Indoor Air Quality Effects on Health and Comfort
It is important to distinguish between the various contaminants in terms of their health effects. The HVAC designer and building operator may take different approaches to contaminants that can be detrimental to health and those that are merely annoying. Although it is the annoying aspects that will draw immediate attention from the occupants, it is the health affecting contaminants that are of the utmost short and long term importance. It is useful to think of contaminants in terms of the following classes of effect:
Fatal in the short term
Carcinogenic (cancer causing substances)
Health threatening
Annoying, with an impact on productivity and sense of well-being
Fatal in the Short Term
At times, contaminants are found in buildings in concentrations that can cause death. These include airborne chemical substances, such as carbon monoxide, or disease-causing bacteria and other biological contaminants.
Carbon monoxide, a colorless and odorless gas, is produced during incomplete combustion. It is attributed as the cause of many deaths each year. One source of carbon monoxide is a malfunctioning combustion appliance, such as a furnace, water heater or stove. Another possible source of carbon monoxide is the exhaust that results from operating a combustion engine or motor vehicle in an enclosed space.
Certain disease-causing bacteria can be present in the air in the building. These include contagious diseases, such as tuberculosis, exhaled by people who are infected with the disease. The tubercle bacillus is very small and tend to stay afloat in the air. Exposure can be minimized by isolating affected individuals, and by using special ventilation methods.
A third group of contaminants are disease causing bacteria that are generated by physical activity or equipment. One, which is particularly dangerous for people with a weak immune system, is legionella. Legionella is the bacteria that causes Legionnaire’s Disease. Legionella multiplies very rapidly in warm, impure water. If this water is then splashed or sprayed into the air, the legionella bacteria become airborne and can be inhaled into a person’s lungs. Once in the lungs, the bacteria pass through the lung wall and into the body. The resultant flu-like disease is often fatal.
The source of a legionella outbreak can often be traced to a particular location, such as a cooling tower or a domestic hot water system. Where we know the source and the mechanism of transfer of disease to the individual, we call it a “building related illness.”
The pollutants that are fatal in the short-term are often unnoticeable except as a result of their health effects.
Carcinogens
Carcinogens are among the most significant contaminants because of their potential to cause cancer in the long-term. The risk of cancer increases with level and time of exposure to the substance. The exposure may be unnotice- able and not have any immediately apparent impact in the short-term. However, in the long-term, even low levels of exposure may lead to severe, irreversible health problems.
Environmental tobacco smoke (ETS) has been one of the major concerns in maintaining good indoor air quality. Concern has been heightened by increased evidence of its role in lung and heart disease. Most tobacco-related deaths occur among the smokers themselves, but tobacco smoke in the indoor air can also cause cancer in non-smokers. The smoke also causes physical irritation, annoyance and dirt on all exposed surfaces.
Another carcinogen of concern in some places is the gas radon. Radon is a naturally occurring radioactive gas that results from the decay of radium in the soil. This radioactive gas leaks into buildings where it can be inhaled and potentially cause cancer. In places where radon is an issue, it can be controlled by venting the crawlspace, sealing all cracks, or by pressurizing the interior so as to minimize radon entry.
Health Threatening
Many indoor air contaminants (such as allergens, volatile organic compounds, bacteria, viruses, mold spores, ozone and particulates) can be physically irri- tating or health threatening, although they are not usually fatal. Among the most common symptoms is the irritation of delicate tissues such as the eyes, skin, or mucous membranes. Many contaminants cause cold-like symptoms that are often mistaken as the effects of a viral infection.
In some buildings, a significant proportion of the occupants may experience symptoms. If the symptoms disappear when the occupants have left the building, one can surmise that something in the building is causing the symptoms.
If 20% or more of the occupants experience the symptoms only when they are in the building, then they are considered to be suffering from “sick building syndrome.”