In the ’70s the energy crisis forced people to think about energy conservation. One of the solutions was to build homes that are much better sealed and insulated. In office buildings, there was an increasing trend to minimize the introduction of fresh air to reduce energy costs. Renovations of old buildings to make them more energy efficient did not take adequate ventilation with fresh air into consideration. These changes increased the number of contaminants that accumulated indoors and reduced the amount of fresh air available to maintain adequate indoor air quality. In addition, the use of auxiliary, cheaper methods for heating homes such as burning wood or kerosene also produced more contaminants. If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Add climate or weather conditions with high humidity and those levels can go even higher.
Outdoor air enters a building by: infiltration, natural ventilation and mechanical ventilation. Infiltration is when outdoor air flows into the house through joints and cracks. Natural ventilation occurs when air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between the indoors and outdoors, and by wind. Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchens, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is called the air exchange rate. When the air exchange rate is low, pollutant levels can increase.
Unless they are built with special mechanical means of ventilation, homes designed and constructed to minimize the amount of outdoor air that can “leak” into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, such as high humidity, pollutants can build up even in homes normally considered “leaky.”
Adverse health effects associated with indoor air pollution due to poor ventilation and poorly maintained HVAC systems range from minor discomfort causing decreased worker productivity, to respiratory illness, cancer, and in the most extreme cases, death. Perhaps the most tragic and well publicized example of this was the 1976 outbreak of Legionnaires’ disease at an American Legion (hence the name) convention in a Philadelphia hotel. 221 people contracted the disease from breathing air contaminated by bacteria originating from the building’s air conditioning system. 34 of those people died as a result.
The Department of Health and Human Services Center for Disease Control and Prevention (CDC) estimates upwards of 18,000 people in the United States contract Legionnaires’ Disease every year (OSHA estimates upwards of 50,000 cases per year). Approximately 5-30% who contract the disease will die from it
The Legionnaire bacteria (Legionella pneumophila) is only harmful when inhaled resulting in severe pneumonia (lung infection). The disease is not transmitted from person to person or contracted from drinking water. Legionnaire bacteria multiplies in warm stagnant water where there is also the presence of algae and other organic matter, and is only harmful when inhaled causing severe pneumonia (lung infection). Thus it’s link with water cooled air circulation systems. Legionnaire bacteria also causes Pontiac Fever which has mild, influenza-like symptoms but is not life threatening. Humidifier Fever (similar to Pontiac Fever) and Hypersensitivity Pneumonitis (exposure to molds) can also be caused by poorly cleaned and maintained HVAC systems.
Legionnaires’ Disease highlights the need to keep air conditioners cleaned and maintained on a regular basis. Commercial and residential HVAC systems can provide ideal conditions for the Legionnaire organism and others to multiply. The West Australian Health Department advises these HVAC systems be cleaned regularly. The WAHD also notes that window air conditioning units are the only air cooling devices for buildings that do not contract the Legionnaires’ bacteria.