CO and CO2 – What’s the difference?

co co2 difference

CO and CO2 - What's the difference?

CO - carbon monoxide and CO2 - carbon dioxide are often confused. While the names sound similar they are completely different gases with entirely different makeups. While both are colorless, odorless and tasteless gases and have the word "carbon" in their name they are not the same. The biggest difference is that CO2 is a common, naturally occurring gas found everyday from decaying plant and animal life as well as geothermic activity. CO is not common. It is a byproduct of the burning of fossil fuels such as oil, coal, and gas

The media often adds to the confusion because their inability to discern the two gases adds to the issue. Countless stories abound about injuries or fatalities from CO poisoning when a gas fired generator is run inside a dwelling during natural disasters like hurricanes. During the last decades increased focus on greenhouse emissions have led to a heightened awareness of CO2 especially from automobiles. This confusion can often be overwhelming too leading some to dismiss the gases and the issues they cause altogether.  

It is helpful to understand the similarities and differences between CO and CO2:

About Carbon Monoxide

  • CO is almost entirely a man-made gas that is not normally found in the earth's atmosphere. 
  • CO is produced at dangerous levels by oxygen-starved combustion in improperly ventilated fuel-burning appliances such as generators, oil and gas furnaces, gas water heaters, gas ovens, gas or kerosene space heaters, fireplaces, and stoves
  • The highest CO emissions are produced at dangerous levels by internal combustion engines 
  • CO can be a flammable gas in higher concentrations (sometimes referred to as C1D1 or C2D2 environments) and devices to measure carbon monoxide in these concentrations are normally designed to be explosion-proof.

  • CO is the most common type of fatal poisoning in the world

CO Recommended Levels

  • 0.1 ppm is the current average CO level on the planet
  • OSHA limits long-term workplace exposure levels to 50 ppm (parts per million)
  • Symptoms of mild CO poisoning include headaches, dizziness, and violent vomiting at concentrations less than 100ppm
  • Concentrations as low as 700 ppm can be life-threatening

About Carbon Dioxide

  • CO2 is a common gas in the atmosphere and is required for plant life
  • CO2 is a natural byproduct of human and animal respiration, fermentation, chemical reactions, and the decomposition of plant and animal life.
  • The gas is normally measured at approximately 400 ppm (parts per million).
  • CO2 is non-flammable, with no explosive properties
  • CO2 poisoning is rare; however scuba divers have to watch out for it (the bends)
  • Leaking pressurized CO2 tanks in enclosed areas can be dangerous for occupants - both from high levels of CO2 and from lower levels of oxygen (O2 displacement / Asphyxiation)

CO2 Recommended Levels

  • 410ppm is the current average CO2 level on the planet
  • ASHRAE recommends a 1,000 ppm limit for office buildings and classrooms to ensure overall health and performance
  • OSHA limits workplace exposure levels to 5,000 ppm time-weighted average (over 8 hours)
  • Drowsiness can occur at 10,000 ppm (1%) – common in closed cars or auditoriums
  • Symptoms of mild CO2 poisoning include headaches and dizziness at concentrations less than 30,000 ppm (3%)
  • At 40,000 ppm (4%) CO2 can be life-threatening

What are the similarities and differences between CO and CO2?

  • Carbon and oxygen combine to form both gases
  • Both are colorless, tasteless and odorless
  • Both are in the air worldwide (albeit in different concentrations)
  • Both are released during combustion or fire
  • Both are potentially deadly
  • The molecular weight of CO is 28.01, where the molecular weight of CO2 is 44.1. This means that the CO2 gas is much more dense than CO.  
  • CO2 will collect near floor level while CO will collect closer to the ceiling.
  • OSHA lists danger levels for CO beginning at 35 ppm, and for CO2 starting at a 5,000 ppm time-weighted average. Those are vastly different levels.

Understanding PPM - parts per million

Gas concentrations are measured in Parts-per-million (ppm or ppmv).

The range of concentrations is from 0 to 1,000,000. That's why we call it parts-per-MILLION.  Every 10,000 ppm equals 1% concentration. As an example, instead of saying "1% gas by volume," scientists will say "10,000 ppmv" (10,000 / 1,000,000 = 1%) or shorten it to "10,000 ppm."

For example, it is easier to write that the CO2 level in a room has risen from 400 ppm to 859 ppm than to write the CO2 level has risen from 0.04% to 0.0859%. However, both are correct. When measuring in higher volume it might be easier to write 5% vs 50,000 ppm.

Read more about parts-per-million here.

How Monoxide and Dioxide Got their Names

You can thank the ancient Greeks for giving us their names for numerals:

• mono = 1
• di = 2
• tri = 3
• tetra = 4
• penta = 5
• hexa = 6
• hepta = 7
• octa = 8
• ennea = 9
• deca = 10

This is how we get English words like a triangle (3 sides), the US Pentagon (a 5 sided-building), or decathlon (10 contests). So the first half of monoxide means 1 oxygen atom, and the first half of dioxide means 2 oxygen atoms.

For the second half of each word, we have oxide. Oxide is the name for a simple compound of oxygen with another element or group. For example, add oxygen to the element hydrogen and you get hydrogen dioxide (H20), or water. Other oxides you may have heard of are nitrous oxide (NO2 - laughing gas), or zinc oxide (ZnO - the active ingredient in sunscreen).

In conclusion, regardless of what industry you work in, leaks and overexposure to both gases can occur around you each and every day. Recently publicized fatalities involving both CO2 and CO have refocused attention on the need to accurately and effectively detect and monitor for the presence of gases.

Understanding the gases and being able to prevent potential injuries and hazards from occurring is the best preventive first step you can take.

For additional information on CO or CO2 solutions, please contact our technical sales team. We would be more than happy to assist you and help educate you on the difference between the gases, what makes them hazardous and what devices can better assist in eliminating potential injuries from occurring.

Source: Wikipedia


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