What is CO2 content?

Carbon dioxide is a non-toxic gas. It has beneficial uses and is the "fizz" in carbonated beverages. When frozen, it is "dry ice". At concentrations of from 2,500 ppm to 5,000 ppm carbon dioxide can cause headaches. At extremely high levels of 100,000 ppm (10 percent) people lose consciousness in ten minutes, and at 200,000 ppm (20 percent) CO2 causes partial or complete closure of the glottis.
Carbon Dioxide (CO2) is considered the leading substance for the pollutants that can lead to "sick building syndrome". It is assumed that the occurence of these symptoms can be reduced by 70 to 85% through increased air-conditioning, controlled indoor air quality through the use of CO2 air quality monitors. 


Since carbon dioxide is a product of human or animal respiration (or breathing), it is found almost everywhere. Measurable amounts are seen in lecture halls, homes, classrooms, office buildings, and submarines. Carbon dioxide has been used:

  • In the carbonation of beverages
  • In chemical processing
  • As a food preservative
  • As an inert "blanket" to fight fire
  • For low temperature testing of aviation, missile and electronic components (in liquid form)  

Spreading of CO2

 Carbon dioxide is commonly used as an indicator of the adequacy of ventilation systems. When the windows and doors are closed, all buildings need ventilation both summer and winter. In homes, this ventilation is typically provided by the normally occurring leaks and cracks around windows and doors. New, energy-efficient houses are now so tight that most leaks have been eliminated and some type of ventilation system may be needed. In commercial buildings the required ventilation is typically provided by a fresh air intake to the heating and cooling system.

Unfortunately, many firms have closed the fresh air intake to save energy. Many other systems were installed without fresh air intakes.

Since carbon dioxide is produced by human respiration, the amount of carbon dioxide can be easily used as an indicator of the adequacy of fresh air ventilation in occupied buildings. Outdoor levels are approximately 300 ppm. The ASHRAE standard requires that sufficient fresh air be provided to keep the level below 1,000 ppm. The CO2 levels in buildings with sufficient ventilationwill range between these two readings. Buildings with insufficient ventilation will range from 1,000 ppm up. Often the levels will be low in the morning and increasewhile the building is occupied. In buildingsoccupied during the day the reading should be taken in mid-afternoon, because this is when the CO2 reaches its highest level. 

To determine ventilation rates, the carbon dioxide levels inside and outside the building must be measured in parts per million (ppm). The ventilation rate is equal to the value 10,500 divided by the difference in indoor and outdoor CO2 concentration. The ventilation rate will be in cubic feet per minute (cfm) per person

Health Effects

Symptoms caused by carbon dioxide are directly related to the fact that increasing carbon dioxide levels cause decreasing oxygen levels in the body, hampering the flow of oxygen to the brain. If the concentration of the gas is still relatively low, common symptoms include headaches, an increasing pulse rate, uncharacteristically high fatigue, and breathing difficulties. When concentration of the gas reaches a high level above 30,000 ppm (parts per million), symptoms can include heavy nausea, dizziness, or vomiting. At these levels asphyxiation or a loss of consciousness can also occur, but this is hardly likely to occur in a common home, where levels of carbon dioxide usually range from 300 to 2,000 ppm.

Methods of control

As with most other gases whose problems arise from long-term accumulation, one of the most effective ways to prevent a buildup of carbon dioxide is to use a balanced, mechanical ventilation system, which will reduce indoor CO2 levels and eliminate many other harmful indoor air contaminants. Other preventative measures in keeping the gas at an acceptable level include ensuring that all gas burning appliances are properly vented, and regularly checking on any and all fuel-burning appliances.