Carbon dioxide (CO2) is an odorless and colorless gas which at elevated levels may cause symptoms such as headache, fatigue, and lethargy. CO2 is commonly associated with combustion and it is also the by-product of respiration. For this reason, IAQ investigators will measure carbon dioxide levels indoors to assess the relationship of human occupancy in an indoor space to the ventilation rate (amount of air delivered to an indoor space via the ventilation system). Generally, outdoor levels measure between 350 and 450 ppm, while indoor levels measure below 1,000 ppm. Measurements above 1,000 ppm may suggest that the ventilation rate of a building should be modified to improve IAQ.
Carbon monoxide (CO) is an odorless, colorless, tasteless, and nonirritating gas. It is produced whenever carbon-based fuels are burned such as gas, oil, kerosene, wood, or charcoal. In addition to carbon monoxide, nitrogen oxides, sulfur dioxide and particulates, are also produced during combustion.
Carbon monoxide may accumulate indoors as a result of tobacco smoking, poorly ventilated appliances, vehicle exhaust entrainment to the HVAC system, and underground garages. An estimated 1,500 people die each year because of carbon monoxide poisoning and thousands of others end up in hospital emergency rooms. At high concentrations, carbon monoxide can cause coma and death within minutes. Carbon monoxide enters the blood from the lungs and combines with hemoglobin, blocking the blood’s ability to carry oxygen to body cells. The two most common causes of fatal or near-fatal CO poisoning are misuse or malfunction of heating devices and motor vehicle exhaust.
Hydrogen sulfide gas is also known as “sewer gas” because it is often produced by the breakdown of waste material. Hydrogen sulfide can affect several different systems in the body. Exposure to lower concentrations can cause eye irritation, a sore throat and cough, shortness of breath and fluid in the lungs. These symptoms usually go away in a few weeks after exposure ends. Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory and dizziness. Breathing very high levels of hydrogen sulfide can cause death within just a few breaths. There could be loss of consciousness after one or more breaths. This high level exposure would not be expected in a home, but could occur in a workplace. Improperly installed or insufficiently maintained plumbing fixtures and pipes are the primary sources of the gas.