Exposure
For an actual exposure to an indoor air pollutant to occur, four components must be present:
- The occupant
- Source of pollutant (where did it come from? - e.g., a mold colony, urea- formaldehyde binder in a pressed wood product, a contaminated humidifier, etc.)
- Pathway (how did it get to where it caused the problem? - a physical route from source to occupant)
- Driving force (a physical energy to drive the pollutant from source through pathway to occupant - such as gravity, air pressure,capillarity, diffusion, etc.)
Without any one of these factors, an indoor air exposure cannot occur.
Many people incorrectly assume that energy conserving or "energy tight" homes are more susceptible to indoor air pollution than homes kept deliberately leaky. These people may be surprised to learn that properly designed and maintained energy efficient homes can have a better quality of indoor air than leaky, drafty homes.
This is because in new, energy efficient homes, and in older homes that have had energy conservation features correctly installed, many pollutants are less likely to enter the homes, and those that do can be removed with controlled ventilation. Remember, in a home that is left intentionally leaky, there is no way to control the air that enters through cracks and other openings. That air flow is affected by wind speed, topography, vegetation, and many other factors. On the other hand, energy efficient homes using properly designed HVAC systems, exhaust fans to remove excessive moisture and cooking odors, and a tight building shell can ensure that potential toxins do not enter the home.