Normal Levels

• Outdoor carbon dioxide concentrations range from 250 to 350 parts per million (ppm) while indoor levels can reach 1,000 ppm without any negative side effects. Heating, ventilation and air conditioning (HVAC) specialists can measure the carbon dioxide levels in homes and buildings to determine if the ventilation systems are working properly. HVAC professionals can adjust the amount of fresh air brought into a home or building by changing the amount of fresh air mixing with the heated or cooled air to keep the levels in line with health standards.
  
  

Higher Concentrations

• When too many people are in a room or a building's heating and cooling system is not working properly, the carbon dioxide concentrations build. When they reach over 1,000 ppm, people experience drowsiness. As the levels build, side effects include headaches, poor concentration and increased heart rates as the heart tries to circulate more oxygen to the cells. The air begins to feel stuffy and stale. At levels over 5,000 ppm, people can go into a coma, experience brain damage and even die.
  
  

Outdoor Hazards

• Decaying vegetation can create dangerous levels of carbon dioxide. Decaying manure in closed containers, compost piles and silos containing decomposing corn or grains may have high levels of carbon dioxide. One of the reasons people turn their compost piles is to introduce more oxygen into the pile to hasten decomposition. The state of Wisconsin recommends wearing protective equipment when entering manure pits or silos to avoid the harmful effects of the high concentration of carbon dioxide gases, as well as methane, which also builds when vegetation decays.
  
  

Prevention

• Paying attention to symptoms when congregated in closed rooms or buildings is the best way to alert someone in charge of maintenance or safety about the possibility of high carbon dioxide concentrations. Building managers can also install carbon dioxide detectors that alert maintenance when the levels reach an unhealthy status. A triggered detector turns on the ventilation system, diluting the concentration to acceptable levels. Wine makers also use carbon dioxide detectors to monitor carbon dioxide levels in the air, since the process of wine-making increases carbon dioxide.