Indoor Air Quality Testing: Oxygen Levels and Oxygen Deprivation Effects

One metric that is commonly overlooked in air quality studies is the oxygen percentage in the indoor environment with respect to normal atmospheric composition and how sensitive the human body is to this level. The oxygen levels on present day 21st Century Earth are nominally 20.9 % IF the relative humidity is 0%. (only found in extremely arid regions or dehumidified rooms such as an attic in summer) At one time in the distant past (the days of the dinosaurs) the oxygen levels on Earth were as high as 35 %.

The water vapor in the air displaces oxygen to some extent, so the more humid the air, the lower the % of oxygen. Here is a chart for reference:

Oxygen Level by Relative Humidity - Indoor Air Quality Factor

Oxygen Level by Relative Humidity

The body (particularly the brain) requires oxygen to function because it is a critical component in the cellular respiration process. (also known as the Krebs or Citric Acid Cycle) There are 42 steps in this cycle, and oxygen comes in at the last stage to combine with the H+ hydrogen proton gradient built up in the mitochondria (the “power plant” which is the main producer of ATP – also known as adenosine triphosphate which is the “energy currency” of biological organisms) of cells. Oxygen combined with hydrogen forms water which is the desired byproduct. Without it, the hydrogen atoms would drive the pH balance to a dangerously acidic level and denature proteins and kill all cellular functions.

Hypoxia - Indoor Air Oxygen Levels Deprivation Effects Toxicity Table

Hypoxia – Oxygen Levels Deprivation Effects Toxicity Table

Notice that the safe range of oxygen is from 19.5 – 23.5 % which is only a 4 point percentage window. This illustrates how narrow the levels are between too much and too little oxygen. Too much oxygen (oxygen toxicity) can slow breathing levels to a rate that does not displace enough carbon dioxide (CO2) – a condition known as carbon dioxide narcosis. This typically only occurs when too much oxygen from a supplemental system such as tanks used in scuba diving or medical breathing equipment that is not adjusted correctly. This is virtually never an indoor air quality issue, but it is mentioned here to illustrate that even chemicals typically considered harmless or helpful can have dangerous effects at high enough levels.

So why would oxygen deprivation be an issue – aren’t oxygen levels homogeneous everywhere?

Not necessarily.

Areas with more forestation and foliage typically have higher levels of oxygen than outlying scrub prairies, but more to the point, deep urban environments often suffer from a shortage of oxygen for several reasons:

  • Lack of oxygen emitting plants and trees
  • High consumption of oxygen by dense populations such as found in heavily urbanized cites like Houston, Austin, the Dallas / Fort Worth region, etc. vehicles and other combustion motors
  • Oxidation / formation of chemicals that bind up oxygen molecules such as sulfur dioxides and nitrogen oxides
  • Displacement of oxygen by other gases and vapors such as water vapor, carbon dioxide, etc.

This is why particularly in downtown environments or near other heavily trafficked / polluted areas it is a good idea to know how much oxygen is being received as the chart above demonstrates that even a drop of 1 % or so (say 20.1% to 19.1%) can induce the subtle but deleterious effects of hypoxia.

To quote the early physician / alchemist Paracelsus: ” Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy.”

2 thoughts on “Indoor Air Quality Testing: Oxygen Levels and Oxygen Deprivation Effects

  1. Jeff Elliott

    Is there a home wall mounted O2 measuring device that exist on the retail market. Something like my home thermostat ? If yes, can someone point me in the right direction. Most inquiries I type into ‘ Google Search’ gives me a personal fingertip O2 sensor that measures Oxygenated Blood Levels. – Not what I am interested in. Thank you for you response.

    Jeff Elliott

    Houston, TX

    1. admin Post author


      >Is there a home wall mounted O2 measuring device that exist on the retail market. Something like my >home thermostat ?

      Good question!

      >Most inquiries I type into ‘ Google Search’ gives me a personal fingertip O2 sensor that measures >Oxygenated Blood Levels. – Not what I am interested in. Thank you for you response.

      Yes, those fingertip monitors are known as pulse oximeters which I personally recommend for a first aid kit IF you are qualified to select and use one. (medically trained)

      What you are asking about in regard to Oxygen (O2) sensors that are mounted on the wall are typically only found at the commercial level – often in the configuration of what is known as a 4 gas analyzer / multi-gas analyzer which measures oxygen, carbon monoxide and generally combustible gases which are measured in LEL %. (Lower Explosive Level)

      Because I only use field instrumentation for measurement and not a permanent / semi-permanent unit, I cannot give an official recommendation for one. Just use the search terms mentioned above and you may find a qualified device recommended by a professional as these are used in many industries.

      As an aside, you will probably have an easier (and less expensive) path in purchasing a meter that measures carbon DIOXIDE (not monoxide) or CO2 meter in order to gauge your ventilation quality. While at this writing I cannot give a direct numerical correlation between the CO2 and O2 balance in an environment, it makes sense that in general if your ventilation is good, the CO2 will be decreased with a somewhat correlated increase in oxygen. (but we are talking about fractions of a percent) Reference the table above showing humidity correlation with oxygen under relatively ideal conditions.

      As a side safety note, it is a good idea to have a reliable, accurate carbon monoxide detector to provide early warning of faulty water heaters, central gas heating, or an idling car in a garage which is near a living area. The monoxide levels in a closed garage will climb to dangerous levels in a very short time with virtually any combustion engine. Propane forklifts which are malfunctioning, improperly tuned, etc. are hazards in warehouse environments.

      -JAG of ScanTech


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