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Carbon Dioxide

Learn what you need to know about carbon dioxide.

Also known as: Carbonic acid gas; Dry Ice; CO2; Diesel Exhaust Component

What is carbon dioxide?

Carbon dioxide is the fourth most abundant gas in the earth's atmosphere. At room temperature, carbon dioxide (CO2) is a colorless, odorless, non-flammable gas, at other temperatures and pressures, carbon dioxide can be a liquid or a solid. Solid carbon dioxide is called dry ice because it slowly changes from a cold solid directly into a gas.

Where is carbon dioxide found?

Carbon dioxide is a byproduct of normal cell function when it is breathed out of the body. CO2 is also produced when fossil fuels (such as gasoline, natural gas and coal) and wood are burned. Surface soils can sometimes contain high concentrations of this gas, from decaying vegetation or chemical changes in the bedrock.

Carbon dioxide exposure

In its solid form, carbon dioxide is used in fire extinguishers, in laboratories, and in theater and stage productions as dry ice to make fog. The use of dry ice can elevate indoor CO2 if the air is not ventilated.

Where CO2 levels in soils are high, the gas can seep into basements through stone walls or cracks in floors and foundations. CO2 can also build up in buildings that house a lot of people or animals, and is a symptom of problems with fresh air circulation in the building or home. High levels of CO2 can displace oxygen (O2) and nitrogen (N2), potentially causing health problems.

How to avoid exposure

  • Have an HVAC (heating, ventilation, and air conditioning) or weatherization contractor measure CO2 levels within your home. If the levels exceed 1,000 ppm, the furnace should be tuned to increase levels of fresh air coming into the building. If levels are above 2,000 ppm, this can be a serious condition that could warrant HVAC modification.
  • Never use a fire extinguisher or dry ice in a manner by which it was not intended.
  • Never enter a liquid manure pit without protective equipment since CO2, along with ammonia, methane, and hydrogen sulfide generated from decomposing manure can quickly cause loss of consciousness and death.
  • Use care when entering silos since CO2 can build up from the decomposing grain.

What regulations and guidelines are available to protect people from carbon dioxide?

There are no indoor air standards for CO2; however, high indoor air levels of carbon dioxide could be an indicator the HVAC system is not working properly.

The amount of carbon dioxide in a building is usually related to how much fresh air is being brought into that building. In general, the higher the CO2 level in the building, the lower the amount of fresh air exchange. Therefore, examining levels of CO2 in indoor air can reveal if the HVAC systems are operating within guidelines. CO2 levels are usually measured in percent (%) of air or parts per million (ppm). High CO2 levels, generally over 1000 ppm, indicate a potential problem with air circulation and fresh air in a room or building. In general, high CO2 levels indicate the need to examine the HVAC system. High carbon dioxide levels can cause poor air quality and can even extinguish pilot lights on gas-powered appliances.

Health effects

Everyone's reaction is different

A person's reaction to chemicals depends on several things, including individual health, heredity, previous exposure to chemicals including medicines, and personal habits such as smoking or drinking. It’s also important to consider the length of exposure to the chemical, the amount of chemical exposure, and whether the chemical was inhaled, touched, or eaten.

Exposure to CO2 can produce a variety of health effects. These may include headaches, dizziness, restlessness, a tingling or pins or needles feeling, difficulty breathing, sweating, tiredness, increased heart rate, elevated blood pressure, coma, asphyxia, and convulsions.

The levels of CO2 in the air and potential health problems are:

  • 400 ppm: average outdoor air level.
  • 400–1,000 ppm: typical level found in occupied spaces with good air exchange.
  • 1,000–2,000 ppm: level associated with complaints of drowsiness and poor air.
  • 2,000–5,000 ppm: level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
  • 5,000 ppm: this indicates unusual air conditions where high levels of other gases could also be present. Toxicity or oxygen deprivation could occur. This is the permissible exposure limit for daily workplace exposures.
  • 40,000 ppm: this level is immediately harmful due to oxygen deprivation.

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Last revised March 29, 2023