healthy’ as the inability of 4 out of 5 people in a room to detect the body odor of another person in the room.  A standard was established to ensure this, and is often incorporated into laws and building codes. That standard is 5,000 parts per million (ppm) of CO2.…/TC-04.03-FAQ-35.pdf

But this has nothing to do with ‘learning,’ or how the brain functions at different levels of oxygen or other ingredients in the air.

CO2 is created in a building when people inhale oxygen rich air, use up the oxygen, and exhale CO2.   So crowded spaces or spaces with poor systems to bring in more oxygen rich air from outside can have high and rising levels of CO2 – which makes the brain work less well.

In the following graph, look at how our brains work in 9 different categories of mental functioning (look below the columns for the kind of mental activity being measured), under 3 different levels of ‘healthy’ air.  Notice the dramatic difference in brain function between the white circles at 600 ppm of CO2 and the black circles at 2,500 ppm of CO2.

As the graph clearly shows, 5,000 PPM of CO2 is much too high a level for effective ‘learning’ to occur.


ASHRAE actually recommends that CO2 levels be held to 1,000 ppm. Unfortunately, it is not a legally binding standard – it is only a recommendation – and most buildings were not built to meet it.  See page 35 here:

Why do building designers and builders measure CO2 at all?

One indicator can signal a wide range of  problems

Think of the  CO2 reading as being similar to the “check engine” or “service needed” light on your car’s dashboard.  If the light starts flashing, you know to take the car to a service station.  That blinking light could be triggered by  a broken water pump, a leak in the cooling system, a failing gas tank,  or many other things.  In the case of schools, one measured CO2 because if you detect high levels, you know it is time to call in the experts.

The primary way ASHRAE engineers keep a building ‘healthy’ is to throw away used air, and bring in fresh air.  They do this by using fans to import around 15 cubic feet of fresh air for every room occupant per minute.  If too little replacement air is pumped in, CO2 rises, and the experts are called in – to keep a ‘healthy’ building, but not a building optimal for learning.

You could be ‘healthy’ and temporarily stupid.

Many years ago, the U.S. Department of Defense studied environments like submarines and airplane cockpits. Armed forces members working in these enclosed spaces were observed making careless mistakes while learning, or while executing tasks they had successfully performed many times before. In such confined spaces CO2 levels rise, and the Defense Department found a direct correlation between these rising levels and the occupants’ ability to do their jobs. Mistakes rose when there was too little oxygen in the air, and conversely when the CO2 level was too high.

So, even if architects design a new school to ASHRAE standards, and the builders build it to ASHRAE standards, and the air conditioning people install air conditioning equipment that meets ASHRAE standards, you can still have a school where it is difficult for children to learn. No matter how hard the teacher works, or how many books the child has at home, or how attentive the parents are, if the CO2 level in a building is above 600 ppm, learning is impaired.  And this is reflected in lower standardized test scores, and poor school reputations.

You can see a bibliography of all this research here

So why would a school system ever have high CO2 levels?   The answer is pretty simple once you connect all the dots.

The primary way ASHRAE engineers keep a building ‘healthy’ is by throwing away used air and bringing in fresh. This is where it gets tricky, since energy is usually one of the largest expense categories for any school system, a very close second only to payroll expenses. The way many buildings cut energy costs is by slowing down the intake of fresh air and leaving a bit more already-conditioned air inside the building. This results in less hot or cold air from the outside that needs to be expensively treated, and energy bills go down, all while staying within ASHRAE guidelines.

But learning is impaired, because the school building continues to operate at the standard of 5,000 ppm, and we’ve seen that any indoor air above 600 ppm CO2 reduces learning.

So, if you want to improve students’ ability to learn, improve the indoor air quality.

To see how you can measure indoor air quality, go to the page containing the list of tools available, found here. We may be able to lend those or similar tools to students so they can investigate their own learning environments.

You will also find a library of techniques that can be used to improve the amount of oxygen in the air of the classroom – some of which are low, or no cost. Some of these the students can implement themselves, and learn a great deal in the process. And for those techniques that require more of a monetary investment, the rate of return often exceeds 20% annually – not including the increase in learning.

This page was prepared by Francis Koster, Ed. D.

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